Engine Cant figure this one out

rockyracoon

10 Year Member
Nov 23, 2005
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margate NJ
Don't know why but my motor cannot be rotated when I install the spark plugs. Without the plugs it rotates fine. Could oil have Gotten into the cylinders ? If I put compressed air into a cylinders and rotate the motor that cylinder holds pressure when both valves are closed and releases air into either the intake or exhaust manifold,as it should.
 
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rockyracoon

10 Year Member
Nov 23, 2005
711
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margate NJ
Hypothetical question. If I removed all the rocker arms so that all the valves are closed and then installed the plugs should I be able to rotate the motor by hand ? The only thing I can think of is the push rod length is too short. I measured using an adjustable push rod checker and if memory serves they were 6.75. This is with aluminum heads 1.6 roller rockers and trick flow stage 1 cam.nothing was decked . Number 1 at tdc on comp stroke and timing marks line up. It doesn't seem to be mechanical. It feels like cylinder pressure is keeping the motor from rotating. None of the spark plug electrodes are crushed or anything.any help greatly appreciated.just really strange that motor rotates by hand with the plugs removed but not when plugs are installed.
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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To answer your question, yes if all the valves are closed the compression has no where to go and no way to suck in air, It's difficult when turning the engine over by hand when valves are opening and you only have a couple cylinders with compression.
This is just my thoughts and in no way based on actual mechanical experience.
 

rockyracoon

10 Year Member
Nov 23, 2005
711
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margate NJ
Update
motor will rotate with breaker but it takes a lot of effort. It just seems like compression is bleeding off awfully slow . I'm going to install the flywheel and bell housing and try to rotate the motor with the starter before I stab it back into the car.
 
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rockyracoon

10 Year Member
Nov 23, 2005
711
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margate NJ
General karthief. So that's what I figured.
and I'm starting to wonder about push rod length being off. If they were too short wouldnt the effect be similar to the hypothetical ?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Why do you need to rotate the engine?
the push rods should be long enough to open the valves to allow air in and out even if they are too short. The engine is not going to be easy to rotate by hand anyway. Was the engine recently assembled and the mains and rod bearings checked?
 

rockyracoon

10 Year Member
Nov 23, 2005
711
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margate NJ
So I noticed my lifters are all spongy thus maybe not getting proper valve lift. I took the rod out of an old dizzy to try and get some oil up top using a drill. I did the garden sprayer method but I guess they bled back down as it's been about a month since I did that. Hopefully the drill can get the lifters pumped up.
 
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rockyracoon

10 Year Member
Nov 23, 2005
711
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margate NJ
Rods and main bearings were not changed. Just a CHI swap. That being said I'm going to install the bell and starter while still on the stand to make sure the factory starter has enough grunt to spin the motor.
 

Mustang5L5

This is a big reason why I pulled it out
Mod Dude
Feb 18, 2001
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Going to be awfully hard to rotate an assembled motor by hand with the plugs in. Compression bleeds off VERY slowly through the gaps in the rings, so when you have a cylinder on the compression stroke, you really need to be a he-man with a breaker bar to turn the engine over.

Starter uses mechanical advantage with a large diameter flywheel, and a small pinion gear. That's why they have enough grunt to spin the motor, vs you doing it by hand on the crank.
 
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