Sq4 MkI - what now?!?

[Gui.dorey]

The picture looks idilic, but it’s not. My Sq4 broke down on my first ride this year.

Everything was going smoothly and after 45km I was on my way back home, riding at about 80km/h when suddenly a metallic noise came up and a second later there was a sort of bang and the engine seized. I grabbed the clutch and rolled to a stop. Some nice blokes in the village nearby loaded her on to a trailer and drove me home.

It sounded like a chain had broken, but checking both primary and rear all is normal. The gearbox is also working normally and she rolls in neutral, but the engine just doesn’t turn. Checked the rocker boxes and all seems normal in there. Took off the timing cover and the chain is intact and no other signs of any damage. I then tried turning the engine back and forth with a socket on the rear crankshaft nut. It does move a few degrees, but there is a sound like loose metal parts inside the cases and one can’t turn it further in any direction.

Tomorrow I’ll take the sump off and try to see if I can spot anything from underneath, but I have the awful feeling I shall have to open the engine up again. And this when all my previous troubles with wet sumping and blown head gaskets seemed to have been solved.

If I have to open her up again, I think I’ll just park her into the darkest corner of the shed and leave the Sq4 for a long time and just enjoy my other bikes.

[Paul_Linden]

That’s a sad story, Gui, and one that a square four owner never wants to experience.

[paul.jameson]

I am truly sorry to hear that Gui after you had done so much work and were making such good progress with the bike. It does appear that opening the engine up again will be necessary but you might be lucky when you take the sump plate off. Clearances in the Square Four bottom end are very small so something like an errant nut could be the problem.

[Gui.dorey]

Well, it was the no. 3 rod that failed…
Why? I don’t know. Sludge traps were meticulously clean, everything built up as it should, but somewhere something was wrong, I missed something or made a mistake somewhere.

I suspect something to do with the lubrication system. Those who followed my tribulations know I had a problem with wet sumping and I put it down to the morgo which was letting oil flow through. I had the pump repaired at Morgo and thought that was it, but now as I opened up the sump the cases were again full of oil as you can see in the picture. So I suppose for some reason the pump is pushing the oil into the cases or not scavenging (although I could always see a good flow of oil back into the tank), and the oil is not going where it should be.

The 2nd pic one can see some of the bits that fell out of the sump. Rod and piston are destroyed and probably also the piston liner and God Knows what else. From what I could see from underneath the other 3 rods are intact, but who knows what collateral damage they have suffered.

The Sq4 has now been relegated to the back of the shed under a sheet until I get the courage to pull out the engine. What I’ll do with it, I still haven’t decided. Brake it up for parts, sell it as it is, try to find a good replacement engine…. I just don’t want to think about it at the moment.

Cheers
Gui

[Paul_Linden]

In the lower picture it looks like I can see both bolts that hold the number 3 big end together. They are both very damaged, but one looks like it may have come loose?
Also, this looks like an original rod and big end bolts, not the new club rods and bolts. If that is the case then that might be a clue as to what happened.
Apologies if I’m reading too much into the second photo, and they are club rods.

[JohnnyBeckett]

if you like to run a sq4 you will need deep pockets to kee[ it running , i stop running my ones years ago except one that has got a old harley side valve engine fitted by dad over 30 years ago because he said the sq4s were unreliable ,so my ones are in the back of the barn

[simon.holyfield]

That’s a sad story, Gui, and one that a square four owner never wants to experience.

It is indeed. Our thoughts are with you Gui - can I assume that at least the cases are OK?

Another question - how did you retain the sludge trap plugs? One of my worries is one of them coming loose.

I'm thinking about taking mine off the road until I have changed the rods. This feels like a warning for me too.

[paul.jameson]

Definitely an original rod rather than a Club one. We know the head and barrel had been skimmed many times so it may well be that this is a relatively high mileage bike - or a high load sidecar bike - where the rod had reached the end of its fatigue life. When a rod fails due to the big end seizing because of lack of lubrication the end of the rod left on the crank usually punches its way out through the casings. Only a stripdown will indicate what happened.

I can't say that I would criticise you for throwing the bike in the back of the shed and leaving it there but I do hope that you decide to undertake the repairs.

[nevhunter]

I don't blame you for wanting to push it out if sight and mind. Might just have been a "tired" rod. Unless you know the bikes history the only way to avoid this is to put a new set of rods in. Alloy rods are known for having a defined life. Speedway JAP rods were replaced each season and still failed if you geared the bike too low for the track. Nev

[allan.walker]

That's rotten luck, Gui and I sympathise with you.

I recently finished the rebuild of my Square Four. I bought it as 'rebuilt' and I had ridden it for about 1000 miles, but it developed a knock so I stripped it down. Number 4 big end journal was very worn, so I thought that I had found the source of the knock. On investigation, I found that the number 4 conrod big end eye measured 5 thou small and it had 'pinched' the ends of the shells together. This created two tight spots which, I assume, acted as 'wipers' across the surface of the journal and removed the oil film.
(All the rods were original factory ones, btw.)
All the other journals and shells were good. The crankshaft oilways were clean as a whistle, as were all the oil galleries elsewhere, so the P.O. did some things correctly.

I rebuilt the engine with a reground front crank from my spares box, new Club rods, big ends and mains (and lots more) and I sent the Morgo oil pump back to Morgo for a precautionary service.
Having rebuilt it, I started it and ran it at a fast tickover for a few minutes. There were no untoward noises and the oil was returning nicely. I stopped the engine and put the bike away. Next day, I re-torqued the head and started the engine again. No problems, running nicely, good oil return.

One mile into a test run and the engine sounded unhappy, with a distinct clatter and knock, so I stopped and checked the oil return. There was no oil returning and the tank was half-empty. I stopped the engine and got the bike home.
Up on the bench (again) and I removed the sump plate, together with the oil which should have been in the tank.
I drained the remains of the oil from the tank and the last dregs came out looking like badly-stirred metallic paint.
(I had removed and thoroughly cleaned-out the oil tank as part of the rebuild.)
I was suspicious of the sump filter, so I put an old filter in from another engine. I refilled the oil tank, re-bled the oil pump, fitted an oil pressure gauge and started the engine. The oil returned properly, the oil pressure was good, but oh dear, did the engine knock!
I let it run for a minute or two and then chickened-out and stopped it.

I've stripped the engine again. The big ends have very slight marks and the shells are scuffed. The journals have worn by 0.7-0.8 thou from what they were when I measured everything before fitting new shells and rods, but are not oval. They look like they should polish-up alright. New shells will be needed, obviously.
Is this the cause of the knocking, I wonder?
The timing-side bushes are lightly scuffed, also.

So, what had happened? The oil return had stopped, hence the emptied tank. Wear to the big ends gives me concern about the oil feed, too.

Anyway, I shall continue with the 2nd rebuild.

I didn't intend to hijack your thread, Gui. I felt sick about having to take the engine apart again, so I can imagine how you feel about it. All I can say is that there are reasons for mechanical failures, so things should be fixable. Just dive-in there and see what you find. When you know what you are facing, you can make a decision on what you want to do.

All the best,
Allan.