I went to the track last night and the car was running really good. The night air was cool and I ran some of my best times in time trials...15.25 and 15.26...all was good. Then first round came around and I dialed a 15.25 but lost the race to a 10 second car at the stripe. I stop to get my time slip and it is idling pretty rough and the car slowed to a 15.42 on that pass. I check the carb and timing at the track but still idling rough. This morning I pulled the plugs and they all looked pretty decent...a few were a little dark. I pulled the valve cover and everything looked fine. I decided to check the valve lash and every one was quite tight...couldn't even get the feeler guage in there. So I re-adjusted all the valves, check air fuel and timing and it is still idling really rough. Now what? Could a blown head gasket between adjacent cylinders be causing this? Is there a way to tell without pulling the head?
Put a vacuum guage on it. This is a good link. Should help narrow down the rough run. http://www.secondchancegarage.com/public/186.cfm Did you try a comp. test yet.
Got a compression test gauge ? That would be best imo, that way you narrow it down to which two cylinders it is.
UPDATE: This morning I did a compression test and the results are disappointing. The number 1 cylinder is only reading 60-65 while all the others are 155-160. I'm not sure what this could mean. This is a fairly new build so I'm not sure what to think.
Hey Gene Try putting a few shots of oil in no.1 cylinder through the plug port and run your compression test again on that cylinder, if the compression does't come up then you may have a valve-train problem, ie: bent valve, bent pushrod, broke rocker-arm, rocker-stud pulled up if you don't have screw-in studs. If the compression does come up then you probably broke a compression ring. Just a thought. BobbyB
the oil thing above is a really good test. its called a wet compression test. a leak down test is very help full here also. you need access to an air compressor to do it. if you dont have access to a leak down tester you can do it with the compression tester hose. you need to put the cylinder your testing right on top dead center. if your using the compression tester hose you need to pull the valve core out of the end of it. its a schrader valve just like in a tire valve stem and a tire valve stem tool will work. screw in the hose to the spark plug hole and hook the hose to the air compressor. if you have it on top dead center the motor wont turn. if you dont the motor will turn over till the piston is all the way down. it may take several attempts. now you will be able to hear the air escaping past the gaps in the rings into the crank case. if you have a bad valve you will hear air coming out the carb or exhaust. this should tell you exactly what you need to repair.
UPDATE: I didn't think much about the fact that the week before my issue I was racing and I kept blowing my valve cover breather off. So before the last race I replaced it with a snugger fitting one. Problem solved...well sort of...it didn't blow off any more but......when I limped home from the last race and looked at it the next morning I noticed oil splashed on the side of the block and on the oil pan and converter cover. The motor doesn't leak a drop of oil so the only place it could be coming from was the dipstick. When I told my machinest about this he told me that most likely I have broken the ring land on the number one piston and there is so much blow by going into the crankcase and forcing the oil out the dipstick. Crap! A little history is I blew the head gasket a month ago on the chassis dyno on the number one cylinder. This may have caused an extremely lean condition and hurt the piston.
Probably just do a little at a time since it is getting so hot out. I have no time frame to get this back together since I don't normally race or drive it that much in the summer months.
I finally got the head off last night and was hoping to see signs of a blown head gasket on the pushrod side of the motor...nope. Head gasket looks good but completely covered with oil. The previous head gasket was in the same condition...covered with oil. Not sure what to think of that. Also this time the top of every piston is covered with oil. Could doing the compression test caused oil to get up on top of the pistons? One good thing so far is I turned the motor over to get the number one piston at the bottom of the stroke and the cylinder looks perfect...no scoring or any signs of carnage. Just to make certain the head is ok I am going to take it to my machinest to have him check it out. Assuming that is ok then the next step is pull the motor and take the number one piston out and see what's going on there. I hate it when things break!
