[Fot] Oil Blow-by Cause? Update.

Wed May 22 09:49:33 MDT 2019

Haven’t figured out the problem yet, but I thought this explanation from Longacre on how a leakdown gauge works might interest you all.

"The leak down gauge is simply a 100 psi gauge that reads backwards from a tire pressure gauge. Basically if you have 100 psi going to your cylinder and it doesn’t leak down at all then it will show you 0 leak down and/or 100 psi if it was a normal pressure gauge. If your regulator is set higher then 100 then the leakdown gauge will go below zero because its showing a higher pressure."

So, one of my gauges is no longer reading correctly, as I’m getting a higher pressure on the cylinder than on the supply, on some cylinders.  Have to swap them out to figure out which, and then I’ll be able to determine how much leakdown there really is.  

More to follow this weekend!

On May 22, 2019, at 7:05 AM, John Styduhar <johnstydo at gmail.com> wrote:

If you have an accusump, check if the valve is operating properly.  Maybe the valve was closed accidentally during running and the engine oil level was excessive.  

On Wed, May 22, 2019 at 6:54 AM Robert Lang via Fot <fot at autox.team.net <mailto:fot at autox.team.net>> wrote:
Hi,

First off - I'd only to the leakdown test with the engine hot. Cold numbers don't really count. The numbers that you give look pretty good from a leakdown perspective. As a point of reference, with >10% leakdown into the sump in a couple of cylinders, you will see oil drip out of the strangest places (like around the nuts holding the valve cover down and the filler cap to which you refer.) So, either your gauge is lying or you need to verify your numbers with the engine at operating temps (and see if the numbers change). If you have access to another gauge, that might help figure out if anything is wrong. Oh, and is there any oil fouling on the plugs? Blow by should also introduce some oil into the cylinders when you lift off...

I think Marcel's suggestion has merit.

Let us know if you find anything.

Regards,
Bob Lang

On Wednesday, May 22, 2019, 4:14:19 AM EDT, van.mulders.marcel--- via Fot <fot at autox.team.net <mailto:fot at autox.team.net>> wrote:

If the catch can has a connection to a (low) spot of the crankcase, lots of oil can be pushed into the catch can at the track curves, especially when the duct between the crankcase and the can has only a small diameter, then the oil cannot return to the crankcase. It means there is some blow by, but maybe the symptoms are not necessarily bad  news.
Marcel

Van: "fot" <fot at autox.team.net <mailto:fot at autox.team.net>>
Aan: "fot" <fot at autox.team.net <mailto:fot at autox.team.net>>
Verzonden: Woensdag 22 mei 2019 04:31:47
Onderwerp: [Fot] Oil Blow-by Cause?

I just had a great weekend at Summit Point, perfect weather, four days and lots of track time, some quick laps and good racing.  
After my last session, I noticed some dripping oil as I put the car in the trailer.
Got it home to find a half full catch can (1 pint?), and evidence of oil blowing out of the valve cover cap vent hole.
Tonight I ran a compression test and leakdown test.  Cold engine results:

1 - 200 and 2%
2- 180 and 6%
3 - 180 and 9%
4 - 195 and 0%
5 - 190 and 0%
6 - 185 and 0%

Note - I suspect my longacre leakdown gauge may not be reading quite right, as when i have the air side set to 100, the leakdown % on the last three is slightly below zero.  So, perhaps the leakdown on the first three is higher. 
There was no excess oil until the last session.  Oil pressure is about 50 hot at idle and 65 - 75 at speed, depending on RPM.
EGT readings remained in the 1200 - 1250 range across three monitored cylinders at top speed
What do i have - failing rings?  
Any diagnosis or tests you recommend before I start pulling the thing apart would be appreciated.

Triumphs racing - I’m sure I’m missing a few but this is who I remember.
TR3 - John Hasty, Henry Frye, John Styduhar
GT6 - me, Paul King, Jason Sukey, Jay De Pol until his diff case broke
Spitfire - Russ Moore, Marty Sukey, Jeff Govert, Kent Bain, others 
Tr4 - Mark Wheatley, Allen Goode, I’m missing at least another one

Scott Janzen

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