[Fot] Oil Pressure Conundrum

[Peter Vucinic]

Marty,

Sounds like some of the bearings clearances are larger than they should be
and you are losing oil pressure as the oil warms up and starts leaking
through the journal(s) faster once you are at operating temps. 

If you are running an aggressive cam profile and/or high valve spring rates?
This will adversely affect cam bearing wear for sure.

 

 

"You can Make a Small Fortune From Motor Racing. As long as You Started With
A Lage Fortune!"

Kind Regards

Peter Vucinic

TR4 - TR7 V8 - Spitfire MkII

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From: Fot [mailto:fot-bounces at autox.team.net] On Behalf Of marty
Sent: Tuesday, 12 July 2016 4:09 AM
To: FOT
Subject: [Fot] Oil Pressure Conundrum

 

  

I could use some opinions. Some history. Spitfire small journal 1296 engine,
rebuilt 6 race weekends ago included all new bearings. I tore it down this
spring to check it over prior to last weekend PVGP event. Cam and crank end
floats were to spec. Rod and main bearings checked between .002 and .003
clearance. I do not have the actual numbers in front of me at the present.
Cam bearings appeared to have some slight visual wear at the bottoms but I
did not actually measure them. I run Brad Pen 20W50. Oil temps run 210 and
water temps run 190. EGT are 1200/1250 range on track. I was fighting low
oil pressure at running temps all weekend. Once my oil temps come up on
track the pressure drops down to 35psi. If I add enough springs to the
pressure relief valve I see over 125 psi cold so I am thinking my pump is
putting out enough pressure. I tried shimming to get 50/60 cold at idle and
it drops to 35 at operating temps at 7000 rpm. I tried a new pressure gage
over the weekend and the numbers did not change. I am currently running an
auxiliary oil line to the head, I removed it at one point over the weekend
and it had no effect. I tried a new pressure relief valve assy and it had no
effect.  I believe this situation actually started a season ago because I
added a washer to the pressure relief valve last season.  I'm thinking it
most likely is cam bearing wear even though all the bearings were fresh 6
events ago. Any guidance? One thing I did learn this weekend is my accusump
pressure gage is incorrect.  It was reading about 30 psi higher that my dash
gage. I was thinking it was probably correct and my dash gage was wrong
until I replaced my electric dash gage with a mechanical gage and its
reading matched the gage I just disconnected. Oil pressure readings are
taken at the port below the distributer. 

 

Side note. Car ran awesome. I ran a 2.22 at PittRace Sunday and that was 6
seconds faster than my previous best lap there. 

 

Thanks,

Marty 

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