r107 450SL engine getting tight when up to temp

[RaceDiagnostics]

Initially I thought I had an alternator battery issue as the battery seemed flat when trying to start the engine while hot, but when replaced with a brand new 92Ah battery the results are only marginally better. The engine cranks very slowly as if the battery is almost flat, but does eventually fire up.

This only happens when hot, it spins up quickly when cold.

I had planned to check the force needed to crank the engine with a toque wrench tonight at both hot and cold but unfortunately there is no way to attach the troque wrench to the crank shaft as the fan is in the way.

Any suggestion on what could be causing this tightness, this may also be the reason that it ticks over so slowly when hot.

 

[BlackC55]

Take the fan off and crank by hand when hot to be sure.

 

[BlackC55]

Or take the belts off completely to see if you have a seized pulley somewhere. You can start the engine with the belts off briefly.

 

[219]

Is the starter motor definitely OK ? Not losing grounding with temp increase ?

Although the slower hot idle seems to point away from this and something may be seizing , it could just be due to cold start enrichment cutting out ?

 

[Bellow]

Over advanced ignition timing?

 

[RaceDiagnostics]

One month on and the tightness has gone, ther is still a diffrence between cold (instantaneous) and hot (one to two seconds of cranking), but the tight, slow hot cranking has gone.

I guess it was something to do with sitting in a garage undriven for a year.

 

[RaceDiagnostics]

When I get a chance after checking out my compression issue I will report back on the cranking torque at hot and cold.

 

[stwat]

I had this problem on a VW T25 Transporter. It would get so bad that the starter simply wouldn't turn over when hot.

It turned out to be corroded earth wire from the starter motor. Once i cleaned up the connections the problem was cured.