OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Rebuild project HONDA GV400

That is around 0.030", which is at least double what a new ring and bore would give, but less than the service limit. If the ring you used was a top ring, those are usually chromed on Honda engines, and don't wear much. If it was a second ring, it is a remarkably small gap for an old ring. Anyway, both cylinders are the same diameter, and neither is worn out, so it seems to me you might as well use the cylinder with the less-worn exhaust valve guide. Of course you should use new rings, and measure the gaps by trying them in the bore of the cylinder you intend to use.

Next step is to measure the crankpin size and ovality.

Ok, have looked at how to use Plastigage, just have to get some.

Grumpy I used an old top ring to get 0.75mm.
I used a new top ring and measured 0.5mm.

My micrometer only goes to 26mm, best crank pin measurement I can get is 37mm with my verniers, no matter where I measure.

Mark, I think you know we need more precision in these measurements. A 0.5 mm ring gap is 0.020", which is not very flash at all for new rings in a good bore. I put new rings in a well-worn (0.007" bore wear, compared with a service limit of 0.010") GXV120 a couple of months ago and the gap in a new top ring was 0.015". So, it sounds as if your bore may be fairly close to the service limit for wear.

Measuring the crankpin at "37 mm" does not get us anywhere: you need micrometer measurements, or Plastigage. Remember, we need to measure the maximum clearance, and that will be with the crank 20 degrees past TDC, and with the Plastigage across the bearing in line with the centerline of the rod.

Hello again, I have a larger micrometer I can use next week to measure crankpin.
Am coming to the conclusion that the best cylinder needs to go out for rebore & valves seats and wondering if that is viable.
Cheers

It is the valve guides that need replacing, not the seats. The cost of those jobs depends on who does them, but sometimes the cheapest operator does not do the best work. If you go to a Honda dealer I think that work could cost quite a bit more than a second hand engine in decent condition (either Honda or Briggs). I think most people would hone the bore to 0.010" above standard size, buy an oversize replacement piston and rings from Thailand in a package deal with gaskets, big end shells, and a few other bits, and put it back together. The valve guides may be OK, you can check by measuring the movement of the valve head when you wobble it in the guide. If you don't have a dial indicator to use for that, you can do it by clamping a block of metal to the cylinder's top deck then measuring the distance to the nearest point on the valve head with feeler gauges, at both ends of its lateral movement in the guide. Do that in the direction of greatest movement, of course. If the exhaust guide is excessively worn, you can replace it yourself provided you can find a suitable reamer at a good price. You could try ebay for that.

Ok, I can measure valve guide play.
I have stalled a bit with this & lost some momentum, it is up to me to do some research now.
Thanks for your patience, I am keen to learn & have learnt alot.
I used to think 1mm was small.
I can also transfer these skills to smaller 4 stroke engines.
Cheers

Hello,
A month has past, I have put the engine back together with new rings, I used the best cylinder I had out of the two, they both had bore wear with one having better valve guides.

It was uneconomical for me to get new guides, oversize cylinder rebore, piston & rings & I wasnt prepared to do it.

So the results:
Well it started easily and ran nicely but was smoking badly.
Because I live in the suburbs, I shut it down pretty quickly.

I decided to run it up at the property where there is no one to annoy.

The smoke was from oil in the muffler and poor tuning.
So I have given it a good run, it is smoke free & quite a quiet engine.
There is a bit of noise there. I cant pin point it.

I will fit this to my 2nd Cox ride on, its Briggs 12.5 quiet has issues, caused by me over working it.

I have been using the 1st engine from this thread, stil lgoing OK, just have to wear your ear plugs.

Did you check the tappet clearances? Excessive tappet clearance can cause quite a bit of noise. It is useful to find the source of odd noises, even if you don't fix them - some of them are signs of impending doom, while others just indicate the engine needs maintenance.

Heavy smoking immediately after replacing rings in an engine that was smoking heavily due to ring wear, is normal. The exhaust port and muffler will be full of oily crud, but this will burn out in normal service within an hour. It is a bit unsightly and embarrassing, but burning it out that way is usually the quickest, cheapest and least-damaging way to clean out the port and muffler.

Aside from the question of odd noises, your engine should now run pretty much like a good one for one third to one half of the hours it had run up until you overhauled it. By the time it wears out this set of rings and smokes again, the bore and valve guides will be in hopeless condition and you (or the next owner) will have to choose between a larger overhaul, and scrapping the engine.

