Rev high, lose compression, no bent pushrods???
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From: Calgary Alberta
Rev high, lose compression, no bent pushrods??? Ok I've had a miss on #5 ever since I missed a shift and rev'd up too high.
I had bent pushrods, replaced them, but still had a miss.
I did a compression text on #5 and it had compression, was in the "green" part of my compresson gauge. But this weekend, I took the time to check the compression of the other cylinders, and #5, although it has compression, has considerably less then the surrounding cylinders. This would explain the missfire...
How can over reving the engine cause a misfire, I'm thinking a bent valve?
Ideas? Heads are coming off tonight, what should I look for?
I had bent pushrods, replaced them, but still had a miss.
I did a compression text on #5 and it had compression, was in the "green" part of my compresson gauge. But this weekend, I took the time to check the compression of the other cylinders, and #5, although it has compression, has considerably less then the surrounding cylinders. This would explain the missfire...
How can over reving the engine cause a misfire, I'm thinking a bent valve?
Ideas? Heads are coming off tonight, what should I look for?
Thread Starter
TECH Enthusiast
Joined: Jul 2007
Posts: 622
Likes: 2
From: Calgary Alberta
How do I make this fitting?
Thread Starter
TECH Enthusiast
Joined: Jul 2007
Posts: 622
Likes: 2
From: Calgary Alberta
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Your indication is low compression as opposed to no compression. Likely an eyebrow in the piston but it doesn't sound like short block issues from your description.
Last edited by vettenuts; Aug 18, 2009 at 04:14 AM.
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I had a simillar problem on my car...started as a miss only at WOT that would come and go...then became a miss all at any rpm in any driving condition that would come and go....and now it has become a completely dead cylinder all the time...#7 seems to be the one that is affected on my car....any input guys? and btw I'm sorry for hi-jacking...
-Dave
-Dave
The fact that your pushrods were bent is a giveaway that there was piston-valve contact. The valve could be bent just a hair and not quite seating properly, giving you lower compression readings. The only way to know for sure is to do a leak down as mentioned earlier or pull the heads (which you are doing anyway). I would be suprised if it was in the lower end.
I had a simillar problem on my car...started as a miss only at WOT that would come and go...then became a miss all at any rpm in any driving condition that would come and go....and now it has become a completely dead cylinder all the time...#7 seems to be the one that is affected on my car....any input guys? and btw I'm sorry for hi-jacking...
-Dave
-Dave
The fact that your pushrods were bent is a giveaway that there was piston-valve contact. The valve could be bent just a hair and not quite seating properly, giving you lower compression readings. The only way to know for sure is to do a leak down as mentioned earlier or pull the heads (which you are doing anyway). I would be suprised if it was in the lower end.
I've replaced the plugs, wires, injectors, coil packs...everything possible on the outside of the motor....
Thread Starter
TECH Enthusiast
Joined: Jul 2007
Posts: 622
Likes: 2
From: Calgary Alberta
exactly. look for a bent valve, should not be bottom end related. best way to notice a bent valve is to look at the outer edge of the valve versus the valve seat, look at is as two circles one inside the other, the bent valve will lean toward the edge of the seat. there should be even space all the way around the outer diameter of the valve head to the valve seat outer circle.
I got almost all the bolts off, just have the little ones under the intake, and the one under the valve covers closest to the firewall to get out.
So hopefully I will know tonight.
I guess I never thought about it, but a bent pushrod would have to indicate piston/valve contact....
Hopefully I'll pick up some ponies with the 243's as well.
You guys rock...
I got almost all the bolts off, just have the little ones under the intake, and the one under the valve covers closest to the firewall to get out.
So hopefully I will know tonight.
I guess I never thought about it, but a bent pushrod would have to indicate piston/valve contact....
Hopefully I'll pick up some ponies with the 243's as well.
I got almost all the bolts off, just have the little ones under the intake, and the one under the valve covers closest to the firewall to get out.
So hopefully I will know tonight.
I guess I never thought about it, but a bent pushrod would have to indicate piston/valve contact....
Hopefully I'll pick up some ponies with the 243's as well.
