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Discussion Starter · #1 ·
95 indy 500. I had a slight coolant leak ever since I rebuilt my top end right around the clutch side base gasket. If that gasket blew could it cause compression loss on that side???? I have a poker run sunday and need a quick fix!
 

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Yes. If that gasket blows, you can suck in air or water, either will eff up your engine and make for an expensive repair.
 

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yes and no, lets say you have a gasket leaking on the side where there is no water, you can say yes you will lose some compression becuase air can leak out as the piston comes down, but in all reality, you have 250 cc of piston coming down at roughly 1000-4000 feet per second depending on rpm, fluid dynamics say that the air is going to go to the least resistance. you have atmospheric pressure on the outside of your engine, when the exhaust port opening and the piston going down you have a vacumme in the chamber, according to physics the amount of air leaking out will be very small, so small that i have a hard time seeing a drop in running compression, BUT with no exuast heat you have no vacumme out the exhaust only from piston drop creating a low pressure in the cylinder, is a small hair line leak enough to change compression? still think you would need a pretty good chunk of gasket missing to show up on a compression guage.


that is also why a tiny leak in the crank seal or base gasket can make a sled run very rich very quickly, that same atmosphere pressure on the outside and vacumme inside the engine make the air want to get into the cylinder.

chances are if you are low on compression there is a tired cylinder from high miles or damage to the piston, rings or cylinder from lean burn or dirt.
 

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id aslo say that a coolant leak if slight would not affect compression, but yes youll need it fixed as it can allow air into the cylinder as well as possibly coolant into the cylinder. if a head gasket was leaking itll definately affect compression. is your compression low or you just see a leak?
 

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Discussion Starter · #5 ·
10 psi on clutch side on top end with 300miles on it
 

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madcow said:
yes and no, lets say you have a gasket leaking on the side where there is no water, you can say yes you will lose some compression becuase air can leak out as the piston comes down, but in all reality, you have 250 cc of piston coming down at roughly 1000-4000 feet per second depending on rpm, fluid dynamics say that the air is going to go to the least resistance. you have atmospheric pressure on the outside of your engine, when the exhaust port opening and the piston going down you have a vacumme in the chamber, according to physics the amount of air leaking out will be very small, so small that i have a hard time seeing a drop in running compression, BUT with no exuast heat you have no vacumme out the exhaust only from piston drop creating a low pressure in the cylinder, is a small hair line leak enough to change compression? still think you would need a pretty good chunk of gasket missing to show up on a compression guage.


that is also why a tiny leak in the crank seal or base gasket can make a sled run very rich very quickly, that same atmosphere pressure on the outside and vacumme inside the engine make the air want to get into the cylinder.

chances are if you are low on compression there is a tired cylinder from high miles or damage to the piston, rings or cylinder from lean burn or dirt.
uhh? ya what he said!^^^ lol no sounds bought right..


heinzsnowmobiler said:
10 psi on clutch side on top end with 300miles on it
10 psi!? yea you deff have a major major problem, bad gasket or something.. start tearing into it... im surprised it would even start.
 

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whoa! major problem there definately not a gasket failure, geez 10 psi? did you put rings in???? thats a joke. but theres a major problem.
 

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madcow said:
yes and no, lets say you have a gasket leaking on the side where there is no water, you can say yes you will lose some compression becuase air can leak out as the piston comes down, but in all reality, you have 250 cc of piston coming down at roughly 1000-4000 feet per second depending on rpm, fluid dynamics say that the air is going to go to the least resistance. you have atmospheric pressure on the outside of your engine, when the exhaust port opening and the piston going down you have a vacumme in the chamber, according to physics the amount of air leaking out will be very small, so small that i have a hard time seeing a drop in running compression, BUT with no exuast heat you have no vacumme out the exhaust only from piston drop creating a low pressure in the cylinder, is a small hair line leak enough to change compression? still think you would need a pretty good chunk of gasket missing to show up on a compression guage.


that is also why a tiny leak in the crank seal or base gasket can make a sled run very rich very quickly, that same atmosphere pressure on the outside and vacumme inside the engine make the air want to get into the cylinder.

chances are if you are low on compression there is a tired cylinder from high miles or damage to the piston, rings or cylinder from lean burn or dirt.
That made my head hurt... Excellent answer though.
 

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Discussion Starter · #9 ·
I replaced pistons, rings, wrist pin bearing, gaskets, plugs and plug caps and checked the head to see if it was warped. Also replaced needle and seat in both carbs. The sled ran amazing, way better than it ever had since I got it. I had no problems at all when I first started riding and had no sign of failure. Coolant temp stayed good and it just flat out lost compression with no warning signs while ridin down the road. Won't run anymore and there's gasket fragments floating in the coolant tank.
 

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the base gasket has to areas to seal, the water rails and the air chambers. it is a good chance that you had a water leak and it could have scored the cylinder down. doesnt take much water to wreck an engine.

but, usually with a water leak into the cylinder you notice a slight drop in rpms or power as the water is killing some of the flame.

10 psi says there is a good chance that you put rings in upside down or the rings got stuck?
 

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figure anyhting out yet?? im curious
 
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