More Power
07-07-2004, 15:31
I received the following email, and I thought the info might be useful here in the BB.
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Greetings, I was wondering if you could tell me what the proper valve spring specs are for the 1997 6.5 engine. I believe, Intake and exhaust are the same. Just need the Lbs at given height. Also, what is the correct cylinder pressure in P.S.I. I've got #4 intake leaking up thru the intake manifold when pressurized. I removed the spring and it checked at 240lbs at 1.4 inches and that's what my local machine shop said was within spec's but they didn't seem to knowledgeable on the 6.5 engine. As I rotate the valve against the seat with the valve spring removed, it feels like there's a build-up of carbon on the seat, it has the feeling that it is "ramped up " . All cylinder's compression check at 440 to 460 lbs, except #4, it's got 380 lbs. Any suggestions? Thanks Kevin
Hi Kevin,
There isn't a free length spec, but installed height should be 1.1811", and there should be 80-lbs of pressure at the installed height for both intake and exhaust.
I recommend replacing all valve springs whenever the engine or cylinder heads are rebuilt. We hear about broken valve springs once or twice a year, which can lead to more serious engine problems. New springs are relatively cheap.
Cylinder pressure can vary quite a bit between engines, but the GM specs are 250 psi minimum with the lowest measured cylinder being no lower than 80% of the highest reading cylinder. Generally, a healthy 6.5 will produce 350+ psi of cylinder pressure when measured after 4-6 puffs with a warm engine. Higher cranking speeds produce higher pressures, as does spinning the engine for more than 6-8 puffs. This explains the variability.
Good luck,
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Greetings, I was wondering if you could tell me what the proper valve spring specs are for the 1997 6.5 engine. I believe, Intake and exhaust are the same. Just need the Lbs at given height. Also, what is the correct cylinder pressure in P.S.I. I've got #4 intake leaking up thru the intake manifold when pressurized. I removed the spring and it checked at 240lbs at 1.4 inches and that's what my local machine shop said was within spec's but they didn't seem to knowledgeable on the 6.5 engine. As I rotate the valve against the seat with the valve spring removed, it feels like there's a build-up of carbon on the seat, it has the feeling that it is "ramped up " . All cylinder's compression check at 440 to 460 lbs, except #4, it's got 380 lbs. Any suggestions? Thanks Kevin
Hi Kevin,
There isn't a free length spec, but installed height should be 1.1811", and there should be 80-lbs of pressure at the installed height for both intake and exhaust.
I recommend replacing all valve springs whenever the engine or cylinder heads are rebuilt. We hear about broken valve springs once or twice a year, which can lead to more serious engine problems. New springs are relatively cheap.
Cylinder pressure can vary quite a bit between engines, but the GM specs are 250 psi minimum with the lowest measured cylinder being no lower than 80% of the highest reading cylinder. Generally, a healthy 6.5 will produce 350+ psi of cylinder pressure when measured after 4-6 puffs with a warm engine. Higher cranking speeds produce higher pressures, as does spinning the engine for more than 6-8 puffs. This explains the variability.
Good luck,