78 750 engine tightens up at temperature.

[Bluelrush80]

Hello, I have had this bike since 06 it ran great until 2010. This is when it began cranking slow. I had thought the starter was getting weak (I put a new battery in it). It would still kick start just fine. Then the front brake caliper started locking up and I was having difficulty finding parts so it sat. In 2023 I sent my bike to my a friend who has done a lot more motor work than myself. He has gotten it freed up so that the starter will crank and start it, but it still gets tight as it warms up. He went through the top end, changed oil again, ect. Any suggestions when to look?

 

[Signal]

I suspect the the bike is fine mechanically,
What do you mean by gets tight ?
Describe what happens when you press the starter button.
Compare kicking the bike over cold and hot . If it is the same then the problem is most likely in the electric starter system.

If so check the easy stuff first , are the starter motor connections clean and tight with cables in good condition.
How old is the battery although a dud battery would probably struggle more with a cold motor.

 

[Max Midnight]

Are you talking about the brake or motor tightening up?

If the latter how does this manifest itself?

 

[Bluelrush80]

Sorry, everyone I mean the engine. My cousin was working on it when I sent it to him the engine was hard to roll over manually. He got it freed up and could start it with the electric start. He rode it about a mile. When he pulled the clutch in the motor died. He says when the motor comes up to temperature it is trying to seize up.

 

[Max Midnight]

Whilst it is possible to offer theories they will be no more than that.
They may hit the nail on the head but can also send you i the wrong direction.
The only way you will get an accurate diagnosis is by inspecting each element of the system.

You say it cuts out when the clutch is pulled in but what happens if it was ridden for a longer distance without the need to stop?
If it runs OK then I would look towards a fuelling issue at low revs or idle.

If the engine is getting tight then the most likely cause would be lack of lubrication so you need to ensure that the pump is functioning as intended.
Ensure that filters aren't blocked that the pump has drive.

That said it is unusual for a four stroke to tighten up as you describe as you haven't done anything to the bores/ pistons or rings.

 

[Its been a long time]

750 triple? Seems possible the oil pump has lost it's drive?

 

[Signal]

I am at a loss as to your problem .
The oil pump is in the sump and driven off the starter motor system under the LHS engine case.
If it is the oil pump the plain bearings on the crank a probably toast. Crank bearings for the XS triples are getting hard to find . Good news is that XS750/850/1100 bearings are mostly the same, except the 750 has one set with a thrust shoulder on it.

 

[Max Midnight]

Just to clarify so we are on the same page, is this an XS650 bored to 750 or an XS750?