How can tell what is causing no compression on number 1 of a 302 75 Mav? Would this cause it not to start? Thanks Bob
Take of the rocker covers ... my guess is a valve stuck open for some reason. If the the other 7 cylinders are good compression it would more than likely still start and run ...
No compression #1, 3, and 4 and only showing 30 in #2. Not sure how good the tester is. Does this mean head gasket or could it still be rings or other stuff? Any way to know for sure Thanks Bob
Do you know if the timeing chain is good??? a jumped chain will cause this condition.Also a worn out engine will show this sort of compression problem.Weak rings/bad valves(burnt,bent or stuck open)bent push rods will do this also if they are not allowing the intake valves to open or open enough.if you have access to compressed air you could pump air into the cylinders individually with the valves closed and listen for air hissing in the exhaust or in the crank case or out the carb.How many miles on this engine??? did it just start doing this or has it been a poor runner from the get go???A cam shaft with wiped out (flattened lobes )will cause this also.
When I got the car it was not running because of a duraspark issues(no spark). The guy said the timing chain only has 200 miles on it and that he did a valve job to it. The motor has in the 90's. The #1 and #5 rockers and push rods are rusty like, so I'm not sure if he let it sit without the valve covers. I'll try to get a picture I have a compressor. How do I test the cylinders? I assume a leak down kit, but not sure. What position does the cylinder need to be in to do the test? Thanks
If you have the valve cover off.Visually inspect the valve train,look for loose rockers,bent push rods, valves that are hanging open.If all seems good,loosen the rockers so all the valves are closed and look for any that arent sitting at the same level as the others.use a straight edge accross the tops of the valve stems or spring retainers if you have too.If all still checks out good,pull all the plugs.Inspect them as you remove them.Plug condition can tell you alot about engine condition.I assume you have a compression tester,if you have the rubber hose type,the threaded fitting on one end and a quick coupler to attach the gage at the other end you can use it to pump air into the cyl bores(some have a schreader valve in the hose,remove it for this test).Just bring each piston to top dead center(or close to it)hook up the hose and put about 30 psi into the cyl and listen for air escapeing out the exhaust/crank case or carb.If it comes out the exhaust... bad exhaust valve on that cyl...if it blows into the crank case (you will hear it come out the valve cover) then bad rings/piston... if air comes out the carb,bad intake valve... Hope this helps you out,good luck.
I've added a gallery. The first rocker on cylinders 1,3, and 4 are loose. How can I tell if I have a bad cam versus stuck valves or other. The close up is of #1 http://mmb.maverick.to/gallery/showimage.php?i=7066&c=6 http://mmb.maverick.to/gallery/showimage.php?i=7067&c=6 http://mmb.maverick.to/gallery/showimage.php?i=7068&c=6 http://mmb.maverick.to/gallery/showimage.php?i=7069&c=6 Thanks
With all the rockers properly pre-loaded,you can spin the engine and look to see which valves dont have the same amount of movement as the others(this will tell you if you have a wiped lobe).check to be sure you dont have any bent pushrods first.If you loosen the rockers(take all the load off them and you have valves that are not closed)sitting at a uniform height you have found your bent/stuck valves.Now you need to determine what caused it and check your pistons.valves dont just bend by themselves something causes it... pistons get too close and bend em.This is caused by too much lift on the cam.Pushrods too long,or you overrevved the engine and floated them into the pistons.Less likely is lifter pump up which effectively turns a hydraulic lifter into a solid lifter removing the built in lash and creating too much lift.I would pull the intake at the least and look at each lifter bottom and cam lobe if all else checks good.Its hard to tell but it appears that the closest valve in the close-up is open a bit.Soo its stuck/bent.you need to determine what caused it.
If a valve is stuck open what is the best way to loosen it? I will check it out some more, but considering the car sat for a year give or take a few months if wouldn't surprise me. No bent push rods If I take the load off three valve look to be open. Believe it or not I'm enjoying trying to get this car running. Thanks for all the help!!! Bob
You can tap it with a hammer and see if it moves or closes.If it does either,hit it a few more times to loosen it up in its guide(try squirting some oil on it)and work it loose.You need to pull the head to correct the problem if it wont move.It may be rusted to the guide.OR its bent(hope not)If it moves when you hit it but wont return to the closed position its bent.Make sure that piston is down in the bore before hitting the valve,or you may bend it yourself trying to fix it if you bounce it off the piston.If it does prove to just be stuck.Work it loose and check out all the others to be sure.Sometimes they loosen up and work fine and sometimes they act up after a while if not immediately.I agree, digging into an engine to get it working can be fun.Just go slow and be deliberate...and keep asking questions...Good luck,and have fun.
