OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Honda GV400 flywheel removal

I have a GV400 on a Deiutscher mower which has given great service, but which now will not fire up at all. There is suction at inlet port. Both valves are functioning. Spark seems to be intermittent, and weak. I think maladjusted points must be the problem??, but cannot remove flywheel. Is the nut holding this flywheel right or left-hand thread? Wheel rotates clockwise. I cannot find a serial number, so am not sure of this points and condenser or not. Suggestions please.
Mac_Cullum

I think you will find all Honda engines have the flywheel retaining nuts held by right hand threads. Because the flywheel is on a key, there is no advantage in having a left hand thread. Also, the main issue here is if the engine stops suddenly due to having hit a waterpipe, in which case the flywheel moves clockwise and tightens the thread. In any case you can normally check the thread since the crankshaft protrudes through the retaining nut for at least one turn of the thread.

I agree that on an ancient engine which has gradually lost spark intensity, there is a good possibility that the problem will be that the points have closed up. (The points gap would have to be down to much less than 0.010" before this would happen.) However it is fairly difficult to judge weak spark conclusively unless there is a standard sparking test that you have been doing over the years and now find the machine cannot pass, whereas it did pass the same test previously. Briggs have two such tests: a 0.060" spark gap, and a 0.166" spark gap. Honda does not have an equivalent test. I suggest that before pulling the flywheel you try a 0.060" test gap external to the engine, in place of the spark plug. If it will not spark evenly across that gap, it is unlikely to fire the mixture consistently with the standard plug gap. In the limited testing I have done, Honda's electronic ignition at least, will not fire across a 0.166" gap, and it is not a good idea to try it because it tends to be hard on the electronics. The tests I have done on a Briggs engine fired well across the 0.166" gap, but when I tried it in series with the spark plug on a running engine, it stopped firing after just a few seconds. See why I don't want to do a proper test series on a Honda, given the prices of their spare parts?

Thanks Grumpy, I will follow your advice ASAP. Is the B & S external test a standard gadget, or do you mean just a new plug set to that gap? Sorry if I seem very ignorant, but I was trained as a surgeon, and so lack practical experience with engines.

Hi MacCullum, you can buy a gadget from various auto shops that is made for doing the spark test, but there isn't much technology involved, and the home-built product is always more fun while suiting your own preferences. Here is mine:


It consists of an old car spark plug that had earned honourable retirement, gapped to 0.060"; a 14 mm nut; and a 4 for $2 Taiwanese spring clamp. It is best to use a real spark plug rather than a tester based on a fake spark plug, because you can't adjust the gap on the fake ones, and the gap is too big for general use on lawnmowers (it's intended for cars with high energy ignition, and is over 0.100" gap). The tester Briggs and Stratton supply has a fixed gap of 0.166", and is even less suitable for general testing (but it is rather cute):


If you make your own tester, remember that spark plugs have a 14mm diameter x 1.25mm pitch thread. Common or garden 14mm nuts have a 1.5mm pitch thread (metric coarse) or 1.0mm pitch thread (metric fine). You can fix that by installing the plug into the nut with a fair sized spanner, since it will never be removed and doesn't need to hold any load anyway. Alternatively you can find the right nut. I cheated: I bought a 14x1.25 tap and reworked the nut, but the big spanner solution is quicker and equally effective if you don't mind ruining the spark plug (you could weld it to the clamp if you wanted to, and eliminate the nut. I think most people use a bent piece of tin around the metal body of the spark plug and screw the piece of tin to a clamp, to avoid both the welding and the nut issues.)

With the simple-style tester you just attach the spring clamp to a metal part of the engine, and attach the spark plug lead to the tester's spark plug in the usual way. Remove the ordinary spark plug from the engine so it will spin easily when you pull the starter.

Incidentally at least some of the GV series engines had electronic ignition, so if your spark is erratic you may be up for a new ignition module. However, first test the spark. If it is defective, you will need to do a couple of standard service checks to see that the module is properly grounded, and it has the right resistance values.

Thanks a lot Grumpy, I will let you know how it goes. MacCullum

I'll look forward to the next installment. Remember, if the spark is bad, post a picture of the ignition module before taking the flywheel off. It probably has electronic ignition, which might mean you need a new module - see final sentence of my previous post. There is no point in removing the flywheel if the ignition is electronic.

Lo & behold, spark at .060" excellent. I presume I was in too light an environment, or checking by myself holding plug on frame, and had poor contact; sorry about that! I do not see any gap between tapper and shaft of valve, but I suppose tappet will not move beyond contact with valve unless pushed down onto cam by ? A screwdriver ? The feeler gauge. Gap for inlet should be between .002" & ..005". These feeler gauges seen very flimsy. Should I just try to push them between valve and tappet?

Checking spark in direct sunlight is always pretty difficult. With a Honda electronic ignition I find I can't really see the spark that way, but I can hear it click as it arcs.

