OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Breaking Rocker arm GCV 160

Hi all this is my first post on this.

I have a GCV160 that keeps breaking the exhaust rocker arm. Its not burning any oil the valve seems to move freely. I've set the adjustment correctly. When its running it runs smooth no issues starts right up. I've checked the timing marks on the cam and the top center and that seems to be right. I would think if the valve guide was bad it would burn oil. Its only the exhaust valve that this is happing to. Any help or ideas?
Thanks
Mike

Hi Mike, welcome to Outdoorking.

It is not unusual for Honda GCV engines to break exhaust rocker arms, but there is always a reason, and it needs to be found.

When a rocker arm breaks there are two things to check for immediately.

The first is whether the valve is stuck. That is by far the most common reason for GCVs to break rocker arms, and it seems to be often associated with the engines being fitted to pressure washers. Water gets into a lot of the wrong places on pressure washer engines. A stuck valve is easily found and it will be obvious if that is the problem. Since this has been happening to you for a while and the engine has been running along the way, it seems unlikely that you have a fully and permanently stuck valve.

The second thing to check is that the valve will move as far as necessary. The valve lift is set by the camshaft and the rocker arm lever ratio, and on the GCV engines there is only one (usually plastic) cam lobe which operates both valves. Since you are not having any problems with the inlet rocker arm, chances are the problem is not with the camshaft. However, you still need to check whether the exhaust valve will freely open as far as necessary. I think the easiest way to do this, is to assemble the engine with (another) new rocker, not a cracked one, adjust the tappet clearance correctly, and rotate the crankshaft in the forward direction until the exhaust valve begins to open. Then, press down on the rocker directly above the valve, and note that the valve will open further. Rotate the engine further in small steps, checking at each step that the valve will still open further. The objective here is to see that the valve does not run out of available movement, even when the maximum lift position is reached. If it does run out of movement, when the engine runs the rocker arm will have to act as a flexible joint every time the valve opens, and it will soon fatigue and fail.

If you find there is insufficient valve movement to accommodate the full lift dictated by the camshaft, you know why your rockers are breaking and you just have to find what is causing the exhaust valve to have restricted travel. There are four obvious possible reasons. The first is that the valve guide has moved upward from its correct position. The second is that the valve has been adjusted with insufficient clearance, which has the effect of increasing the valve lift. The third is that the timing belt has jumped, and the head of the exhaust valve is hitting the piston, which limits its movement. The fourth is that there is incorrect assembly of the valve retainer, so that some part of the retainer system, or some additional component which should not be there, hits the valve guide and prevents full opening of the valve.

I know you have checked two of those four things (correct valve clearance, and correct belt timing), but if it is neither of the other two, I suggest you recheck. Then, if it is none of the four things, we are reduced to looking for unlikely problems such as a damaged or incorrectly machined cylinder head or rocker pivot, causing the rocker pivot geometry to vary when the engine is running.

Please report back when you have made these checks. If possible, include some pictures.

Hi Grumpy
Thanks for the details. I've got a new rocker arm and I will run through the checks that you've outlined. This is a lawnmower not a pressure washer. When I've put a new rocker arm on it runs great for a couple of cutting grass and there is no indication of any thing wrong until go to start it for the next round of cutting the lawn.

It will be a couple days before I can get back to you on what I find.
Thanks
Mike

Thanks Mike, it will be interesting to learn what you find. My first guess would be that the valve won't be able to open as far as it should, for some mechanical reason. If the engine has ever been overhauled, it could easily be due to misassembly in the valve retainer area (such as someone trying to fit a valve stem seal the engine isn't supposed to have), but if it hasn't been overhauled, I doubt any serious assembly errors would have happened in a Honda plant. I think part of the problem, though, is those rockers seem to be very easy to break. By the way, if you've broken a few, are you sure you didn't ever have a loose broken off piece drop into the oil pan? If you did, it is likely to get caught up in the moving parts sooner or later, and cause a worse problem than you already have.

Hi Grumpy
I off this afternoon going runs some checks as you suggested. I will let you know what I find. If I don't get back today have a happy New years.
Mike

Hi Grumpy
That didn't take as long as I thought! I think I found the problem, the valve doesn't travel very much at all. I checked the intake valve using the same procedure and that valve travels much further as I would have thought it should. Do they have the same travel length? So now what? Is there a way for me to take the valve retainer off and not have the valve fall in the engine? I'm thinking that if I keep the piston up to almost top dead center and then take the retainer off, then slowly rotate the engine so the piston starts downward letting the valve drop without falling completely inside the engine. This way I could look at the valve shaft and maybe rotate it to see if its bent or see what maybe causing the problem.
Have got any other idea's?
Thanks
Mike

Thanks for the update Mike. The inlet and exhaust valves on the GCV engines use the same cam lobe, so the only factor that could cause the actual valve movement to be different between inlet and exhaust would be if the rocker arms had different lever ratios. They are different parts of course - one is a mirror image of the other - and I don't know their lever ratios, but I doubt that they are substantially different from each other. Restricted movement of the exhaust valve is a good match for the symptoms you have observed (recurrent breakages of the exhaust rocker arm).

