[Fot] Oil Pressure Conundrum

Wed Jul 13 06:12:48 MDT 2016

Marty, I think Peter is right. The GT motor I am about to rebuild had similar symptoms. Great pressure cold, 75-80, then dropping to 20-25 hot at idle, sometimes less and I had to keep RPMs up to ensure lubrication. Uppon teardown, I had a a couple of big end rod bearings showing some copper, and others indicating wear also, all on the compression stroke side (opposite side of oil journal). Mains were all OK. I run street Mobil One 15-50, but think I will change after rebuild.
Would welcome a few race oil opinions from FOT
BestBrian

26A GT6+, 28 TR6Brian Schirano
585-305-0349 Cell 
BSchirano at yahoo.com

      From: Peter Vucinic <pvucinic at netspace.net.au>
 To: 'marty' <trmarty at hotmail.com>; 'FOT' <fot at autox.team.net> 
 Sent: Tuesday, July 12, 2016 9:54 AM
 Subject: Re: [Fot] Oil Pressure Conundrum

#yiv0474239424 #yiv0474239424 -- _filtered #yiv0474239424 {panose-1:2 4 5 3 5 4 6 3 2 4;} _filtered #yiv0474239424 {font-family:Calibri;panose-1:2 15 5 2 2 2 4 3 2 4;} _filtered #yiv0474239424 {font-family:Tahoma;panose-1:2 11 6 4 3 5 4 4 2 4;} _filtered #yiv0474239424 {font-family:Consolas;panose-1:2 11 6 9 2 2 4 3 2 4;}#yiv0474239424 #yiv0474239424 p.yiv0474239424MsoNormal, #yiv0474239424 li.yiv0474239424MsoNormal, #yiv0474239424 div.yiv0474239424MsoNormal {margin:0cm;margin-bottom:.0001pt;font-size:12.0pt;}#yiv0474239424 a:link, #yiv0474239424 span.yiv0474239424MsoHyperlink {color:blue;text-decoration:underline;}#yiv0474239424 a:visited, #yiv0474239424 span.yiv0474239424MsoHyperlinkFollowed {color:purple;text-decoration:underline;}#yiv0474239424 p {margin-right:0cm;margin-left:0cm;font-size:12.0pt;}#yiv0474239424 span.yiv0474239424EmailStyle18 {color:#1F497D;}#yiv0474239424 .yiv0474239424MsoChpDefault {font-size:10.0pt;} _filtered #yiv0474239424 {margin:72.0pt 72.0pt 72.0pt 72.0pt;}#yiv0474239424 div.yiv0474239424WordSection1 {}#yiv0474239424 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 RegardsPeter VucinicTR4 - TR7 V8 - Spitfire MkII_______________________________________________fot at autox.team.net  http://www.fot-racing.com  Donate: http://www.team.net/donate.htmlArchive: http://www.team.net/archiveForums: http://www.team.net/forums        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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