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

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.