Because the GCV engines do not have a detachable cylinder head, the usual way of addressing this problem on conventional engines (just removing the head and dismantling it) is not available. However as you have suggested, there are work-around approaches that can at least allow you to investigate without dismantling the whole engine.

There is a trick commonly used to prevent small engines from rotating, and it can be used to hold your exhaust valve in the fully-closed position, and move it up and down slightly without damage. I do not recommend directly using the piston to support the valve while you remove its retainer, because the consequences of having it drop a bit further than you want are so severe (you would have to split the crankcase and remove crankshaft, connecting rod and piston to fully lift the valve and refit the retainer). Instead, you can remove the spark plug and slide several feet of soft cotton rope into the cylinder, ensuring that you keep the trailing end of the rope outside the cylinder so you can use it later to pull the rope back out. You might consider knotting that end of the rope so it can't go through the spark plug hole. Then you can rotate the engine so that the piston pushes the rope inside the cylinder upward until it fills the combustion chamber. (This is the reason to use soft cotton rope, not ordinary rope or cord: the cotton rope will shape itself to fill the combustion chamber without leaving voids, one of which might allow the valve to drop too far into the chamber, when you have removed the retainer and spring.) Lock the engine in that position so it will not rotate while you work on the exhaust valve retainer. Then you can remove the retainer and inspect it, the top of the valve guide, and the valve stem. You can also rotate the engine slightly if necessary, to move the valve up and down. Be very careful, though. If you allow the valve to lower itself just a little too far, and it jams in the guide, you will have to split and dismantle the engine. That is not an extremely large job, but I think it would be very annoying to have to do it just because you lowered the valve and could not get it back up.

Once you are in a position where you can move the engine a bit to check whether the valve moves freely, and whether the valve retainer and the top of the valve guide show signs of heavy contact with each other, we should be a long way further ahead with understanding the underlying problem.

Thanks Grumpy! I will get some cotton rope tomorrow and give this a try. The worst that can happen is the valve does drop in hopefully not but the reality of it all is I may have to dismantle the engine anyway to replace the Valve. Again many thanks for all your help and I will keep you up to date as this unfolds.
Mike

I'm waiting for each step like a kid addicted to a TV soap opera, Mike. Your clear descriptions are making this a useful thread, which may help quite a lot of people after the problem is resolved.

Hi Grumpy
I followed your instructions putting the cotton rope in the cylinder and it worked like a charm! I remove the exhaust spring clip and spring. I wanted to send a picture which took but not sure how to put it in this message. I found what appears to be the Valve guide all the way out of the engine to tip of the valve. I compared this to the intake and the only the valve stem is sticking out of the block (I didn't take the spring off).

What is my next step? and tell me how to put the pix in in here and I will send it to you.
Thanks
Mike

Thanks for the update Mike, we now know what is wrong and just need to fix it, but documenting the fault is very important, so we do need those pictures.

If you look at the line of icons at the top of the posting box, you should see this:


The icon you need is circled in red. If you click on it you will get this:


Click on Browse. Navigate on your computer to the first picture and click on it. Its location should appear to the left of the Browse button. Click on Add file from your PC. It should then be uploaded and a thumbnail of it will appear on the screen. Repeat the Browse and Add File steps for each additional picture, up to a maximum of ten. Then click on All Done.

The valve guide was originally driven in from above, and can be driven back in to its original position by using a generally similar technique. Honda's valve guide driver tool is special tool no. 2 in this set:


The smaller diameter of the tool is a good sliding fit to the inside of the valve guide, and the outside is a good sliding fit into the cylinder head where the guide drives in. A series of light hammer blows on the end of the tool forces the guide into place.

However we have a couple of hurdles to jump at this point. First, Honda does not authorise the replacement of valve guides in the GCV engines (though it does in the GXV engines):


The second hurdle is that you cannot use an ordinary valve guide driver to push the guide back in, because there is a valve stem inside it.

