For the past few weeks I've been trying to get this 351C running decent. 1st I replaced the lifters that were almost all collapsed then I had fun tracking down a lot of vacuum leaks(main was the carb base & no vac line on the vacuum modulator!). Well a buddy said to me the other day, you should take a compression test on that old engine-it's 100% stock & never been apart, but always has this chugging idle to it no matter what. Well here are my dismal readings in both dry test & wet test: DRY: (1)180 (2)180 (3)160 (4)150 (5)175 (6)0 yes, zero! (7)130 (8)130 WET1)170 (2)220 (3)205 (4)160 (5)195 (6)5 yup five! (7)180 (8)170 It seems the #6 cylinder is dead, no compression & none either when I added a bit of 30wt oil for the wet test. (I don't consider a measly reading of 5 anything to get excited about!) Now I'm no expert on testing, but when the cyl #'s don't jump much like in #1, #4, #5 cyl does that mean those cyl's are holding compression ok compared to say #2, #3, #7, #8 ??? Then there is the dismal #6 cyl with ZERO COMPRESSION & ONLY 5 ON THE WET TEST!!! Think I found my chugging problem with this motor...
now you want to do a leak down test on that cylinder. thats where you put compressed air in the cylinder and see where it comes out. it will come out the exhast or carb or valve cover breather. if its the exhast or carb then you just need to get a valve job on that head. if its the breather then the rings or piston are really damaged and will need a rebuild
IMHO I believe that it is time for you to tear the motor down for a rebuild with numbers like that. If you do perform a leak-down test make sure you warm the motor up by running it until it gets to operating temp. It looks like for the most part when you took the compression dry that cylinders 6, 7, and 8 are low, but when you put oil in the cylinders all of them (except #1) increased.................this is a pretty good indication that the rings are on their way out. Even #6 responded in an upward climb..............5psi is a far cry from 0 and does indicate a sealing problem. Could the valves be a part of this story................sure they can, and as I said it would appear the whole motor needs some attention. How old is the motor, what was it like when you got it, and how long have you driven it in this condition? When was the last time you changed oil and filter? What did the oil look like and smell like when you took it out? These are all questions to better understand what is going on with the motor..................IMHO
Agreed with the above. Even without the dead cylinder the numbers arent good. I'm assuming your valve adjustments are OK?
Well all-thanks for all the input. I know it just needs to be yanked & rebuilt w/readings like those but I'd like to really do the leak down test. The motor was from a 70 Cougar that was last run in 1986 according to the license tag. The motor when we pulled it is 100% bone stock, we did add a performer 351 & 600 cfm carb we had & new water pump. When I pulled the oil pan there was a lot of sludge & pieces of valve stem seals-alot! Cleaned it all out then pulled the valve covers & the same crap in there too & under the intake also-this motor was just driven & driven & never taken care of, how sad... After all this prepping & cleaning of this motor it has been only driven about 100 miles or so here & there & that's where I'm at right now-this thing just chugs along & smoke coming out of the breather cap like a train, chuga chuga chuga & sometimes even a boom from the carb too! I do have a nice set of 351C heads that are decent-would putting those heads on at least get the motor by until a rebuild next year?
After hearing the history on this motor I hope you didn't pay much for it. I don't mean to be hard, but when you pulled the pan off you should have checked some or all of the rod and main bearings...............but with the valve seal pieces in the pan this should have been a clue that at least the top end of the motor needed serious attention. My guess is that if you had pulled the bearings you would have seen they need attention also. As for putting the rebuilt heads on the motor I feel it would be a waste of time, because I don't think it would change much of anything.............and with basically one dead cylinder and running it that way there is a chance you could destroy the motor. I know you don't like to hear this, but I would take the motor out, tear it down and find out if you should be rebuilding this motor or stard looking for another that is more useable.......................the other thing you could do if you can't afford to rebuild the motor now would be to tear it down, clean the block, have someone find out what kind of clearances you have, and if they are not too bad, just put new bearings and rings in the motor and slap it back together and then use your good heads. Or, I wouldn't normally tell anyone this, but go to auto parts store in your and try some Rislone, http://www.barsproducts.com/100QR.htm or other product that when mix'd with you oil or put down the cylinders may help free any stuck rings or valves (this will not help your valve seals which sound like they are totally gone)................but it would be a very cheap way to see if you may be able to improve your motors performance..........although it sounds like the motor is beyond this kind of help........."You never know unless you try". Otherwise you are faced with a complete rebuild......IMHO
Thanks all, & to olerodder for the last post. For now I'm just going to pull it & a buddy has a decent running 351C he'll let me borrow/trade & that's what I'll do for now. I'm still going to tear into this thing, very curious about that dead cyl. Again, thanks all...
Agree I took my 351 Cleveland in for a rebuild and it came out as a 393 Cleveland I don't know what happened
Thanks, and keep us advised as to what you find out because now you have my curiosity up also. Also, post some pictures as you tear it down. Tearing down an unknown motor (condition) is almost like opening presents at Christmas..............kind of exciting............IMHO