G'day Grumpy,
Yes, I lapped both valves and adjusted valve clearances as diligently as I could, as this is something I felt I had some control over, unlike an over sized bore.
I will listen to the noise again, next time I go up there. (hard to descibe noises in text)
These two rebuilds have given me invaluable experience and in my mind, was not a waste of time. I call it all practice.
I now have two working engines, even though they are less than perfect.
Thanks.

If I recall correctly, both engines now work well but make noises you don't care for. In the case of the first engine, it seemed likely to be a big-end knock. The second engine's noise you haven't described.

There are some characteristics of the noises you could identify, and perhaps these would suggest the cause.

One of the most common and least serious noises has the character of rattling tinware. It is usually caused by the cooling air cowl and/or the recoil starter hardware moving about or touching something.

Another common noise is a clack rather than a rattle, and happens precisely regularly in proportion to engine speed (at exactly half engine speed, perhaps from each of two different sources with different intensities). That is a side-valve tappet clearance noise, and is caused by those low-cost engines not having a "silencing curve" on the camshaft such as car engines use. After verifying that the clearance is actually correct, it can and should be ignored.

A less common noise is a tap rather like a big-end knock which occurs at engine speed and may be intense when the engine is cold-started, but fades as it warms up. That is piston slap, caused by excessive piston skirt clearance, and within reason it is of no consequence beyond being embarrassing in the presence of other people, who form negative opinions on our mechanical prowess when they hear it.

There are also two types of tap or rattle that occur at engine speed but do not change with warm-up. One of them can be of any intensity from a very light tap to a heavy thump. That is caused by excessive big end bearing clearance, and if it is of the heavy thump variety it should be cause for serious concern. The other tap or rattle is always quite light and is only of concern if we mistake it for a slack big-end. It is actually a gudgeon, or little-end, sound due to a poor fit between gudgeon pin and piston, or gudgeon pin and connecting rod. As long as its intensity is within reason, like piston slap it is again a social problem rather than a mechanical one.

Aside from these classic noises there can be rattles or taps due to relatively minor parts of the engine being loose or misaligned. My usual concern with those is whether they have recently arisen or have been there for years. If they have just begun they are more of a concern than if they have been there for years.

Grumpy, that is fantastic, I will write these noises and symptoms down and take with me tomorrow, as we have 4 wonderful days at the block.

I will use these engines carefully and monitior engine noise, because if I dont the alternative is pushing a super 24 around.

Will report back on return.

Grumpy and Mark thank you for this post it has been excellent.
I have an old Masport Commercial Slasher mower that was given to me with a Honda GV400 motor that was in need of a little TLC.
I opened the motor up to find the main bushes had turned within the conrod. Luckily the crank was not damaged and neither was the conrod. I tried to purchase bushes but Honda do not sell them anymore only a Conrod with the material built into the Rod. I purchased a new Conrod from Sparesman in Thailand and have started to reassemble the motor.
I followed your timing alignments for all the cogs which worked perfectly. However I am bewildered with the internal u shaped lever in that which position it should be in when putting the casing back on. I realise it is something to do with the little weights and the slide piece but not sure what it is supposed to do?

Hi DDJJKK, welcome to Outdoorking. It is best to post a picture of the part when you ask a question like that, otherwise we have to guess. Here is the assembly diagram for the last bits to go into the crankcase:



If I were to guess, my guess would be that you are talking about the Governor Arm Shaft. If so, the diagram shows which way it goes on. Please post a picture so we can be sure we're all on the same wavelength though. Also, Mark may make a different, and probably better, guess than I have.

The governor has a pair of weights on the timing gear. As the engine speed increases the weights fly outward due to centrifugal force, and the levers on the weights push a sliding plunger along the shaft. The fork on the governor arm shaft is pushed by the sliding plunger, causing the governor arm shaft to rotate. Outside the crankcase, the far end of the governor arm shaft has the governor arm clamped to it. Thus the governor arm moves when the engine speeds up.

Spot on Grumpy thanks for the diagram. I will post a picture next time as well yes it was the Governor Arm Shaft and I have installed it incorrectly so will rectify on the weekend and then complete the rebuild. I will post a picture of the completed engine and Masport mower once completed hopefully as clear as Marks which have been excellent regards Dave

Grumpy and Mark thanks again for your post and help I now have a working Masport Walk Behind Slasher Mower with a like new at least internally Honda GV400 motor no smoke no noise just works.
Dave

Thanks for reporting back, Dave. A thread with an ending is much more useful in the archives than one that tapers off into a mystery - especially when the ending is successful.

I'll close this thread. If anyone needs to post to it, just send a PM to a moderator.