The way I would proceed in this matter, is to make a tool to suit your needs. Here are the valve dimensions:


You need to find a piece of steel bar of between 10 and 20 mm diameter, about 50 mm long, with flat ends that are square to the axis. Then you need to drill a 5.5 mm hole through it axially. It should drop over the valve stem, and rest against the top of the guide. This will be your valve guide driver tool.

The next step is to clean the outside of the guide to remove all traces of oil, using something non-residual such as iso-propyl alcohol. Paint the outside of the guide with Loctite or some equivalent product that has an extremely thin coating thickness, and will keep the guide from coming out again. Do not get this stuff on the valve stem of course - that could end badly.

You can then place the tool over the valve stem so it rests against the top of the guide, and tap on the top of the tool with a hammer, which should drive the guide downward. Watch that you don't begin to hit the top of the valve stem: if the stem nearly reaches the top of the tool, remove the tool and rotate the engine slightly to lower the valve into the cylinder. Continue driving the guide into the head until it protrudes the same distance as the inlet guide. It is to be hoped that the Loctite will imobilise the guide so it doesn't come out again. Then you can reassemble the valve spring and retainer, install the rocker arm, remove the rope through the spark plug hole, and repeat the process of rotating the engine while checking that the rocker and valve have additional movement available, even at maximum valve opening on the camshaft.

Hi Grumpy
Thanks for the info I will make the tool and get some loctite. I have friend at work that can make the tool although it doesn't difficult I think a drill press would be the best way to make this and he has one.
I've up loaded the pix I did it twice just to make sure.
Let me know if it comes through. Also in looking at the Valve it appears that there may have been a cap of some sort that went over the Valve guide with a hoe with enough clearance for the valve stem to come through. Similar to the intake side but maybe not.
I understand about being careful in tapping the guide back in as I have the piston up tight now.
It will probably be a day or so before I get back to you as I'm working tomorrow and Friday.
Thanks
Mike

Just one thing with the Loctite Mike: you will need the high temperature type, not the ordinary type. The regular stuff would be fine for an inlet valve guide but not for exhaust. (Of course the guide only came loose because of the high temperatures reached by the exhaust valve guide).

I would use a lathe to make the valve guide tool, mainly because it lets me get square ends and a straight, central hole, in just a couple of minutes. However if I didn't have the lathe I'd use a drill press.

The parts list shows a valve stem seal, and does not specify "intake only", so if there are marks from one having been on that exhaust guide, it seems your engine has been dismantled before. Here is the part:
http://www.2lcstore.com/honda-small-engine-valve-guides-stem-seals.html

I don't know the history of your engine, but it does sound as if the guide has moved up, pushing off the stem seal, and somebody has just taken off the retainer, removed the stem seal, and put the retainer back on, thus keeping the mower running a bit longer until the guide moved up further.

I was wondering if you got the picture? I'd like to see if someone posted a picture of the Valve area of a GCV160 with springs removed. This way I could tell if it did have a oil seal.
Thanks
Mike

No, your picture did not post successfully, and the HTML text which the picture uploader adds to your post, is not there. Did you see the little uploading box on your screen, after you clicked on "Add file from your PC"? After that box was on the screen for a while, you should have seen a thumbnail copy of your image on the screen. If the thumbnail did not appear, you would most likely have had a small message on the screen saying that the file was the wrong type (it has to be JPG or PNG), or that the file was too large (not more than 2.2 MB, if I recall correctly).

We haven't had a picture posted of a GCV cyinder head without the valve springs in place. However I took another look at an on-line illustrated parts list, and it shows the valve stem oil seal on the inlet valve only - see page B, below:
http://www.ereplacementparts.com/ho...ine-parts-c-37657_37658_37988_37770.html

It may be that the exhaust valve's stem runs too hot for a polymer-based stem seal to work.

Hi Grumpy
I think I got it now I forgot the add from my PC. I can take some others and send them. I think what I will do is take one of the intake with the spring off so you can post both to the files for everyone.
I wanted to tell you that I found the drill bit and I called Loctite and they are sending me a sample of 640 hi temp Loctite which should give me enough to do the job. Also while I am waiting for it to get here I'm going to remove the muffler and examine the exhaust valve stem from that angle to see if I see anything. I will take a picture of it and send it along also. I will rotate the stem to check it completely. Oh the brown stuff in the pix is just the light nothing on the stem. Everything is nice and clean. Let me know about picture if got it and what you think.
Thanks
Mike

Thanks Mike, the picture posted successfully this time. More pictures would be good - I'd like to better understand the shape of the top of the valve guide, and the matching recess in the top of the cylinder/head casting. Because the valve guides are not replaceable on that engine, I can't find pictures of the guide on the internet.

