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

Have checked breather cavity, didnt look too bad in there.
I am holding off taking the valves out, I dont have a spring compressor.
I have taken valve srpings out of little engines with screw drivers.
Yes the manual I have is on a disc as a pdf file, but cant be opened without the disc in the computer, happy to post a copy to you.

So far as the valve spring compressor is concerned, my experience suggests that it is essential to use one for cars, because they have high speed engines with big valves which therefore require very strong valve springs, to prevent valve bounce. They also use split collet valve retainers rather than the keyhole retainers more common on low speed engines. When it comes to small mower engines, finger pressure is normally sufficient for the keyhole retainers they mainly use. When you get to large mower engines, say above 200 cc, you are in no-man's-land: you might get the job done with fingers, or you might end up with blood-blisters and engine parts flung violently into the distance by escaping springs. You have to make a choice: spend $40-50 on something you may never use again; or work slowly and carefully in a clean area (so you can find the bits that get ejected violently) using the spacers-and-screwdrivers approach; or make up a forked lever to use with a flat plate pivot screwed to the front of the engine.

Your main problem is that you are currently working on side valve engines, and generally, most of the available valve spring compressors will not work because the spring retainer end will not fit into the valve chest. This picture shows the type I used long ago, with a fair amount of cursing, until I finally threw it away and restricted my attentions to mower engines:


It can work on most kinds of engines - the main problem is that it is rather springy and not well suited to car engines with strong springs; it has a habit of twisting at the critical moment. I once had a massive cast iron one that worked on side valve engines only, but I threw it away too: side valve engines too large for finger pressure have no appeal to me.

So, do you have keyhole retainers or split collet retainers? For keyhole retainers, I'd try the fingers method. For split collets, I'd probably make up a forked lever, because it would probably be fun, and I'm a bit tired of hurting myself and losing the flying parts.

I'll send you a PM about the G400 manual.

Grumpy, thanks for the info on the valves.
I got valves out by flicking collar with a screw driver.
Cleaned up head.

Ok, Original engine is back in the Cox.
Engine had flywheel replaced (chewed teeth),
Cylinder honed.
New rings fitted.
New bottom seal.
Decoked, didnt touch the valves.

Report: Engine starts easily, idles and runs fine, it is not what I would call a quiet engine, still has noise - but no where near as bad, a bit loose and rattely.
It is an old engine that I have been using for many years (bought second hand aswell), I understand maintenance and have kept oil up to it ect... I have been using it on a sloping block, and have asked alot from it for what it is.

Because it became quieter when you fitted a different connecting rod and bearing shells, it appears at least a substantial part of the original noise came from the slightly damaged big end bearing. The remaining noise could be because the replacement bearing also had some wear, or it could be piston slap. When an engine is cold, I personally have some difficulty distinguishing between moderate big end noise, and piston slap. Piston slap, however, quietens when the engine warms up and the aluminium piston expands. If the noise remains the same on your engine, the remaining likely causes are:
1. Big end noise, due to a combination of a different size-grade of connecting rod, and some degree of wear to the crankpin and big end shells.
2. Tappet clearance. I tend to expect the older side valve Briggs engines to have noisy to very noisy tappets. I do not have experience with side valve Honda engines.
3. Main bearing rumble.

These three types of noise have different characters, and can be distinguished easily if you have prior experience of each.

I agree that it is unrealistic to expect an old side valve engine, rebuilt with worn parts, to be mechanically quiet. If the noise sounds like other moderately worn side valve engines, it is to be expected and should not prejudice the continued satisfactory service of the engine.

Please keep us posted on the rebuild of the smoky engine. It might be worth attempting closer clearances with this one, to make it quieter as a sort of training exercise. That would imply attending to big end, piston skirt and main bearing clearances.

Have done some cleaning & taken some pic's prior to lapping valves & honing bore.
Valve stems seem worn with side to side movement (especially exhaust), I will check them with micrometer tonight against manuals spec's.
Piston skirt has wear marks, no scratchs seen on rings.

