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

Hello
I am trying to get my old cream bonnet Cox ride on ready for summer.
Its GV400 engine has developed a knock which gets louder under load.
I have removed the engine & have it mounted ready to pull down.

I have bought a second hand GV400 ( blows smoke & hard to start ).
I also have another one I bought in pieces.

I have purchased a gasket kit & 2 sets of rings.

Would be happy to have one running out of the 3, then work on one as a back up.

After that back story, my question is what would cause the knocking under load? Should I start on this or rebuild the smokey engine.

We would have to hear the knock to be reasonably sure, but the usual cause of an engine knock on an engine that has not been dismantled in a long time, is a worn big-end bearing. Big end knocks do tend to be louder under load, though you can usually hear them at any load. In general, big end bearings only fail on correctly loaded and correctly assembled engines if there is a failure of lubrication. That, in turn, usually happens because the oil level is low, or the machine is run on an excessive slope, or a combination of the two. Once slack develops in the bearing, it will usually get worse fairly quickly if the engine is run under load. Repair is usually possible, requiring at a minimum, replacing the connecting rod, but usually there is damage to the crankshaft as well. If you choose to repair the engine before the connecting rod breaks, it is usually not especially difficult, but if you continue to run it under load the rod will probably break, and it will then be doubtful whether the engine is economically repairable.

The owner manual for your engine is available here:
http://engines.honda.com/pdf/manuals/3189120.pdf

Unfortunately your engine is one of a relatively small number of Honda engines for which no workshop manual seems to be available on-line.

Mark, I didn't really answer one of your questions, because I haven't seen the bits and can't judge their condition. However I'll tell you what I would do, to get the mower back into operation with a good engine, and a good spare engine backing it up. I'd remove the cylinder head and crankcase cover from the engine with the knock, remove the big end bolts, remove the piston and rod, and inspect the crankpin and the big end bearing in the connecting rod. If I found scoring and wear in the rod but the crankpin was unmarked, I'd reassemble the engine with the connecting rod from the spare engine. I'd use either the original piston or the spare one, whichever was in better condition, and I'd fit one of the sets of new rings. I'd inspect the valve seating and probably lap the valves and adjust the tappet clearance (by swapping the spacer bits or grinding the end of the valve stems). The engine would be back in the mower within two hours. Then at my leisure I'd open up the smoky engine, clean the bits, inspect and measure them, swap pieces from the spare engine to get the best outcome I could, lap the valves, fit new rings, and put it back together as a decently overhauled engine. I'd only throw away worn or scored bits, keeping the rest of the spare engine as future spares.

Thats awesome advice Grumpy, I have started dismantling the smokey engine and have done some cleaning. The exhaust which was covered by a plate, I know why now, I will describe as not good.
Will upload pics as I go to share my experience.

Mufflers are one of the most failure-prone parts of internal combustion engines. Just be glad you are not living in the days of leaded fuel. The Tetra Ethyl Lead (TEL) is transformed into metallic lead during the combustion process, and lead being a conductor, this was a problem when it deposited itself on spark plug insulators. To overcome the problem, TEL was always packaged with "lead scavengers", extraordinarily corrosive chemicals, mainly halides and bromides. The halides and bromides ate exhaust systems. In those days, cars used to require regular replacement of mufflers, and even exhaust pipes.

Thank you for the offer to keep us informed as you investigate the condition of your three engines, and hopefully turn them into two good ones. The usefulness of these threads to other members depends on them incorporating clear, relevant photos like the ones you have posted above.

G'day
Have piston out & am inspecting cause of knocking under load.

That engine has replaceable bearing shells, it doesn't have an aluminium connecting rod that serves directly as a bearing material. Presumably the connecting rod is steel. Most likely you do not need to replace the rod, just the bearing shells. The upper shell looks as if it has worn through its babbit or trimetal layer, in the center.

I can't judge so far whether you have a problem with the condition of the crank pin. There seems to be some scratching in the center, in the area that has been in contact with the backing metal of the bearing shell, but I can't see whether it is serious. If you can feel any roughness or striations around it, or detect any circumferential scratches, it would be better to use one of the other crankshafts.

How many hours has the engine run? So far it looks more like a worn out bearing than an abused one.

The cause of the knock from a big end bearing is slack. The most accurate way to measure the slack is with a product called Plastigage. It is just a piece of small diameter plasticene-like material. You put a bit of it in between the connecting rod and the crankpin, and assemble the big end, torquing the big end bolts to the correct tension. Then you disassemble the bearing and check the width of the squashed piece of plasticene against the gauge that comes with the kit. It tells you how many thousandths of an inch of clearance the bearing had. From memory (big end bearings seldom wear out these days) you can hear annoying bearing rattle at 0.003" clearance, and if you have much more than that it sounds as if it is about to break something. It is impossible to maintain a proper oil film in a loose journal bearing, especially with splash lubrication.