Well done on getting a recommendation (and sample) from Loctite. 640 it is only rated for 175 degrees Celsius. I keep a pack of their 620 for jobs like that - it is rated for 230 degrees Celsius, and is "For permanent assembly of shafts and bearings". However the 620 has high viscosity and requires a thick film, where the 640 can be used between press fit sleeves, which is exactly what we have here. Most likely the Loctite people were concerned to make sure you end up with a film of the adhesive, despite the tight fit between the guide and the cylinder head.

That guide has really come out a long way. Looks like we'll be relying fairly heavily on the Loctite to keep it together in future. By the way, note that 640 is a slow-setting formulation, because they want you to have enough time to press the parts together carefully before it sets - please don't run the engine in the first few hours after pushing the valve guide back into position, so the adhesive will have developed some film strength.

Hi Grumpy
Here are some more pictures. I took the muffler off and looked inside the chamber at the value shaft and it's black and appears to be gummed up. I tried to take a picture but I can't get enough light in there to have it show anything.
I'm going to use some carburetor cleaner on the shaft by using a strip of rag soaked in the cleaner to clean shaft up and the chamber to get it clean as possible. After I get the Loctite and tap the guide back down then I will go back in the chamber and re-clean the shaft.
What are your thoughts?
Thanks
Mike

The exhaust valve will not have been opening properly lately, and because of that it will have been overheated. The valve head, and valve seat, may have become somewhat burned. However if you get the valve opening and closing correctly, this may correct itself (depending on how burned it is). Because the GCV engines are a bit of a pain to work on, and especially to lap the valves (because of the integral cylinder head), my plan has been to correct the valve movement problem then run it at light load for a period, performing compression tests occasionally. It is to be hoped that the valve is not badly burned, and after a while the compression pressure will become normal. If, however, the compression pressure gets lower rather than higher over time, it would mean that the valve is burned beyond the point of recovery without lapping or perhaps valve replacement. The engine would then have to be dismantled.

I do not think there is anything you can do to clean the valve while it is installed in the engine, which will have any measurable effect. If the valve seals immediately when you install the guide properly, the crud underneath the valve head will burn away quite quickly when the engine runs under load. If the valve takes a while to seal, so you have to run it under light load for quite a while to get it to bed in, the crud on the valve may stay there during this recovery process. It is of no importance anyway, it is just a symptom of the valve's restricted movement.

Hence I do not recommend trying to clean the underside of the valve head by putting carburetor cleaner in through the exhaust port. I do not think it will shift the crud, but much more importantly, the carb cleaner is going to get into the cylinder and interfere with lubrication.

Hi Grumpy
I got the Loctite and I got a can of break clean. I just cleaned and applied the Loctite and pushed the guide back down. So I guest I will wait 24 hours before attempting to start the engine. There was no time givem for the Loctite to cure so I'll just wait 24 hours or so before I start the engine. The valve moves feely now and has good movement.
I believe you said to run under a lite load I don't have any grass to cut now anyway so I'll run it up to operating temp and shut it down and do that several times over the next month or so and see what happens. The other thing I am going to do is take a compression reading and than compare it over the next several weeks and see if it changes. It was running fine the last time I shut it down but it wouldn't restart the next time I needed to cut the grass so I knew that rocker arm had broken. That's when I start with you looking for answers.
Thanks and I will get back with you tomorrow for the "Rest of the Story"!
Mike

Thanks for the update Mike, it sounds as if the process is going well. Now we just need to learn what the compression is like, and whether it is going to be or become satisfactory.

Since you can't mow in the US winter, running it until it is warm a few times may serve to bake the loctite. When you are able to do some mowing, try to mow early and often (i.e, keep the load on the engine light by mowing short grass) for the first hour while checking the compression pressure occasionally. Then begin running it at full load, but keep checking the compression pressure until it stabilises at a satisfactory level, or it becomes clear that the compression pressure is low or falling. If the engine has run a couple of hours, some of it at full load, and the valve guide hasn't moved but compression is poor, you will have to dismantle the engine and lap the valves. If the valve guide moves, whether or not the compression is good, the repair has failed and you need a replacement cylinder block or engine.

Hi Grumpy
I put the engine back together and started it. I let run for about 30 mins and it was running fine. It started right up with no effort. After letting it run, I removed the valve cover and check the valve guide and it hadn't moved. One thing I was curious about though I looked inside the exhaust port and noticed the valve guide is protruding about and 1/8 inch inside the exhaust port. Don't if this is going to present a problem or not.
Thanks
Mike

Hi Mike,

The exhaust guide is still the same length it was when Honda made it, and the top of it is in exactly the same position it was in when Honda assembled it. All you've done is put it back the way it should be.

