OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Walk Behind Lawn Mower Frames Question On Scott Bonnar Cylinder Mowers Hello Everyone

Hi Gadge,

Thanks for the info on the clearances, does the manual also specify these in inches? I do know that for the points it is a 20 thousands gap.

However, I checked the B&S website and for model 80200 it says the clearances are within spec:

.005"-.007" (.13-.18mm) intake valve.
.009"-.011" (.23-.28mm) exhaust valve.

This is with the valve springs in place and the piston 1/4" (6mm) past TDC. Unfortunately, I didn't set the piston 6mm past TDC when I checked the clearances. The piston was flush.

Yup, you're correct. I stuffed up the unit conversion. That'll teach me to do off-the-cuff conversions at that time o' day!

The 6mm past TDC biz is to get the exhaust tappet onto the true 'base circle' of its cam.

At TDC on compression stroke, the Briggs 'easy-spin starting' setup actually holds the exhaust valve open slightly, to release some compression at starting RPM's. They say it has no effect on operating compression or power, at operating RPM's.

No probs Gadge. I have been trawling the internet for websites, videos (mostly YouTube) and forums for anything about 3-5hp B&S.

Today I cleaned out the ports, the valve seats and valve stems with a soda blaster in preparation for valve lapping.

Is it safe to use water or kerosene to wash down the block, ports and cylinder. In an attempt to remove any dust, dirt, soda or compound left behind?

Hot water [even boiling!], with a dash of any shampoo, is what I'd use. Rinse off with more hot water. Then blow out the nooks and crannies with compressed air.

, Shampoo? It isn't alkaline [and therefore corrosive to aluminium alloys], unlike many detergents, and rinses away very easily, leaving no residue. A trick o' the trade my motorcycle mechanic put me on to.

Thanks Gadge. Going to sand blast the block tomorrow. Will be sure to wash it down with some hot water and shampoo; before priming and painting. Been a bit busy so only managed to clean and polish the valves.

Ran out of media (garnit), so I went and purchased a 25kg bag of 30-60. The parts I needed arrived from Amazon, but bloody forgot about the piston rings. Will end up replacing them after opening the crankcase to swap over the crankshafts. Crossing my fingers because I won't know if the crankshafts are the same until this point. Pics of the polished valves.

Hey Gadge!

Can you tell me or does someone on the forum know if it is OK to use plain epoxy etch primer on an aluminium engine and then use enamel over the top. I already have a can of Hichem Super Etch Primer (grey) and went out and bought Dupli-Color Engine Enamel (Chevrolet Orange DE1620). As shown below:

hi xhall.
hi chem etch primer is good stuff but dont layer it on too thick.remember the etch primer is to etch itself onto the part not to undercoat it. its so the paint has something better to stick to.
i would recommend lightly coating it with the etch primer then try to sand most of it down before top coating with your enamel.

Hi Gizmo,

I usually put 2-3 light coats of primer on, for good coverage. Do you think I will need high heat primer for the engine block because I am worried about the paint bubbling? Also, I haven't read the back of the can yet, but do you have to bake the enamel on; such as in an oven or start the engine up to cure the paint or just let it dry in the sun?

From the looks of it the original paint job wasn't the best and I get the feeling they may have run the engine after painting. Plus they missed the whole side of the engine behind the flywheel (either to save money, time or because the cowling covers that side anyway. They painted the flywheel too.

Not sure if I should go ahead and paint the lot and put new decals on, or cover up the old ones. Need to know fairly soon because I want to proceed soda/sand blasting the cowling and fuel tank tomorrow and will prime the bare surfaces immediately to prevent oxidation.

I would not use garnet grit for blasting anything made of aluminium. It's too angular and sharp for the purpose, and tends to embed into the surface. Fine for harder metals, e.g. steel and cast iron, though.

Soda media is preferred for aluminium, or polymer [plastic] as a second choice. Glass beads are a distant third, for the reasons given above. Edit: got my threads mixed up; to quote what I said elsewhere: "I'd consider soda blasting for the crankcase, too. The problem with glass beads is that they get stuck in all sorts of nooks and crannies, especially tapped holes. And they're buggers to get out of there! If you aren't extremely thorough in cleaning them out, it only takes a couple of them to get into a bearing or such, to wreck it."

Although the local aero engine rebuilder down this way does use glass beads, there's a lot of post-blast time in meticulously cleaning out all of the blind cavities and tapped holes, in even a 4-cylinder Lycoming or Continental crankcase. I've watched it being done.

