Engine damage

[bernard callahan]

I can help you out with engine parts if you need

[Adam]

Cheers Bernard, put offer in on your pistons on eBay, I guess you wanted more, all good, Dale is sourcing for me. How much gear do you have???

[AustHaflinger]

My engine has not run right since my last service - it runs very rich and carbons the plugs in a short time and will not run until the plugs are cleaned.

To fix this I have decided to start over all again with the first step resetting the tappets ten a rebuild of the carb and ignition.

Today I took the rockers off and removed the spark plugs.

With Adam's problem in mind - I manually turned the engine over in reverse for over 50 revolutions all worked as it should - nothing locked, no tight spots and all turned over as it should - visually the tappets and valves were all Ok.

So while the issue you experienced did happen with the engine going in reverse, I suspect it would have also happened if going in the correct direction - so the mystery still remains why? If the pushrod failed first the piston would not have hit the valve so the piston hitting the valve then bending it and pushing the valve up - the valve gear and then bending the push rod.

So was the valve spring and the collets still in place? If they were loose, then the valve could hit the piston but as the valve is on the bottom of the engine it would naturally fall to the closed position and if it was still open free of the spring and collets the piston may very well just push it out of the way with no or minimal damage. Plus you have not mentioned this so I assume the spring was still connected to the valve.

This leads me (Inspector Clouseau) to my conclusion - the rocker pushed the valve down as it should but something then stopped the valve from going back up to the head - this can only be caused by one of four things, valve gear stopping it going up (not likely), something in the combustion chamber stopping the valve going up - this can only be a fragment from a broken valve and there is no evidence of a bit of the valve breaking off - so number three, a sticky valve where the tappet could push the valve down but it will not go back and lastly - in the pic of the valve why is the valve spring broken? If it broke then the valve cannot go all the way backup .

So - My guess is 3 or 4 - so on the rebuild make sure the new valve guides are correct for the valves (on even the areas not damaged) and I would be replacing all valve springs.

Garry

[Adam]

Ah, the plot thickens!!! Garry, after you rebuild your engine could you try doing the exact same thing I did, ie get motor running in reverse through the dyna starter, listen to hear for any bangs and loud noises, if you do hear them, just rev the engine harder, and see if your engine goes bang too!
Then we will conclusively know that running the engine backwards does or does not cause major damage??
Just an idea!!
Before I blew it up I didn’t even know what a valve guide was so all getting a bit complicated. I have ordered all new valves but didn’t order new springs, if you strongly recommend I will get them sent over with the pistons when they arrive.

[AustHaflinger]

I have ordered all new valves but didn’t order new springs, if you strongly recommend I will get them sent over with the pistons when they arrive.

Do I detect a tone of cynicism in your response re starting the engine backward

Well the spring in your pic is broken - see at the end of the arrow in this pic. Zoom in and you can see where it is broken - the broken end should be in your engine somewhere.

So you need new valve springs.

garry

[bernard callahan]

I pretty sure I have new cylinder heads, new valves, new valve stems, complete engine and gearbox gasket sets, and much more, I have a pallet of parts arriving from Austria, it is at Melbourne going through customs, so if all goes well I should have it this week, let me know what you need.

[Adam]

Just waiting on 80.5mm pistons and rings, I think I have everything else sorted!!

[Adam]

Just seems too coincidental that engine was running fine before running backwards that it wasn’t the cause of the dramas!

[heinkeljb]

My engine was running fine and I had done about 25 ~ 30 thousand miles on it and then one journey it decided to snap the crankshaft - It running fine is not a definitive indicator that it will not have issues!

Unfortunately, is is the best indicator that we will be able to use the vehicle the next time we want to!

Glad you have things sorted to the point you will be able to put it back together and have it running again in a short while!

Don’t for get to do a bit of running in before you hammer it!

John

[Adam]

Got all parts now apart from pistons! The new exhaust valve guide I got needs machining as valve doesn’t fit through, is this normal??? Head needs some machining anyway to refit new valve guide anyway so not a problem but would have thought guide would come already sized for valve!

[heinkeljb]

Valve guides can be over size all over. Internal hole can be undersize to allow you to match it to any valve that you can actually get. Outside can be over size to allow you to machine and fit to a damaged hole that has had to be machine to make it correct again. So yes, if you asked for over size valve guides then they should require machining.

John

[Adam]

Cheers John, all good then!!!

[Adam]

Have reassembled bottom end and tightened flywheel and pulley nuts and found 1mm of play in the crankshaft inside casing!! I didn’t disassemble crank, just removed and cleaned everything out! I assume this play isn’t right?? Only thing I can think is main bearing at fly wheel end is around the wrong way??? Does anyone know if the lip on bearing is same both sides or slightly different?? That is the only thing I may have got around the wrong way?? I think!!!!

[Adam]

Read in workshop manual end float of camshaft should be .2mm, and be adjusted by shims!! Would you shim on the inside of the flywheel end main bearing or am I getting ahead of myself???

[Goatwerks]

Just so you understand how it works, engine Oil pumps do not work in reverse rotation, that was the failure.
Top end has most friction, needs lots of oil, first to fail when starved.
Now get that thing back on the road!

[heinkeljb]

I don’t believe the engine actually “ran” backwards for very long so unlikely spring broke due to lack of lubrication. It is obviously possible that lack of lubrication could have caused the valve to stick in the valve guide which then caused the spring to break and bend the push rod. Although, without going back and reading the first post again, I thought it all happened very suddenly with the engine only just running backwards - i.e. not running under petrol power backwards for several seconds.

Correct me if I am wrong!

John

[Adam]

Motor did run for maybe 20 seconds and seemed to be under petrol power, I was stupidly trying to keep running by manually throttling at carby!

[AustHaflinger]

A 4 stroke engine can fire backwards but not actually run backwards. It may fire up as the fuel charge is already in the cylinder but cannot run backwards as it blows the fuel mixture out the inlet valve and tries to suck a none existent fuel air mixture in via the exhaust valve.

When turning in reverse the suck, squeeze, bang, blow cycle is still there but because it is going backwards, it sucks in via the exhaust valve, it compresses with both valves closed and ignition fires (but there is air no fuel), then blows the air out the inlet valve - hence as no fuel can get into the engine it will not continue to run except if the was a fuel charge already in the combustion chamber when that might ignite but once cleared no more fuel can get into the engine.

Irrespective of all that there was a failure most likely the exhaust valve not going back up into the head when it was supposed to (either a sticky valve or a broken spring or a combination of both) and the piston hit it.

Adam - have you found that bit of broken spring?? You need to account for its whereabouts and make sure 100% it has not made its way into the crankcase.

cheers

garry

[Adam]

Crankcase was disassembled and all broken parts found! Once I find some pistons I can afford will put it all back together!!!!

[Julian B]

... hence as no fuel can get into the engine it will not continue to run except if the was a fuel charge already in the combustion chamber when that might ignite but once cleared no more fuel can get into the engine.

Whilst an engine can't "run" backwards, presumably it can be "driven" backwards by the starter motor.