OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines 4hp Briggs and Stratton Quattro

I have a strange question regarding a Briggs and Stratton Quattro engine (the 4hp variety) sorry I don�t have the model type and code on me at the moment.

A guy dropped it around the back of my house and for some reason it got tipped up on its nose and leant against the wall. I was away for a few days and thought it was a little strange when I returned home.

The mower wouldn�t turn so I assume oil had worked its way to where it shouldn�t be. I took off the engine head and oil poured out everywhere. I also removed the valve chest cover to rid the excess oil. I left the mower tipped up with inlet valve open to rid the excess oil.

I fixed the obvious problem being the connector from the coil lead to the plug as it was loose and rusted. I also put on a new boot for good measure. It now has great spark.

So:
Great spark
Carby is clean with new diaphragm
Cleaned the exhaust as best as possible to remove excess carbon (unconventioned tapping with the hammer and then shaking out excess carbon)
Air Filter is clean and oiled
Coil re-gapped
Fixed starter cord as it was about to snap.
Valve clearances are pretty close to specs.
The bore was unmarked
Re-filled with second hand oil to the correct level (new oil goes in when the engine is right to go!)

Now all I can get is the odd pop from the exhaust with black smoke being emitted!

It has a deadmans bar that appears to be operating correctly.

I�ll post some photo�s tonight.

I am obviously missing something and would appreciate some help!

Does it have compression? If so, how much?

Usually, people throw away engines for a reason. It usually isn't a good reason by our standards, but it is nevertheless a reason. Until you have found it and fixed it, you are on borrowed time even if you get it to run. We need to get the model, type and code - I can't help you much without them - but I suggest you focus on two main possibilities.

1. The engine may have valve problems, hence little or no compression - that may be why it was scrapped.

2. The breather pipe will have filled with oil when it was tipped over. The amount of oil still in in the pipe may be enough to foul the spark plug.

I'll get those codes tonight for sure.

Yes the engine has compression - I havent measured it but its more than reasonable from my observations. Its only a couple of years old. I will put the gauge on tonight.

The previous owner assured me it was running but used to stop suddenly. I put that down to a loose connection on the spark plug which I have fixed. I was surpised it even started the HT lead clip was so loose.

Do you have a method to clear the breather pipe? I didnt think of that reason.

Thanks as usual.

If you can use a piece of tube to blow air through the breather pipe, you can clear the tube with a couple of puffs. I suggest you blow it downward into the valve chest if you can.

I'm doubtful that a Briggs engine actually stopped due to a loose plug lead, unless the lead literally fell off the spark plug. There may be a more subtle problem here, but if so, it should make itself known as you move forward.

You may have a sheared keyway throwing the timing out, remove the top nut and starter cup, it should be obviuos if that is the issue or not.

Hi Peter, I have found a couple of similarities with the Quattro 40's over the years, but they may just be a coincidence.
Check you're valve clearances and breather on the valve cover. Try removing the air snorkel (if it has one) and then try starting the engine. The remote filter/snorkel setups for some reason seem to restrict the breathability (if thats a word) of the engine.

Model � 10A902 Type 2164B1 Code 060226511
Excuse the last couple of numbers on the code as my pencil notes from last night smudged a little.
I cleared the breather pipe and a little excess oil came out but nothing notable.
I re-checked the valve clearances and nothing seemed too far out to cause concern.
Inlet - .12mm
Exhaust - .15mm
I checked the keyway and it deffinately isn�t sheared.
I washed the valve chest cover in petrol and made sure it was clear of excess oil. Could a faulty cover cause these symptoms?
It is the model with the foam air filter above the carby, so no snorkel.
After clearing the breather pipe things changed a little. I know get a louder pop and smoke seems to be backfiring around the carby area. Its like a light puff of smoke coming from the whole engine. FYI � the head gasket wasn�t damaged upon removal.
Not something I have encountered before.