Incidentally I see the engine has a pair of counter-rotating balance shafts, to reduce vibration. The larger single cylinder Briggs engines tend to have either a reciprocating weight, or a pair of shafts, to do the same job. Large single cylinder engines produce considerable vibration unless you do something to counteract it.

Thanks for your words & time Grumpy.
I realise it is hard to comment from your distance.

The images below show the 2 pistons, the bottom one is my spare.
The connecting rods are mumbered differently, not sure about that.

The image of the bearing shells are off the spare aswell.
They are damaged/marked as you can see.

I used my finger nail to try & pick up scratchs on the crankpin.
It was smooth as a babys you know what in places, but I did feel ever so small grooves with my finger nail in other places.

Think I will buy a new connecting rod.

Mark, the bearing shells can easily be pushed out of the connecting rod, either with the point of a knife or sometimes with the tip of a screwdriver. They are only held in place by the slight springiness of the steel backing of the shell, and the small tang at one side of one end of each shell (just above and to the right of your thumb in the last picture). Replacing the connecting rod is unnecessary unless it is defective - normally you might or might not replace the bearing shells when you put an engine back together, but at this point I am not sure I see clear evidence of enough wear on your mower engine's big end bearing to cause a significant noise. The wear pattern on the upper shell of the engine from your mower is assymetrical, indicating a connecting rod misalignment, so it would be worth while using the other rod in that engine. Correcting the misalignment by bending the rod is possible but not recommended for the inexperienced. I also see you have steel rail oil rings, which seldom wear enough to pass oil in any normal lawnmower's lifetime. We should now look for other causes of your knock. One possibility is a loose pulley on the crankshaft extension - the double pulley that drives the blades and rear axle. Another possibility is a problem in the cutter shaft bearings. As I said, without hearing the noise it is a bit difficult. Did the noise occur if you revved the engine with the cutter and wheel drive clutches both disengaged?

Why didnt I think that it may have been something other than the engine.
Yes, I will try and source just the big end bearing shells. I would like to see new ones there.
I didnt know about the oil rings.

The ride on is 150km away, I have just the engine here, I seem to remember the knock both engaged & disengaged.

For now I have reassembled that engine with the spare rod & piston, I honed the bore & replaced the rings.

Tomorrow is another day, I will finish reassembly and test run on a bench, and then start on the smokey engine.

I think you have done the right thing, and there is a good chance you have fixed your knock - I can't tell from the limited evidence that has been posted. I'll try to clarify what is going on, Mark. Look at the upper shell of the big end bearing of the rod that was in the mower. It appears to be worn through to the backing on one side, and the wear pattern does not even reach to the other side. This means the connecting rod is bent: the gudgeon pin hole (or little end) is not parallel to the crankpin hole (or big end). As a result big end lubrication has been a bit poor, and equally importantly, the contact force has been concentrated on the outer edge of the bearing shell, causing excessive bearing pressure, and physical contact with the crank pin at times, leading to wear. Compare this with the bearing shells of the other engine: the wear pattern there is just about ideal, except for not extending all the way around the shell. In other words that rod is not bent. The bearing may have done a lot of work and gradually accumulated some normal wear, but it is still a healthy bearing.

What we don't know, is whether the failing, unhealthy bearing that was in your mower engine, has already generated enough slack to be making a loud noise. The only way to find that out would be with Plastigage: because the rod bearing has now worn tapered due to the misalignment, it isn't completely practical to measure it with a micrometer. So, you have made the right move by replacing the bent rod with the straight one from the other engine, and temporarily using the bearing shells from the other engine's rod. (They were already in the rod, and are therefore now in the engine.) If your knock was from that worn, tapered big end bearing, this should fix it. If the knock was external to the engine, of course it won't fix it, but you will still have fixed a significant fault in the engine. One day, when the engine is in need of overhaul, you could fit new bearing shells, but it doesn't seem an urgent issue to me. Now you can start the engine, and see if it runs properly and quietly. If it does, but there is a knock when you put it back on the mower, then you can find the external problem causing it. In the meantime, while isolating the cause of the knock you will also have fixed a developing problem in the engine, so your time has not been wasted.

To get the smoky engine ready for service you need a good rod for it. I suggest you should not fit the bent one from the original engine. If the bearing shells are still in the rod from your remaining engine, you can check the wear pattern and see how it looks. You might post pictures of the shells here: it will improve this thread, and who knows, we may be able to help you figure out how things were going in that engine during its lifetime.

