Cb750 Oil pressure very high

[NigelWilmshurst]

Hello everybody
Has anybody had this problem before?

Recent full engine rebuild, now she is run in and I am up to full revs, the problem has shown itself.

Rolling chassis Cb750 F1 1976
Engine Cb750 K4 1974
Tickover no problems, when riding the oil tank overflow at the lowest part of the oil tank chucks oil all over the back tyre.
Possibilities
1, F1 oil tank is not suitable for K4 engine?
2, Pressure relief valve on oil pump is not working properly?
3, I'm thrashing her too hard!
4, when I recently rebuilt the engine I had a choice of 5 oil pumps from K & F1 engines, I chose the best condition oil pump that was well within the wear limits of the service manual and replaced all the o rings and the gasket, all the oil pumps looked the same, are there any different types or are they all the same from 1974 - 1976?
5. Oil tank was blast cleaned and powder coated, very hot process, maybe caused a problem within the oil tank?

All help appreciated
Nigel

[Bryanj]

Most likely is too high a level in the tank not a high pressure

[NigelWilmshurst]

Hi Brian

The level is as it should be on the dipstick when cold, if the oil is not topped up it continues to drop lower on the dipstick, no smoke from the exhaust and the plug colour is good, either the oil is restricted on the return to the pump or pressure is very high, the oil light does not come on as I make sure the oil doesn't run to low.

[mick]

Hi Neil your supposed to check the oil level whilst the engine is hot , ideally after a run  cheers Mick.

[NigelWilmshurst]

Hi Mick

The oil level is below the upper mark on the dipstick after a run, just come back from a spin out to test, tested before and after, the oil level is correct.
I'm sure there is a problem elsewhere

[jimv50]

It could be that the oil is being frothed up when the engine is running, possibly due to the breather not working correctly, can you check this is clear and working as it should be?
Relief valve could well be the culprit though.

[jimv50]

Just had a quick look elsewhere online for similar problems, can you change the oil tank for another one and try it all again?
blocked return pipework was another possibility or another idea was an air oil separator not working as it should.
All a mystery to me all these things,

[NigelWilmshurst]

Thanks all
I will swap the oil tank and check the lines etc, report back ASAP.

[Trigger]

Are you sure that the oil is coming from the oil tank over flow and not the top end engine breather pipe ?

[NigelWilmshurst]

Trig
Definitely the oil tank overflow,
I found on google somebody had the same problem, changed the oil tank and all ok!