First, some basics. The engine was built on 26 February, 2006. I think the last number in the Code is probably spurious and it should read 06022651. The plant which manufactured it is given as 51. Plant 51 seems to be an administrative center (identified as "TBS") at Briggs headquarters at Wauwatosa, Wisconsin, so I suspect you have an early production Chongqing engine. For one reason or another, Briggs does not seem to ever stamp the actual number for Chongqing (Plant 28) on engines made there for export. So far, they all seem to have Wauwatosa admin center numbers.

Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/18hszLXAnfBhU7y.pdf

Here is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/msvtDR-K_ny7tH217FzoPu.pdf

You haven't posted a picture of the engine, but it seems to have a PulsaPrime carburetor as the only option. If yours does not have a primer, please say so.

Now, to the nitty gritty. The cover of the valve chest is also the crankcase breather valve, so it needs to be clean and clear. It has a flat phenolic/fibre flap valve held closed by a spring, which opens momentarily each time the piston moves down the bore. If it is clean, and the valve is not stuck, all should be well.

Because you have a primer carburetor, and those primers are rather prone to not working, one possible cause of not starting, is not having any cold starting enrichment. I suggest you put a small amount of petrol into the cylinder through the spark plug hole, and see if it then starts. If it does, your problem may be an inoperative primer.

I will put some pictures up tonight.

It is a pulsa prime carby.

Any thoughts on the smoke coming from the engine when trying to start. It comes out around the carby and exhaust. Well it appears to anyway. I checked the intake manifold and no cracks were present.

The fuel idea I didnt try as the plug was wet upon inspection. I will try your idea tonight.

Whoa, if the plug is wet and the spark is good, it is way too rich - don't prime it, either with the priming bulb or by putting fuel into the cylinder.

I think you will need to spin it over for a while with the spark plug removed, to evaporate the excess fuel currently in the cylinder. Then try following a normal cold start procedure: say three primes, controls in starting position, and give it a try. If the plug gets wet again, it will sound as if either the air cleaner is blocked, or the carburetor is flooding.

Did exactly as you indicated and no change. I swapped the carby for a known working one and still the same issue. I ended up taking the carby apart and it was full of oil.

For some reason oil was coming out the intake manifold and into the carby causing that puff of smoke I assume.

I am sensing catastrophic engine failure. Any thoughts?

Is that oil coming from the breather tube into the carburetor intake, or is it coming from the intake valve, backwards into the carburetor? Was there oil on the top of the piston when you took the cylinder head off?

You said the carburetor was full of oil. Where was the oil in the carburetor?

Does the engine have normal compression?

I am pretty sure it is coming backwards from the intake valve into the carby.
With the exception of the first time I took the head off there was no oil on top of the piston.

Compression was 100 psi.

The oil in the carby was in the throat of the carby when you look down with the air cleaner off. It also made its way to the diaphragm when I took it off.

I don't see how oil could come from the intake valve back to the carburetor unless there was oil in the combustion chamber, meaning it would be on top of the piston. Also, though less importantly, for substantial amounts of oil to get into the combustion chamber it would have to either come past the piston rings, or through the top of a broken piston. In either case, compression would be low.

Something you might try, is cleaning out the oil from the carburetor and inlet pipe, then disconnecting the breather pipe from the carburetor and spinning the engine several times with the starter. See if oil comes out of the breather pipe, and if oil finishes up in the carburetor. This should tell us for sure, where the oil is coming from.

Ok thanks
I messed up oil is in the combustion chamber because the plug is always oily when I take it out. Sorry about that. I tried your trick after replacing the breather cover with another and no oil was entering the carby either through the throat of the carby or from the breather tube.

So could the breather valve been at fault hence why I tried another

Still won't start though.

Sorry for all the questions

No problem about the questions - that is the whole purpose here.

So, since you changed the breather valve, has the oil stopped entering the combustion chamber?

Once the oil problem is fixed, we should be able to deal with the not starting problem quite easily.

Pete, i dont think you have an oil problem. The fact that the mower was left standing with the plug facing down is the reason for your oil problem. Grab a new plug or hot run that one in another mower to burn off the excess oil. Get some degreaser/carby cleaner and spray through the carby to clean your inlet and through the plug hole to clean the piston/bore. Pull the starter 10-20 times with no spark plug fitted and throttle control in the off position, so you dont get a fire, in order to discharge the excess. Refit plug and start the mower.