The tappet clearance is critical, and is often neglected with side valve engines like yours because it seems to change so little. Over long periods the valves may tend to pound their way into their seats, which decreases clearance. If it decreases very much from what it should be, the valves will not be able to seal against their seats, and will burn, resulting in hard starting and low power. The valve clearance on a side valve engine exists without you having to lift or push anything: the tappet should not touch the valve stem, the full clearance should exist statically so long as the engine is in the correct rotational position.

Check the tappets on that engine by rotating the engine until it is just past top dead center on the firing stroke, then carefully slip the correct size feeler gauge between tappet (i.e. cam follower) and valve stem. If you think it is difficult with a side valve engine, don't try it with an OHV engine where you have to work with the feeler gauge curved, yet still get a sensitive feel for how much pressure is being applied. Lawnmower engines have very puny valve springs, and you can quite easily force the feeler gauge into a gap that does not even exist, just by pushing on it. When there is some slight clearance, you can easily be fooled into thinking that there is "hardly any" drag on the feeler when in fact it is lifting the valve off its seat: those springs are really weak and don't press very hard on the feeler. Too little valve clearance is much worse than too much, as far as damaging the engine is concerned. Remember, the test is performed with the engine cold, but because of metal expansion the clearance usually decreases as the engine warms up - especially for the exhaust valve, which is very hot indeed when the engine is running. Because of this the specified "cold" clearance for the exhaust valve is usually greater than for the inlet valve.

My method for checking lawnmower engine valve clearances is as follows. Take a gauge that is mid-way between the minimum and maximum thickness for that valve (inlet or exhaust) and see if it will slip between tappet and valve stem without touching: very, very free-sliding fit. Then take one that is 0.002" thicker and try that. I expect zero resistance from the nominal one, and mild tightness from the over-thickness one.

All this is different from checking the valve clearances on a car, where there is no chance of sliding the feeler around if it is lifting the valve: cars have relatively massive valve springs. Checking lawnmower clearances gives you a chance to practice that surgeon's touch.

Inlet valve is .005, which is on upper limit of recommendation. Exhaust is .017", which is .011 above upper limit! I am tempted to replace carby etc and look for a problem in fuel supply side, ? Water??, but should I lremove head and lap exhaust valve first? I fear this thread is going to end up as a complete manual on repairing small engines. Sorry

You have at least enough tappet clearance, which in itself is good news, but either some amateur has tried to adjust the exhaust clearance and made a mess of it, or that valve is not closing fully. It would be a good idea to do a compression test, because that will give you quite a bit of information immediately. However if you don't have a pressure gauge and don't want to get one, you could remove the cylinder head and inspect the valves and valve seats. Healthy valves and seats have smooth, light or metal coloured seating areas. If that exhaust valve has a black seating area, and a black seat, it is not sealing and needs urgent attention. Removing the cylinder head is not wasted effort, because either the exhaust valve needs lapping or you need a new exhaust valve, one or other must be happening to cause that monstrous tappet clearance. The advantage of doing a compression test is that you could then repeat it with a spoonful of oil poured in through the spark plug hole, and we would know whether your piston rings are leaking.

Do not worry about the thread getting into detail, the detailed how-to threads are the ones that are most popular in our archives, and we have very little archival material at present on side valve Honda engines.

I am at Cape Schanck at present, and could go to Rosebud or Mornington, but tomorrow am going to Melbourne near Pakenhan and Dandenong. where can I get a suitable pressure gauge, and what sort/ brand? while I am on the job I would like one which would also work with 2 stroke engines. MacCullum
Maybe Outdoor King could supply?

A compression tester consists of a pressure gauge, a non-return valve, a pressure release valve, and an adaptor to allow it to be connected to a spark plug hole. You can get one at just about any automotive shop. Some come with a rubber cone that you press against the spark plug hole, and others have a flexible hose with a spark plug thread on the end of it, so you screw the fitting into the spark plug hole. That kind seems more favoured by professionals than the rubber cone type, because it is easier to use single-handed: it can be a bit of a challenge to spin the engine whilst holding the gauge against the spark plug hole with one hand. There should be instructions with the gauge - it is simple to operate but there are hints as to what various odd readings mean.

I currently use a Ryco one and it seems satisfactory. For decades I used a plastic American one that cost about a tenth as much and gave the same results. I think I finally threw it in the skip after I inherited the new Ryco one.

hi Grumpy, best compression I can get on a strong pull is 55psi.. I had a piece of kitchen paper keeping dust out of inlet port, and this blows out when engine cranked. This would seem to indicate a seriously leaking inlet valve, I presume?
Will oil in cylinder test work on a horizontal cylinder??

If you have a piece of paper across the inlet port, the flow of intake gas will be restricted and you will get an artificially low compression test reading. A paper funnel which leaves the port itself open, on the other hand, should do no harm.

