Guest Anonymous Posted September 11, 2002 Share Posted September 11, 2002 If all the compression is up with a slight discrenancy in #4 and a bent valve was an unsuspected culprit in #6 and your oil burning concerns were focused on # 5 which by all accounts appears healthy consider those little round rubber valve seals by allowing oil into #5.. your valve and seats may have been crudded up with bad gas residue preventing them to fully close.As for oil loss, I have encountered oil leaks especially around and in the oil pressure sending unit to account for a goodly amount.As a precaution replace the valve seals on all the valves.Slap the head back on and see what happens. You will have to installthe head to do a leakdown test. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 12, 2002 Share Posted September 12, 2002 I've sent the head off to a machine shop to have it rebuilt. I thought the same thing, that the oil was leaking past valve seals or guides, but the machine shop guy says that other than the bent valve the head looked fine and shouldn't have been leaking... Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 12, 2002 Share Posted September 12, 2002 This one's kinda long... sorry guys. Okay here's the quick background... I transplanted an L28 into a '72 240 that had been sitting for 13 years. The mechanic drained the fuel tank and put new fuel but didn't advise me to get the tank cleaned before driving. Bad fuel residue caused a big problem... valves getting stuck left and right. I got it cleaned out but afterwards there was some bad valve tap that wouldn't go away after the valves were adjusted, so I figured either a bent valve or damaged valveguide. After about 2 mos. of driving it like this (I didn't have the cash to get it pulled and rebuilt until now) I had dropped it off to get some electrical work done, and when I pick it back up the guy informs me that the engine is smoking a little. Now I know for a FACT that it was not smoking at all when I dropped it off to him. I had actually watched him doing some work with the motor running, I was standing behind the car (the tailights weren't working), and didn't see anything. Well anyways I get the car home and pull the spark plugs and sure enough the #5 spark plug has some deposits and oily coating. However, I also noticed that there was some oil leaking down onto the plugs from the valve cover, mostly onto the #5 and #6 plugs. I cleaned everything up, tightened the plug extra tight and the valve cover also. The smoke at idle was gone, however it would still blow a puff of smoke on sudden acceleration, or between shifts on hard acceleration. Just one puff, not constant smoke. Anyways, the head was pulled and dropped off at the machine shop yesterday... we could plainly see that oil had been getting into the #5 cylinder. I just assumed it was either the problem with the leaky valve cover, or a problem in the head as A) I already knew almost for certain that at least one of the valves had gotten bent, so I figured a guide or seal could just has easily have gotten damaged and the block is rebuilt with only about 20k miles on it and on a compression test about a month ago all cylinders read relatively even (actually the number FOUR cylinder read a tad low, just 10 psi short of the rest of them, well within limits... but it's the number FIVE that's burning oil). Well I get a call from the machine shop today saying that yes indeed one of my valves was bent... the intake valve for cylinder number six ... (this just keeps getting wierder... when I did the comp test the #6 cylinder had actually read the HIGHEST of the bunch!!!). He says otherwise he didn't see anything wrong with the head... well nothing that would cause oil burning anyways. So he suspects a broken or bad piston ring. The question is, now that the head is off, is there an 'easy' way of checking this out? I don't have the cash to get the block dissasembled... but at the same time I don't feel right about throwing a rebuilt head back on a bad block. Is there a good method for checking the rings with the head off or do I just put it back on and then do a compression or leak down test? I'd really like to check this before putting the head back on... I need some opinions guys I'm really low on cash and limited on options... and really pissed this isn't supposed to happen after 20k miles. By the way, I don't know that it matters but the piston tops and cylinder walls look fine, minus some carbon build up on the piston tops. The head gasket was fine, looked near brand new still, and didn't need to be scraped off at all. Quote Link to comment Share on other sites More sharing options...
Tim240z Posted September 12, 2002 Share Posted September 12, 2002 I assume that you are going to put in new valves and guides? If so then obviously you will be putting in new seals! That should take care of any smoking issues. From the symptoms that you described, it is very likely that the seals were bad. As long as the head is still in good shape (which it is according to your shop), then problem solved. Make sure that the shop checks the head deck for straightness and skim if necessary, and remember to retorque the head after 500 miles or so. HTH. Tim Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 12, 2002 Share Posted September 12, 2002 Rarely have I been able to identify a bad valve seal by looking at it.. What will give a bad seal away is: after the car has set overnight without the engine being started.. the first time it is started the next day.. a large PUFF of grey smoke will momentarily come out the exhaust pipe on initial start up. If the engine was shut down with the offending valve closed, there would be a good chance there would be no puff of smoke much later on the initial re-start. I forgot what a puff a smoke out the exhaust means during transmission shifts. (Rings?) Quote Link to comment Share on other sites More sharing options...
Tim240z Posted September 12, 2002 Share Posted September 12, 2002 Rarely have I been able to identify a bad valve seal by looking at it.. Why bother even trying to look for one. They are so cheap, that even if I knew they were all good, if I had the head apart I would replace them!!Puff of smoke on shift is the same thing 'cause you generally accelerate when shifting, so I'm 99% sure it's valve seals (assuming the smoke is blue).(white smoke is water in chamber, black smoke is rich fuel/air mixture...a little oversimplified, but 'generally' true) Tim Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 13, 2002 Share Posted September 13, 2002 Heheh of COURSE I'm gonna have the seals changed either way!!! The only reason I was asking if you could tell if they were bad or not is that the machine shop guy said as far as he could see, there was nothing wrong with the head that would have caused me to be burning oil. So I just wanted to know if that meant 100% for sure that it wasn't a valve seal. Because if that's true and it absolutely was not a valve seal then than leaves a very good chance that it's piston rings... which would be very bad news for me. But from what you guys are saying it could have been a valve seal... it just might not be apparent by looking at them. And by the way I was getting a puff of smoke on startup as well... Quote Link to comment Share on other sites More sharing options...
Guest Anonymous Posted September 13, 2002 Share Posted September 13, 2002 With the head off you could pull the pistons and check the rings and even replace them if needed soumds to me like valve seals. Get Nissan OEM seals which are good Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted September 13, 2002 Share Posted September 13, 2002 Anyone else have any tips? If a rubber valve seal was letting oil leak past would you be able to tell something was wrong by looking at it? If the head was all taken apart, I mean. Quote Link to comment Share on other sites More sharing options...
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