The combustion chamber oil problem has no pretty much gone after I used Bigted's idea however still nothing more than the odd pop of two when you try to start the engine. No more oil is entering the throat of the carby.

I should have noted earlier the starter rope sometimes gets difficult to pull like something is providing resistence. The starter itself is fine as i tried it on another mower.

Compression is ok so it should fire more with fuel in the plughole but it didnt. Still thinking........

Have you checked that you are getting a strong, consistent spark?

The symptoms are now a pretty good fit for a sheared flywheel key, resulting in grossly incorrect ignition timing, as rusty ute suggested earlier. Are you sure the key is OK? You need to remove the flywheel nut to be able to see it properly. You may even need to pull the flywheel off to check it definitively.

Yep I have good strong consistent spark. To be thorough I swapped a good known coil onto the mower and still the same result. (Just following the principle you noted about keeping spares of tested parts)

I took off the starter cup and the key appeared ok however I didnt take it off. I dont have a puller (will need to invest in one)

What is the best method to remove the flywheel without a flywheel puller. I have a 2 & 3 arm pullers which I use to remove blade bosses but I dont think my big puller will fit.

Briggs flywheels normally have two untapped holes on the top surface. The holes are the correct tapping diameter for 1/4" UNC screws. They recommend that you just screw two thread-cutting 1/4" UNC screws into the holes. Personally I haven't found those screws for sale in Australia, and I tap the holes with a 1/4" UNC plug tap. You then pull the flywheel easily with a simple home-made flat plate puller and a pair of ordinary hardware store screws:





You only have to tap each flywheel once of course - after that it's easy.

Great detail thanks.
I took the flywheel off last night relatively easily. The key was not sheared and the top crankshaft seal looked to be in good condition.
I took some photos to help but I left my camera at home. I try and load them up tonight.

I'm open to suggestions.

OK, if we have compression and we have strong, correctly timed spark, it's likely we have some kind of carburetion problem. You reported that the spark plug was getting wet, but it isn't entirely clear that it was wet with petrol, given the problem you were having with oil at the time.

I've very occasionally had a problem with a line trimmer that wouldn't fire but had nothing wrong with it. Once I'm completely sure the carburetor is OK (and I'm not really convinced yours is OK), my standard solution is to remove the muffler and apply an electric drill to the flywheel nut. Spin the engine up to 700 rpm for half a minute or so. The only times that hasn't cleared the engine's throat and made it run, has been when I've been missing something obvious, like I've been trying to start it with water in the fuel system or there's a problem in the kill switch circuit that didn't show up in the ignition test. In the case of your carburetor I have no confidence in the primer working properly, but by spinning it fast for half a minute it should start without any choke or priming anyway.

This is not a routine way to start a troublesome Briggs. In this case though I think there is something missing from our communication, rather than a mysterious problem. If my wild guess is correct and the problem is in the carburetor, there's a good chance some fuel will find its way through during the long period of cranking. Removing the muffler for this test is just to cope with the possibility that the muffler is blocked, which we haven't disproved so far.

have you tried a new/known good spark plug?

He's tested the spark Joe, but I agree, a known good spark plug should be tried. This looks like a case where something that has been tested or replaced is nevertheless, defective.

Some pictures of the flywheel removed for reference.

Let's check the governor, in case the spring is not working. To do that, first set the speed control on minimum speed (idle). Look at the position of the throttle butterfly lever: it should be closed nearly to the idle speed screw. Then move the speed control to maximum and see if the throttle butterfly lever has moved to maximum, without you touching it or any other part of the mechanism.