The lateral movement of the valves in their guides is fairly important, mainly because they cannot seat well if they are not centered. (On horizontal crankshaft valve-in-head engines it is also important because oil runs down the guides into the ports, and burns.) The wear can be in the bore of the guides, or on the valve stems. The important statistic is how much clearance there is. Your valve guides appear to be replaceable, but it is usually necessary to ream the new ones after pressing them into the crankcase, so they fit the new valves correctly.

In one of the pictures of the bore it looks as if there may be a substantial ridge above where the top piston ring reaches. That would indicate bore wear. You will need to put each piston ring in turn into the top of the bore, just below the ridge, and measure the gap between the ends with feeler gauges. (You need to do this even if you use new rings: the bore is still worn even if the rings are not.) If you push each ring 1 cm down into the bore with the crown of the piston (i.e. insert the piston head-down) the rings will be at right angles to the bore, so you can get a meaningful gap measurement. Normally you also measure the bore diameter in several places with an inside micrometer, and compare this with the piston skirt measurement across the thrust faces, measured with an outside micrometer, but you probably don't have those. The piston skirt clearance can also be measured from underneath with a feeler gauge. Note it is only the clearance at the thrust faces that matters: piston skirts are diamond-turned or ground to an oval shape, with much larger clearance at right angles to the thrust faces.

That exhaust valve has not been sealing properly, and needs to be lapped, perhaps quite a bit. However first you have to resolve the stem clearance issue. The inlet valve needs lapping but has not been leaking much if at all.

Does the connecting rod size classification match the crankpin size classification? If it does, the normal procedure would be to measure the crankpin with a micrometer and compare it with the published wear limits. (Note that the pin will have worn into an oval shape, and we only care about the minimum diameter, which approximately coincides with when the piston is at top dead center. The top of the pin wears during the peak of the "hammer blow" of combustion, say about 15 - 25 degrees past TDC.) If there is wear to the crankpin, there will also be wear to the bearing shells. So, if the crankpin is worn but is within limits, in the absence of some Plastigage or an inside micrometer to measure the inside diameter of the connecting rod bearing with shells installed, it would probably be wise to replace the bearing shells. (I wouldn't replace them unless the wear pattern was worrisome, or the clearance was excessive after measuring the minimum diameter of the crankpin and the maximum diameter of the rod bearing. A big end bearing with 0.003" maximum clearance will be easily heard, and would be unacceptable even on a very old car. That doesn't necessarily make it unacceptable on a lawnmower, though.)

I have measure valves OD, yes I only have a small micrometer and verniers.
They are within limits.
A question: do I start with course paste first when lapping valves? The tube shown has cousre & fine paste.

I have thought about using the spare engines block as the valves are also within limits (much the same size) and movement side to side is not as bad on the exhuast valves stem. These images are of my spare engine.
The piston and bore I will do next.

First, lapping the valves: the coarse paste is for getting the valve and seat clean all the way around. The fine paste is for polishing them to a fine finish. The polishing part is rather time consuming and not necessarily rewarding. Provided the valve seals, it hammers itself into an even smoother finish than you can get with the fine paste. The potential issue is getting the engine through the first, say, three or four hours' running without leakage developing - if it starts to leak across the roughly finished seat, the leakage will get worse instead of better. More important than fine finishing, is getting the seat width right. The width should be even all the way around, and about 1 mm wide. Too narrow and the valve will hammer deeply into the seat. Too wide and the valve will probably never seal properly, since it won't burnish the mating surfaces.

The first consideration in choosing a cylinder is whether it has any damage. If neither cylinder is damaged, I'd be primarily interested in the bore wear. If bore wear is equal, I'd choose the one with better valve guides and valve seats. If the exhaust valve guide of that cylinder is worn, see if you can get it replaced and reamed at modest cost. Installing the guide is easily done with a stepped punch and a hammer, you don't really have to have a press, but the reamer is probably a unique size for that engine. So, if your spare cylinder's bore is at least as small as your smoky engine's bore, and its valve guides are better, I'd be using the spare cylinder.

I have used an old ring for a guide to determine bore wear.
Put the same ring in both cylinders and came up with similar gaps, around 0.75mm.

SMOKEY ENGINE

SPARE ENGINE

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.