A slight flow of gas outward from the intake port at the beginning of the compression stroke is unavoidable because the intake valve cannot close instantaneously. It begins to close late in the intake stroke then finishes the job early in the compression stroke. When the engine is running this has little effect because of the momentum of the gas moving through the carburetor and port, but at cranking speed a backward puff can be observed.

I suggest you repeat the test ensuring that the flow of intake gas is not obstructed, then repeat it again with the spoonful of oil in the cylinder (through the spark plug hole). The horizontal cylinder has little effect on this test: the oil is initially at the bottom of the cylinder, but it is swept upward by the piston and rapidly circumnavigates the top piston ring, trying to find a way past the ring.

Do you have the GV400 workshop manual? The only ones I can access on line are the 100, 150 and 200 cc side valve engines. Specified compression pressure for the 100 cc is 30-60 psi, and for the 150 and 200 cc is 85 psi. (The 150 and 200 have 6.5:1 compression ratio, compared with 5.6:1 for the 100 cc).

Pressure without oil 50psi; After oil in cylinder 75psi.
I have not been able to find a workshop manual for the GV400. I can't even find a parts list on the Honda website.

Unless you put a rather large amount of oil in through the plug hole, it seems your piston rings are worn considerably. Has the engine been smoking and using a substantial amount of oil?

Here is the abbreviated workshop manual for the GV150 and GV200, which hopefully bear some resemblance to your GV400:
http://www.honda-engines-eu.com/en/images/1004.pdf

I suggest you have a look through the manual and decide whether you want to overhaul your engine. If it is not smoking badly, it can probably be made to run fairly decently without an overhaul, and we can discuss that.

Are you certain your normal spark plug is clean and is sparking properly? If you are sure of that, the next step would be to check whether the engine has a fuel supply problem. This can be done by putting a spoonful of petrol in through the spark plug hole, installing a reliable spark plug, setting the controls in the fast run position (no choke), and pulling the starter several times. If it starts and runs briefly then stops, your problem seems to be in fuel supply, and we can talk about how to overcome that.

I can certainly lap the valves, and replace the exhaust one if that proves to be necessary.
My only problem with that is that I would not know to what torque to tighten the cylinder-head bolts, but I have a B&S workshop manual and could probably extrapolate from that.
However it is freezing cold in the garage down here, (so much for 'global warming', dream on!!), so I would prefer to try to get it running for now, and leave reconditioning it till the summer. It was not noticeably blowing smoke, and it's power seemed adequate.
I will perform your petrol test, and report back. I gather I should not be using aero start as a favoured standby.
it may be relevant that, for a long while, if I left the machine between uses with the petrol tap not turned off, petrol would leak through the carburettor into the cylinder, and if this were over several weeks, the engine could not be turned over without removing the plug.

The Briggs torque values for head bolts would be fine provided the bolts are the same diameter.

Do not use starting sprays on any engine unless there is a major emergency and ruining the engine is less important than the consequences of not starting it. A poorly tuned fire pump in a bushfire situation is an example.

If you left the petrol on, a large amount of petrol will have ended up in the lubricating oil in the sump. The oil must be changed before starting the engine again, if this has happened.

The purpose of the petrol-in-the-cylinder trick is to see if the engine will run when it has fuel. The normal sequence is to verify that it has spark, compression, and fuel. If you are sure about the spark (i.e. the normal spark plug sparks, not just the one that you gapped to 0.060"), you have now tested the compression (it should start on 50 psi, though it wouldn't thrive), and then you put fuel actually in the cylinder, it should fire unless the valve or spark timing is wrong. The wrong valve timing usually results in flames coming out of the carburetor or muffler rather than simple silence, so we are down to the ignition timing. The only way the ignition timing can get to be wrong on that engine is if the flywheel key has sheared, usually due to mowing a water pipe or stump. So, that is the sequence of checks to make for the moment. If we get to where it is running in a rather gutless and snuffly fashion, it would be time to attend to the valves, which obviously have problems given the strange tappet clearance of the exhaust valve, and the poor compression pressure even when you put oil in the plug hole.

Eureka Grumpy, when I reassembled it the motor started and ran without my having put petrol in the cylinder. This was with a new plug gapped to .025". I think I must have had a plug problem which I did not recognise at the start; or it could just have been the fact that everything got a good cleaning. I will attack the valves and rings in the summer. I am very grateful to you for your constant attention to my queries, and the accurate advice. The Outdoor King forum is one of the best things on the Internet. MacCullum

That makes sense, it sounds as if your plug had caked itself up with some more or less conductive crud over the years. It also explains why you got poor results holding it against the engine, but good ones with a decent plug even though that one was gapped to 0.060" instead of 0.025". A ring and valve job in spring-time will probably make it behave like a new engine. If it doesn't, adding in a carburetor clean is just about sure to.

Thank you for posting the answer to the problem MacCullum - that makes this a useful archive. I'll now close the thread: if anyone needs to add to it, just send a PM to a moderator.