1) The current carby and tank came off a working machine. The primer is spraying fuel into the intake manifold as it should. The primer bulb is retracting as it should and is not staying pushed in. It still won�t fire even when I put a little petrol into the plug hole. It will pop and carry on for half a second but that�s about it. The engine should fire for a second or 2 when petrol is put in.
2) Last night I thought the kill switch might have a fault (the deadmans set-up). So I removed the setup and replaced it with a standard kill switch setup via the throttle control and no change. I guess that took away a possibility.
3) I can confirm the oil problem has been eliminated since changing the breather valve.
4) I have another carby which I could try tonight off another machine I know works.
5) I tried 2 brand new plugs in other machines that worked perfectly. It made no change when put onto this machine.
6) I put a brand new muffler on and it didn�t make any difference.
I don�t have a catcher for this mower (GMC catchers) as they are the flimsy and prone to breaking� so yet another bad point of this mower.
I wasn�t sure about your method of using a drill as I don�t have the attachment to put it onto my battery drill. I have the socket but no suitable attachment. I did however give it 20 good cranks and nothing put the odd pop or two occurred.

Now that the oil is gone and you are confident about the carburetor, let's start again.

1. Test the spark using the actual spark plug you intend to use to run it. We need to know that you are getting a steady stream of blue sparks across the spark plug, whenever you pull the starter.

2. Test the compression the Briggs way: disconnect the spark plug, tilt the mower so the oil runs toward the crankshaft, and rotate the blade plate backwards until you find compression. Then just flip the plate backwards, to see if it will bounce off compression and turn back a bit in the forward direction. If it will, it should have enough compression to run. Reconnect the plug lead.

3. Make the governor check I described in my previous post. This is important.

4. Remove the muffler, and remove the element from the air cleaner but put the lid-retaining screw back in.

5. Set the controls for start (speed control on maximum), verify that the throttle butterfly is wide open, prime the carburetor with the bulb as normal, and pull the starter a few times.

6. Report back.

Essentially, the "odd pop or two" indicates that it is trying to start. Its failure indicates that mixture, compression, or spark is quite a long way wrong. We need to find out which.

1) Definitely has a steady stream of blue spark. I used a plug from a known working engine.
2) I did the blade plate test and the engine definitely didn�t bounce off when compression was found. I suspect lower than anticipated compression in this instance. Is 100PSI on the low end of the scale?
3) I installed a brand new spring on the governor from a known working engine. When the speed control was set to minimum, the throttle butterfly lever was just about closed. When I moved the speed control to maximum the throttle butterfly hardly moved (only ever so slightly)
4) Done
5) Done � throttle butterfly was not wide open though.
6) No change

Bad news � I thought the starter was dodgy giving me the odd clunking type sound so initially I didn�t really worry about it until I got the engine running reasonably well.
Lets just say after watching one of Joe Carroll�s video�s on YouTube, I confirmed the engine has quite a bad knock. Funny thing is that its exactly the same mower as Joe blew up in the video.
Why it will not fire still is beyond me although the lack of compression seems likely. I tried another working 4 stroke and the blade plate bounced back as you indicated.
Worst case this turns out to be a parts mower but I have learnt a few good tricks along the way. If you think its worthwhile looking into further for the experience I�ll await your advice.

Which one did I blow up that time? I think there are 3 or 4 there, the old gmc went off with a pretty good bang sayonara Chinese Briggs.....

yep it was the gmc one! mine makes exactly the same sound. To date I have never found one that bad.

Any suggestions on the not starting would be appreciated! I am sensing compresion given grumpy's advise but I'll wait and see what he thinks unless you have a thought?

I'll be interested in Joe's comments too, Michael. It seems though that your engine has little compression, and a major clunk internally. It sounds like a partly broken (one side of the big-end bearing only) connecting rod, which sometimes happens to Briggs engines that are run without oil, though I think it is more common for both sides of the big-end bearing to break. However from previous threads, especially Joe's posts, about early Chinese Briggs engines, I think the combination of this seeming to be an early production Chongqing engine, and it having a major internal clunk, suggests there is a very good chance that at least one of the connecting rod bolts was not tightened in the factory, and what you have now is a badly damaged connecting rod. If the crankpin is OK, it is possible that replacing the rod would get this engine back into operation.

My guess as to why there is very little compression, is that the loose, mangled big-end results in the piston not travelling far down the bore on the intake stroke, so the compression ratio might only be 3 to one, instead of 6 to one. That is not enough compression pressure for the mixture to ignite.

You might find it interesting to open the crankcase and find out what is actually going on, and whether my guess is correct. Joe is the expert on what you might find in there.

