Engine Low compression in all 8 cylinders

[zlightlystoopid]

Whats up guys after my gt40 heads, upper and lower intake and tfs1 cam swap the car runs good but idles rough and seems to be misfiring so i checked the compression today and all 8 cylinders were about 60psi even added a bit oil in the cylinders and still around 60psi like wtf, at that psi i wouldnt even think the car would start or run, and it starts and runs pretty good thats what confuses me. Any ideas?

 

[General karthief]

I would check the valve adjustment. You may need different push rods.
just my opinion and not based on any actual mechanical experience.

 

[dgollem]

With all cylinders close to the same, I would suspect the cam is out of time allowing the intake or most like likely the exhaust valve to stay open too long and bleed off compression through the valve. I don't know the specs of the tfs1 cam but old school hot cams would drop compression because the duration was longer. , The corrective actions was changing to dome pistons or some other compression increasing method, also the longer duration pushed the power band up the rpm range and the engine would be a dog at lower rpms. 60 psi seems low even for a long duration cam that's why I suspect cam timing,Jjst some thoughts, hopefully others will chime in.

 

[General karthief]

^^I agree, this is also something to think about^^

 

[zlightlystoopid]

I would check the valve adjustment. You may need different push rods.
just my opinion and not based on any actual mechanical experience.

For sure i will take the valve covers off and recheck my adjustments

 

[zlightlystoopid]

With all cylinders close to the same, I would suspect the cam is out of time allowing the intake or most like likely the exhaust valve to stay open too long and bleed off compression through the valve. I don't know the specs of the tfs1 cam but old school hot cams would drop compression because the duration was longer. , The corrective actions was changing to dome pistons or some other compression increasing method, also the longer duration pushed the power band up the rpm range and the engine would be a dog at lower rpms. 60 psi seems low even for a long duration cam that's why I suspect cam timing,Jjst some thoughts, hopefully others will chime in.

Hmm yeah that makes sense, you think it would help if i just advance the cam timing a couple degrees, i have the comp cams timing chain and it has the 3 key-ways on the crank sprocket to advance or retard

 

[dgollem]

For a point of reference I would do the whole top dead center drill and make sure the cam timing is right. being off a tooth will make it run poorly but should not cost that much compression. A couple of teeth maybe. Definitely at least check the alignment of the cam timing marks. Look up degreeing the camshaft. Also karthief may be correct if your push rods are too long they may not be letting the valves fully close. Did you change lifters to lifters, cams and push rods have to match, they don't always play well if you mix manufactures. Also I would check the valve lash adjustment if the rockers are too tight the valves won't close all the way either. Could also be a combination of the events.

Also double check that your compression gauge is good, it would suck to pull things back apart to find out later you had a mis-calibrated/broken gauge. The rough idle and misfire could be caused by other issues.

I just googled lost compression after cam install, there is a lot of information about making sure cam timing is correct and appenrenty a common mistake of using the wrong marks with multi keyway timing chain gears when lining up timing, also common to set it out by 180 degrees.

Keep us posted on your progress.

 

[zlightlystoopid]

For a point of reference I would do the whole top dead center drill and make sure the cam timing is right. being off a tooth will make it run poorly but should not cost that much compression. A couple of teeth maybe. Definitely at least check the alignment of the cam timing marks. Look up degreeing the camshaft. Also karthief may be correct if your push rods are too long they may not be letting the valves fully close. Did you change lifters to lifters, cams and push rods have to match, they don't always play well if you mix manufactures. Also I would check the valve lash adjustment if the rockers are too tight the valves won't close all the way either. Could also be a combination of the events.

Also double check that your compression gauge is good, it would suck to pull things back apart to find out later you had a mis-calibrated/broken gauge. The rough idle and misfire could be caused by other issues.

I just googled lost compression after cam install, there is a lot of information about making sure cam timing is correct and appenrenty a common mistake of using the wrong marks with multi keyway timing chain gears when lining up timing, also common to set it out by 180 degrees.

Keep us posted on your progress.

Oh yeah i will definitely try another gauge, if i get the same numbers then ill pull the timing cover off this weekend and see whats going on. Thanks man ill let you know!

 

[zlightlystoopid]

Guys! Okay so i tested the cylinders with another gauge and numbers are now around 150 psi so the other gauge was definitely bad, still need to find that terrible misfire tho any thoughts? Ive changed plugs and wires and the distributor and coil are like a year old

 

[2Blue2]

Also double check that your compression gauge is good, i

Way to go Dgollem! Nice call on the compression gauge being bad
It b hard to diagnose over the inters-web.

 

[dgollem]

Glad is was just the gauge. The misfire could be a lot of things based on what you describe since it's not valve timing related check for vacuum leaks next. keep us posted on the progress