Square Four MkI restoration complete - almost....

[simon.holyfield]

If I do remove the timing chain, I’ll lose my valve timing, right? That was another nightmare I wanted to avoid. It took me ages to get it right...

Very true. Try a socket wrench on the dynamo and crankshaft nuts, just to be sure the dynamo is free - you will probably see the camshaft move a little bit too. You might want to slacken the cam chain tension, which will give you more movement.

I would have thought that there was enough clearance in the coupling gears for you to see one of the crankshafts move. I think you will be able to get some indication of where the problem is with the timing and primary covers off.

[Gui.dorey]

I just had a horrible thought. Is it possible that a cylinder sleeve could drop down? That as the engine got warmer there was enough expansion to allow the steel sleeves to move? Is it even possible for something like that to happen?

[Mick D]

Hi

It's possible but highly unlikely - better off removing the covers, finding something that moves, (no matter how little), and working through the trains of adjacent components until you find one that's stuck fast.

If you haven't dropped a valve or displaced a push rod there's little else that can go wrong with the head, (a seized rocker would be unlikely), so it's sounding like bottom end or piston.

Regards Mick

[john.whiting]

A piston seizure will generally free as the engine cools,whereas a bigend seizure will always tighten.........a simple nip up is not serious and a quick clean with abrasive paper and a new shell is all thats needed.

[simon.holyfield]

I just had a horrible thought. Is it possible that a cylinder sleeve could drop down? That as the engine got warmer there was enough expansion to allow the steel sleeves to move? Is it even possible for something like that to happen?

I doubt it. I've measured very high temperatures at the cylinder heads in the region of the plugs, plenty hot enough to loosen a liner but there are two things to bear in mind.

Firstly, that temperature would have to exist all the way down the block to allow the liner to slip - not going to happen. You need the whole block in the oven to get them out.

Secondly, aren't the liners stepped at the top to located them axially?

[roger.fellows]

Gui, I don't understand why you might be able to move the engine with the camshaft nut and not the crank nuts.
The square belonging to my late father had a Huntmaster engine sprocket which meant that when the sprocket was tightened it was sandwiching the coupling gear cover. Two of us spent some time pushing Dad up and down the road trying to get it to run. It did start eventually, and Dad rode it for 1,000 miles or so. The contents of the primary case looked exactly like aluminium primer when I opened it up.

The correct sprocket has a spacer to hold it off the case.

If you photograph the timing side and put it back as a copy it should be right - positions of all keyways recorded and a mark on the chain against a sprocket - and don't move the dynamo shaft. Avoid enough rotation to hit an open valve?????????

[Gui.dorey]

Gui, I don't understand why you might be able to move the engine with the camshaft nut and not the crank nuts.

Hi Roger, misunderstanding there. I meant before when I was assembling the engine. At the moment everything is locked.

I’m getting an engine endoscope from a mate and try to peek in to see if I can see anything inside before starting to disassemble anything. But many thanks for all the suggestions. I’ll start trying them if I can’t find anything with the endoscope.

Cheers
Gu

[roger.fellows]

Yes, that's what I took you to mean - if it turned at all it must surely move for any of them??????

Sorry, probably being dense.

[Gui.dorey]

I'm not sure. I think maybe because everything was still very tight after the rebuild, and somehow it was easier through the camshaft? I mean, it wasn't stuck like now - I could do a few degrees back an forth but not more than a full rotation before I became afraid that something would brake or be damaged. Maybe I was just being too careful. Before it started the first time and ran a few times, I really had to put all my weight into the kick. There was no way to even move it unless the bike was on the stand. On the last run Sunday morning I could already do a half kick while straddling the bike with my left leg on the ground. At least with a warm engine. Everything was noticeably looser. I would expect to be able to turn the engine with a socket wrench on the crank nuts now, if it wasn't stuck. Let's see what the endoscopy will show.

[david.anderson]

With regards to the cylinder liner dropping, that is not uncommon with the 4 and I have seen it twice and heard of others. The 4s run very hot and many cylinders have expanded a little resulting in there being inadequate interference fit for the liner. What then can happen is that as the cylinder gets hot it expands away from the liner to a point where there is no or minimal interference fit. The liner is still retained by the lip at the top. The liner can often develop a crack at the point of the lip and with a piston seizure the piston grabs the liner and breaks it around the top lip and then the liner is pulled down into the rotating crankshaft and broken into hundreds of pieces. For that reason the liners in my 4 are also pinned at the bottom through the cylinder. My alloy cylinder VH developed a crack at the point of the lip, which resulted in immediate replacement and the replacement liner was also pinned at the bottom. However I do not believe that is your problem. it would not happen as an engine cooled.
I would first be looking at your drive train for a problem. Can you spin the back wheel with the gearbox in neutral. If not the problem may be a bush in the sleeve gear has moved in or out locking the gearbox. Then check the primary drive and clutch. And finally Johns suggestion of a seized big end is the most likely.
David