The lightweight blade of a gmc mower gives the false impression that they have compression, I concurr wit hthe thoughts of maybe the conrod bolts never being torqued enough at the factory, and the very obvious fact that they are very pourous castings.

I would say the problem with the compression would be a HUGE ring gap, I have pulled some down before with a (no bullcrap) 5-10mm ring gap, they will act like they are trying to fire up but they are very weak. ill see if I can digup a photo of at least one bad ring gap case I have seen...

this was a 3 year old briggs and stratton with poor compression and just a tad smokey, however I have seen worse.

I agree the not starting, and very little compression, could be just ring gaps Joe, but what about the internal clunks? Peter reported that they sound like your bad Briggs with the loose connecting rod.

Personally I like to do the oil-through-the-plughole trick to check for ring leakage before opening a crankcase.

Grumpy and Joe,
Thanks for the comments - It makes for an interesting thread. I havent had a chance to pull the engine down yet as I've been doing a few other jobs.
I am interested in what you mentioned Grumpy about putting a teaspoon on oil down the plug hole to see if the compression increases. If I read that right, id like to try it.

I will pull the engine down when I get some spare time so I can learn from it.

Funny thing is I got given another GMC which has a 375 Briggs that actually has a snapped rod. It must of went off with a loud bang. What I didnt understand though was the engine had plenty of oil (I am thinking however the owner must have added some oil after it went bang) Nevertheless I'll eventually pull it down to ensure I get all the usable parts off them both.

The oil-in-the-plughole trick is a standard old-time mechanic's test, Peter. It works on the principle that engine oil is fairly viscous, especially when you first put it into the engine (before it warms up, if the engine is warm). It therefore takes a while to be forced past the piston rings by compression pressure, when you pull the starter. This means you can do a compression test, then put in the spoonful of oil and immediately to another compression test. If the pressure increases by more than say 10-15 psi with the oil in there, the rings are leaking. If it is more like 40 psi, which it commonly is with worn out rings, you reach for the spanners.

Just remember not do do something I did a couple of years ago. I was doing the oil trick on an OHV Honda. Those engines have 8:1 compression and therefore take a bit of rotating, especially if you are doing the test with the decompressor disabled, as I was. I therefore used a very large two-handed back-geared electric drill to spin the engine by the flywheel nut. After I got the second reading (the one with oil in the cylinder) my mind must have wandered because I removed the compression gauge from the plughole before I let go the trigger of the electric drill. I was wearing a brand new ODK-logo white T shirt at the time ....

Thanks Grumpy I did some checking on the engine and I am now pretty sure the rings are stuffed.
On a separate note since we were talking about loose rod bolts I thought I�d add a couple of pictures. It is very interesting to note the bolt connecting the rob was loose, supports Joe�s comments.
The engine had plenty of oil when it came into my possession. I was pretty sure it was stuffed and the photos supported my findings.
I have completely rebuilt a number of two strokes however I haven�t split a case on the briggs engines before so I�d appreciate some of your comments around each of the parts and key things to consider about repairing the engine. I have watched a few videos and it doesn�t seem that complicated but I have no doubt there are some special things I should consider like usual.
At worst out of this exercise I have a perfectly straight crankshaft that might come in handy for a future project.
Oh and I haven�t got the piston out of the bore yet.

Funny point - I have never snapped a boss - they must be made of rubbish

While it is commonplace for a side valve Briggs to break its connecting rod, it is nearly always for one of three reasons:
1. Engine run without oil.
2. Engine run with governor disabled, resulting in gross overspeed.
3. Engine incorrectly assembled.

The state of the crankpin is the most likely issue as to whether the crankshaft can be saved. So far as the rest of the engine is concerned, my recollection is that it is an early Chongqing Briggs with a broken connecting rod. There seems little point in regarding it as anything but scrap aluminium. And I don't know what the broken piece is, in that sixth picture.