It is quite usual for valve guides to extend into ports. This is necessary for two reasons. The first is to get the largest possible bearing area for the valve stem, so it will take as long as possible for the guide to wear out. The second reason is that the hot gas in the combustion chamber heats the valve head, and this heat has to be conveyed to the cylinder head. The main heat transfer path is through the valve guide.

In the case of the exhaust valve there is another reason as well. The hot exhaust gas flowing through the port past the valve heats its stem even more than the combustion process heats its head. Hence it is particularly important to maximise the amount of the stem that is in contact with the valve guide. Protecting part of the exhaust valve stem from heat by taking the heat directly into the valve guide, improves heat transfer efficiency because tranferring heat from the valve to the valve guide is not very efficient: there is clearance between the two, so putting the valve guide in the way of the exhaust gas, is much more effective. Of course there are limits: you don't want to obstruct the exhaust port more than necessary, or maximum power will be reduced, and the valve is made of far more heat-resistant material than the valve guide is, so you have to be careful not to overheat the guide.

You'll find that valve guides - even the ones that are integral parts of the cylinder head - normally extend some distance into the ports, just as yours does.

Hi Grumpy
Great explanation! I think one of you replies to me you said that the engine could have been over heated. I wanted to tell you when I got the mower the whole cylinder head was incased in old grass just cake in between the cooling fins. I power washed the engine before I did anything. So I wonder if was heat that cause the whole issue with valve guide? I haven't found anything that would have cause the guide to come out.
Thanks
Mike

Thanks for that information Mike. Yes, that is just the right kind of abuse of the machine to cause the valve guide to loosen and shift, so you probably have nothing to worry about once the Loctite has stabilised. I will mention two other points, though.

First, from what I read on the internet it is not all that uncommon for GCV engines to have their valve guides shift as yours did. Of course, it may not be all that uncommon for people to let them get their cooling fins blocked with grass, mud, or whatever, so the fact that it happens occasionally to other people may not be a bad sign.

Second, when engines are severely overheated, as it seems yours has been, there are often other adverse effects. These include temporary lubrication failure due to the oil being overheated, with consequent effects on the cylinder bore and piston rings. Fixing the lubrication by removing the grass/mud and changing the oil cannot undo whatever damage has already been done.

Having issued those warnings, it nevertheless sounds very positive. If your engine doesn't emit blue smoke or use oil, and if the compression turns out to be OK, I think it will be back on track for a long and useful life.

Hi Grumpy
I just took a compression reading and its 65 psi or just a tad higher. I'm not sure what it should be but from what I can find its should be around 70. Is 70 correct for this engine? If so mine is low but that may improve as time goes on. I'm not sure how old this engine is either so it could leak a little through the rings I guess.
I will do some low load work with it when it warms up a little. Its been down right cold here in Fredericksburg, VA.
Thanks
Mike

Honda's specified compression pressure is 71 psi at 600 rpm. They do not specify a maximum and minimum for that particular engine (they do for some others) but 65 psi is close enough - it's only 8% below nominal, and within Honda's usual specification limits. For example, for the GXV120 the range is 71 plus or minus 28.4 psi. I do not think you have anything to worry about, but as always when you have worked on an engine, it is prudent to watch for anything out of the ordinary for the first couple of hours' running.

I had guessed it would be fairly cool there in Virginia. Here in Melbourne we've just had 4 successive days over 107 degrees F - a local record. Maybe we should both move to Hawaii.

Hello Grumpy
It's been a little while since I check in but I want time to see how my repairs went for both the pressure washer and the Lawn mower. I have to report good results with everything so far. I pull the valve cover on the Honda lawn mower after about 6 cuts and nothing moved knock on wood it will stay that way. The pressure washer has been happy also.
I cleaned up the weed eater carburetor had some junk in the screen now its working well. I am working on a chain saw fuel line problem hope to have it up and running tomorrow.
I can't thank you enough for the help you've provide me and I'm sure I'll be back with another project !
Mike

Thanks for reporting back, Mike. With those final reports I'll close this thread. However, please open a new one whenever you have a project you are unsure about. It is usually best to talk repair projects over when you've taken a look but haven't yet made a move to fix whatever it is. That way we may be able to reduce the risk of doing something that turns out to be unhelpful, and makes a straightforward repair into a more expensive exercise. Of course the more projects you have completed successfully, the less help you need on the next one, but there is no need to rush into going it alone.