Cold Piston Slap Maybe
Thread Starter
Instructor
Joined: Dec 2005
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From: Burlington WI
Cold Piston Slap Maybe
I posted a few weeks ago about a possible piston slap I hear on my goodwrench crate engine with about 5,ooo miles on it. You only hear
it on cold start for a couple of minutes and a little louder when you put
it in gear. (automatic). Anywhy, I check it out under the hood the other day and it coming from the 3th cylinder on passanger side. If you
increase the rpm's about 200 more it goes away. Now I am wondering
if it not coming from the exhaust heat riser valve slapping back at forth
and when you increase rpm's you increase exhaust flow opening the flapper.
it on cold start for a couple of minutes and a little louder when you put
it in gear. (automatic). Anywhy, I check it out under the hood the other day and it coming from the 3th cylinder on passanger side. If you
increase the rpm's about 200 more it goes away. Now I am wondering
if it not coming from the exhaust heat riser valve slapping back at forth
and when you increase rpm's you increase exhaust flow opening the flapper.
Thread Starter
Instructor
Joined: Dec 2005
Posts: 196
Likes: 0
From: Burlington WI
Not sure if you can tie the flapper open. Mine is operated by vac. and if its working right it should be closed when the engine is cold. The vac. is controlled by VTS mounted in the intake manafold. Now I don't know if it closes on vac or opens but I guessing it opens. Anywhy does the
flapper have holes in it to let the exhaust out when it closed or does have some sort
of spring load to open more when the exhaust flow is more.
flapper have holes in it to let the exhaust out when it closed or does have some sort
of spring load to open more when the exhaust flow is more.
Thread Starter
Instructor
Joined: Dec 2005
Posts: 196
Likes: 0
From: Burlington WI
Ok , I check my heater riser just now and the engine had not been started today, and it has vac. when engine is cold. I unplugged the vac. line and the knock went away. When I put the line back on it came back so its postive that its the heat flapper that is making the noise that sounds like a piston slap. Lucked Out this time.
