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.