Thanks, great stuff.
Have researched bearing shells to add to this thread. (you must get the right ones).

Engine fired first start & ran fine, no load, nothing unusual heard.
I wont be able to fit this engine to ride on for a while, to test it under load.
I will report back in with results when I do.

Thanks Mark, it sounds as if at a minimum, you have extended the period until that engine will need an overhaul. If the mower is now quiet, you've fixed your problem. Are you going to overhaul the smoky engine right away, or put it aside until you've got the mower working again? If you overhaul it, it will be useful to this thread to show us what the big end bearing from the spare parts engine looks like, and whether you decide to use it to build your spare engine.

Have started to strip engine that was hard to start & blowing smoke.
Do not know the history of this engine.
I would like to try & breath some new life back into it.
I have a new set of rings & some gaskets, life is good.

The bore seems to have some vertical marks, which might suggest that the engine has been run without an air filter. It doesn't look too serious, but the marks will need to be honed out and of course the rings replaced. The piston may have matching marks, which doesn't necessarily matter much. Are these old pictures? I thought you put that connecting rod in the engine with the knock and the misaligned rod?

I suggest you take a look at the valve seats, since it was hard to start. It's easier to do these things while it is in pieces.

Grumpy, no these are not old pic's, The con rod & piston I used previously were out of my spare engine that was in pieces.
This is a complete engine that I have opened up for the first time today.
I have heard it running when I bought it, it blew black smoke & was started with a small spray of assist.
I will check the rings for matching scratches.
I will hone the bore & replace the rings.
The valves are another story, I have only just got a lapping stick & paste, I have watched a few U tube videos, thats the extent of my experience here.
You might find it funny but I had to google "crank pin" this weekend because to me its not a pin.
Here are the images of the smokey engines bearings to compare.
Great stuff, I set aside this weekend to sort out these engines so I dont have to push my super 24inch 2 strokes as much this spring, I will be able to sit down & mow.
Thanks for your words & help this weekend, another week of work & I will attack this engine again.

The wear pattern on the bearing shells looks nice, they should be good to go back in. The exhaust valve seems to have been leaking a fair amount, and the intake valve seat has black areas too, so they both need lapping. Remember, the most important objective when lapping is to ensure that no trace of lapping paste gets on the valve stem and finishes up in the valve guide: that would ruin it immediately, and cause a problem.

The balance shafts, and of course the camshaft, have to be timed correctly when you put them back in. There are timing marks on all three gears in the balance system (the one on the crankshaft, and the ones on the ends of the balance shafts). There should also be marks on both camshaft timing gears (one on the crankshaft and one on the camshaft gear). Don't feel certain there will be, though: I have a GXV120 that had no timing mark on the camshaft gear. Fortunately I checked before I dismantled it, and made my own mark.

Note that black smoke is not oil smoke, it is petrol smoke caused by rich mixture. The engine does seem to have been burning oil, though, by the look of the top of the cylinder in your pictures. When you take the piston rings off the piston, you can check the ring gaps to find out how worn they are. We can talk about that when you get that far.

I hope you have a productive week at work, and come back ready for more fun.

Have done some cleaning, bottom of crankcase had thick black silt.
See image of timing marks for this thread.

Mark, if you examine that black "silt" I think you'll find it consists of particles of metal that have worn off various moving parts, coated with goo that used to be lubricating oil and/or carbon sludge that has blown past the piston rings. Regular oil changes usually remove most or all of it, provided you always warm the engine before changing the oil, and if possible, tilt the engine while draining it. (Some people use "flushing oil" to help clean up in there: they put a mixture of oil and kerosene or diesel fuel in the engine in place of oil, start it, and run it at idle with no load for less than a minute before draining it. It can be very effective in washing away the rubbish, but I worry about the residue of diluting agent that stays behind after draining the stuff.) You should take a look at the breather system, especially the Positive Crankcase Ventilation valve (behind the flywheel on the small OHV Hondas I am used to, or in the valve chest cover on the side of the engine for a side valve Briggs). When an engine has oil consumption it usually has blow-by, which pressurises the breather system by blowing crud through it. The gas makes it through into the engine's air intake, but the crud often parks itself along the way.

Thank you for posting the instructions for timing the camshaft and balance shafts. It looks as if you have a workshop manual for the GV400, or at least for a G400 - I can't find a free supply of either on the internet, so you are well ahead of me.

Don't forget you have to adjust the tappet clearance after you lap the valves, because they will sit a bit deeper in the valve seats, reducing the clearance.

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