They also had a set of Lycoming IO-720 cases in the racks there [720 cubic inch, flat 8 layout], and I shuddered to think about doing this cleanout job on those.


Dunno about the temperature limit of that primer; I doubt it's up to the job on an air-cooled engine crankcase though. VHT do make a High-Temp primer, and I'd use that, or an equivalent.

Didn't end up using garnet on the block. However, I did use it on the steel fuel tank because it did have rust in some places (mostly underneath the tank) and I found trying to remove rust with soda unsuccessful. Did notice garnet getting trapped between the mounting bracket and the tank.

Just ended up purchasing the dupli color engine primer (really happy with the Chevrolet orange, it is nice and a close match to the original paint color); rather than using the hichem. I'll keep my eye out for the VHT though, next time I am at Repco or Autobarn. Going to layer on the primer and sand back until some of that pitting is filled. Looks like they used epoxy to seal the two halves of the tank where they rolled the edges over. Might fill the tank with vinegar to see if there are any leaks before commencing.

Well today I was pretty busy. Decided to slow down a bit though and check to see if the crankshaft on the green engine is interchangeable, rather than rush ahead with painting.

Well, it is indeed the same engine, they must have used the same mold to cast the newer engine block because the same mountings for the points and condenser are right behind the flywheel. The only difference is the cast iron bore, magnetron, smaller fuel tank and different sump cover.









Problem is that there is deep vertical scoring on the cylinder walls and I can feel them by running my finger nails around the cylinder. Probably needs to be honed and an oversized piston and rings fitted. I am afraid it will probably end up being used for parts.






The only thing I have to do now is get a propane torch to heat up the PTO and remove the rusted steel sleeve that was used to mount the aluminum pully.

The different sump cover is due to another substantial difference. The clue is there in the Model Number, 81232
That '3' denotes a 'Flange Mount, Ball Bearing' PTO. That's why the PTO oil seal is larger - due to the ball bearing behind it.
As it's a cast iron sleeve, it may well be OK for further service with just a good hone. Worth a try, anyway.
Yeah, rust-bound sleeves are a bit of a pain. If you don't intend to salvage the sleeve, I'd take to it with the angle grinder, and thin the side nearest the keyway, to the point where the sleeve can be split with a cold chisel. It'll come off easily then.

Hi Gadge,

Regarding the green engine, on closer inspection the scoring is not as bad as I thought. There are several marks, but they are all located on one side of the cylinder. I may end up buying a honing stone and slightly hone out the bore with my drill press. Then fit new (but not oversized) rings.

On another note. It turns out the crankshafts are not completely compatible. For the older engine with the points coil, they machined a flat onto the crankshaft. This flat is to allow a pin to rise and fall, allowing the points to contact. This flat is not on the newer crankshaft that uses the magnatron. I would have to ditch the old coil and fit a magnetron for it to work. Otherwise, of course, the points would always remain open and never produce a spark.






I have a new PTO shaft key. Should I get the clutch half that has the set screws. One screw would pin the key to the PTO (I could even notch the key to prevent movement) and then the other is at 90 degrees. The key shouldn't be able to move then. In this position (past the notch) it is still a tight fit.

Isn't there a Magnatron already on the more modern engine? Why not just fit it to the one you are putting the crankshaft into, or just use the complete later model engine?

The set screw clutch half is the only one available new; it superseded the 'captive cotter' type long ago. It is also much less trouble-prone.

I'd just get that sleeve off the crankshaft of the late model 'green engine', and rebuild that one. It has 'all the fruit', as regards good options which are available in a Briggs.

The only better option, would be to fit a new genuine Honda engine.

LOL! I'd love a new Honda, especially since this rebuild is turning into a nightmare. All because of that mangled keyway.

As it turns out, the shaft diameters next to the timing gear are not the same. They reduced the diameter to fit that bearing.

Dammmm!!!

I am really pissed, but will have to endure because I have already spent $$$ getting new parts, tools etc.

dont they make different size clutch halves for just such an occasion ? gadge might or deejay sure would know

Yes, the engine side clutch half is available for 5/8" and 3/4" shaft diameters, at least. Deejay would know of sources for other sizes, if any exist.

Electric motor reconditioners commonly offer keyway repair services [weld and re-machine]; it would be worth calling a couple, since you have the damaged crank out of the engine. Not much different to working on a leccy motor shaft, really.

That sounds like an great idea Gadge. BTW, this is what I mean about the PTO. The end of each crank is still the same (5/8").



...and inside the covers.