Thanks Grumpy.
A key point to note was the connecting rod bolt was loose and not snapped. It actually fell out of the rod end which made me immediately think of the engine not being assessbled correctly.
The broken piece in the 6th picture is a piece of the boss and nothing else.
1) The governor was installed properly before I stripped the engine
2) The engine had plenty of oil. Well it could have been filled up after the rod snapped, Who knows some owners don�t care of their machines.
I thought it might not be suitable for repair because of the minimal cost of a replacement block on ebay.
I was hoping you could provide some advice about getting the timing correct if I was in fact going to repair the engine and any other tricks about re-assembling the bottom ends. I�ll no doubt one day be repairing a bigger more worthwhile engine so your advice will come in handy. Ive watched some video�s and they are all slightly different in the way things are explained.

The timing is not much of an issue. The ignition timing will inevitably be correct if the flywheel key is intact and in place correctly. The valve timing requires that you put the camshaft in the correct rotational position when you reinstall it. Briggs engines have timing marks on both timing gears: the one on the crankshaft, and the one on the camshaft. You position the crankshaft so that the dot on its gear is at its nearest point to the camshaft, then you slide the camshaft in so that its dot will end up at its closest possible point to the crankshaft gear's dot. Note that the gears are helical, so the camshaft will rotate a bit as the gear slides into mesh: you have to start with the dot about one tooth below the crankshaft one, because the camshaft will rotate clockwise about one tooth-width as it slides into place. It's a bit like leading a duck slightly when you point a shotgun at it. (Many Hondas don't have a dot on the crankshaft gear, because it is not on a key, it is just pressed on. You use a slightly different method with those - you put the crankshaft on Top Dead Center, then slide the camshaft in so that its dot is as close as possible to the crankshaft gear. I prefer to put a centerpunch dot on the crankshaft gear before I lift out the camshaft, so I don't have the hassle.)

Installing the piston and rod is a bit more complicated, since you have to worry about half a dozen things while you are doing it. This would be a rather long post if I went into all of them.

Grumpy thank�s for your explanation on setting the valve timing. Upon disassembly it was relatively easy to line everything back up as it should be. When find an engine that needs a full re- build and we agree it to be a worthwhile process this post will be good to refer back to as a guide. Your centre punch idea makes the most sense, so I will chalk that up in the memory bank when and if a Honda is on the operating table (my shed bench)
On a separate note I checked the ring gaps of the last 2 dismantled side valve briggs engines and they were both massive. They were not however lined up as Joe thought they might have been.
I have watched a few video�s on correctly installing the piston and rod during a full rebuild and it doesn�t look too complicated however I would appreciate some pointers around the importance of installing the piston and rod correctly before I attempt the process in future.
Thanks
Peter

Hi Peter, there are many old Briggs engines out there with worn-out rings, it is probably the most common wear problem. You'd think the aluminium bore would be a bigger problem, but it has a much bigger surface area than the rings do. I suggest you measure the bore diameter if possible, just 1 cm down from the top, to see if it is worn before spending money on new rings.

There are some especially critical points regarding re-installing the piston and rings. These are not the only things to be careful about, as you will have noted from the video you've seen, but they are extremely easy to mess up. First, do not take the piston off the connecting rod, or you will have problems putting it back on the right way around. Second, put the piston in the right way around: the gudgeon pin is offset, it is not on the centerline of the piston, and if you put it in backwards you will wear one side of the bore excessively. Third, put the connecting rod cap on the right way around. It was bored at the factory with the cap installed, and if you put the cap on backwards the two halves of the big end bearing will not match (there will be an offset in the big end bore), which will cause early failure. Fourth, oil the crankpin before you assemble the big end bearing. Fifth, clean the bottom of the rod and the top of the bearing cap and ensure there is no dirt in the joint between them, then assemble them by hand, don't pull them together by doing up the bolts. Then tighten the big end bolts to the right torque, don't just "do them up". On such a low speed, low stress engine, just doing them up is probably fine after you've used a torque wrench enough times to be accustomed to what the right torque feels like, but with a small bolt in an aluminium rod, until you get the feel of it, it is very easy to get it wrong in one direction or the other. Remember, tighten the two bolts in stages, just snugging both of them first, then bringing them up to torque alternately, a couple of Nm at a time.

There are fifty other things you have to get right, I've just focused on the ones people are prone to getting wrong.