09-16-2018, 01:31 PM
Help! This has me baffled.
In the last practice session on Friday at Oreville I thought I heard a slight "tink" coming off the hairpin, then the head temp jumped up over 400 and the the next time off the hairpin the engine bogged a little bit. OK, air leak right?
So Saturday morning I pressure tested the engine (91B-1) and it was tight as a drum, so the leak must be in the carburetor. I replaced the base gasket and trimmed a half inch off the fuel line to get a fresh end and went back out. Now it's running at 370 head temp (my normal max) AND 4 cycling about half way between the kink and the restart box. Then when I pulled into the pit lane it just shut off.
I tried to restart it in the pits and it wouldn't fire. I pulled the plug and it was badly oil fouled. I replaced the plug and it started and ran with the rear wheels off the ground, but as soon as I stepped on the brake it stalled. Changed carburetors and it did the same thing 2 or 3 more times. OK, change engines (that's why I missed qualifying). So now at home, I pressure tested the engine again; tight as a drum.
Oh, by the way, I was also loosing clutch oil at an abnormally high rate. It's the Margay gearbox wet setup where the oil bath is in contact with engine PTO seal. Could it be that the PTO seal is sealing under pressure but leaking under vacuum, thus sucking clutch oil (and air) into the engine? In my demented mind that would account for all the symptoms including the "tink", which could have been the seal spring blowing through the engine without hitting anything important. Or am I grasping at straws?
Anyway, I just wanted to see if anybody could shed some light on this for me before I tear down an otherwise perfectly good engine. Thanks.
Bill.
In the last practice session on Friday at Oreville I thought I heard a slight "tink" coming off the hairpin, then the head temp jumped up over 400 and the the next time off the hairpin the engine bogged a little bit. OK, air leak right?
So Saturday morning I pressure tested the engine (91B-1) and it was tight as a drum, so the leak must be in the carburetor. I replaced the base gasket and trimmed a half inch off the fuel line to get a fresh end and went back out. Now it's running at 370 head temp (my normal max) AND 4 cycling about half way between the kink and the restart box. Then when I pulled into the pit lane it just shut off.
I tried to restart it in the pits and it wouldn't fire. I pulled the plug and it was badly oil fouled. I replaced the plug and it started and ran with the rear wheels off the ground, but as soon as I stepped on the brake it stalled. Changed carburetors and it did the same thing 2 or 3 more times. OK, change engines (that's why I missed qualifying). So now at home, I pressure tested the engine again; tight as a drum.
Oh, by the way, I was also loosing clutch oil at an abnormally high rate. It's the Margay gearbox wet setup where the oil bath is in contact with engine PTO seal. Could it be that the PTO seal is sealing under pressure but leaking under vacuum, thus sucking clutch oil (and air) into the engine? In my demented mind that would account for all the symptoms including the "tink", which could have been the seal spring blowing through the engine without hitting anything important. Or am I grasping at straws?
Anyway, I just wanted to see if anybody could shed some light on this for me before I tear down an otherwise perfectly good engine. Thanks.
Bill.