Knucklehead97 Posted September 15, 2015 Share Posted September 15, 2015 A couple months ago I took my MJ to a mechanic to have it checked out because I could not find the source of the little puffs out the tailpipe when it got warmed up. They, too, could not figure it out. But told me they THINK it's a burnt/bent/collapsed valve. This sounds probable considering my Jeep has cracks in the exhaust manifold and a good exhaust leak before the muffler. Lack of back pressure could have screwed up a valve, eh? Also for about 4 months I ran it on 5 cylinders with my #1 cylinder having an injector that was to lean and wouldn't hit unless I was on the throttle. Don't know if that could have done anything, but, this begun after I changed injectors and started firing on all cylinders again. Far as I know this did not happen beforehand. But anyways, if I do have a jacked up valve then what are my options? How much would a valve job be and is it easy enough for me to do myself if I got the parts? Or could I just get a valvetrain off of a good running engine and swap it on with new lifters and call it done? This all will be done after getting the leaks fixed, of course. Just looking for the simplest option. Link to comment Share on other sites More sharing options...
Akula69 Posted September 15, 2015 Share Posted September 15, 2015 Obviously, a valve job can be expensive, especially if you have to get the seats re-ground (I would not recommend trying a do-it-yourself seat re-grinding). if not too bad you can lap the seats with paste and a lapping tool but that is slow tedious work. Exhaust valves are approx. 13.00 each from Rockauto, the intake valves slightly more, but replacing the valves requires at least a decent lapping job. In all cases you should replace the valve guides, (Felpro set is about 14.00). Getting a replacement head is an option, but can be pricey for the upper end models. Getting a replacement used head is a crap shoot, unless you pull the valves and check them. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted September 15, 2015 Author Share Posted September 15, 2015 Dang, this really sucks, honestly. I appreciate the input! If anyone knows any cheaper routes or anything let me know, please. I'm interested in all options if it is actually a jacked up valve. Which, I won't know for awhile anyways. I've been driving the thing a bit before my tranny went out and it has plenty of power and does great unless it's idling. Link to comment Share on other sites More sharing options...
Eagle Posted September 15, 2015 Share Posted September 15, 2015 IMHO you have nothing to lose by trying a valve job on your own. If there is a seat that needs to be cut, that's a job for a machine shop. However, it's entirely possible that simply re-lapping the valves to the seats will resolve most of the issues. War story: A long tiime a go, my ex-wife and I had a 30-foot sailboat. The engine was an inboard, a little 4-cylinder gasoline job called the Atomic Four. Paid a yard to service the boat before putting it in the water one year. Halfway through the season, the engine started losing power. It kept getting progressively worse. Followed things through and found that the yard had not replaced the fuel filter, it was almost completely plugged, and the engine had been running very lean because it was starving for gas. Replacing the fuel filter helped a little, but not much. Ran a compression test, and one cylinder was barely above sero. Obviously, the lean run had burned a valve. We limped through the season, and that winter we put the boat up for sale. Found a buyer who loved the boat. I disclosed the engine problem to him, and he was okay with it. The price was negotiated to allow for having a valve job done. But ... I was in Connecticut, and the buyer was from Pennsylvania. He wanted to take the boat from Connecticut (Long Island Sound) to Maryland (Chesapeake Bay) to have his yard make the repair, but he was afraid the weak engine might not get him through the currents around NYC (Hell Gate). So I agreed to do a quick-n-dirty valve job just to get him to his home port. There was an old-time auto parts store and machine shop in the town where we lived, and I had become friendly with both the owner and the counterman. The counterman was a former Coast Guardsman, he doubled as a machinist, and he was familiar with the Atomic Four. The engine was an F-head -- valves in the block, not the head. He agreed there was a burned valve. The shop actually stocked valves for the Atomic Four because it was such a popular engine. I worked out a deal with the shop owner that I could hire the Coastie to help me with the work if I agreed to buy any parts from the shop. So we went down one Sunday morning and pulled the head. Sure enough -- badly burned exhaust valve. Too far gone to save, so we went back to the shop and grabbed one valve, and a head gasket. We didn't recut the valve seat, just dropped the new valve in and lapped it, and slapped the head on. Compression check looked good, so we called it a day. Coastie's price? A case of his favorite beer. The new owner reported at the end of his first season that the engine ran so well he never bothered to have the valve job re-done. So that's the moral of the story -- all it'll cost you to try is some time, some lapping compound and a suction cup, and a head gasket. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted September 16, 2015 Author Share Posted September 16, 2015 That's really inspiring, actually. I'll have to tackle this when I get past the AX-15 swap and RMS change. I'm guessing I only need to change and lap the valves that need it? It's not a "change one change all" type of deal? And from what I understand I won't even have to pull the intake or anything right? Link to comment Share on other sites More sharing options...
Eagle Posted September 16, 2015 Share Posted September 16, 2015 I'm guessing I only need to change and lap the valves that need it? It's not a "change one change all" type of deal? How many miles are on the engine? Link to comment Share on other sites More sharing options...
cruiser54 Posted September 16, 2015 Share Posted September 16, 2015 A test with a vacuum gauge will determine if you have a valve issue or an injector issue along with bad valve seals. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted September 16, 2015 Author Share Posted September 16, 2015 225000 miles on it. And I'm going to bring it up to the shop for a compression test and all that to see if the valves are the cause once I get my transmission installed. The shop does free compression checks. Or is the test with a vacuum gauge different from checking through compression? Link to comment Share on other sites More sharing options...
Eagle Posted September 16, 2015 Share Posted September 16, 2015 With 225,000 miles on the engine, it doesn't owe you anything. I wouldn't put a lot of money into a full, professional valve job on a high-mileage engine without doing the rings and bearings at the same time -- in other words, a full rebuild. IMHO you're a perfect candidate for a quick-n-dirty valve job in the driveway. If it works, you can drive it for another 50,000 or 75,000 miles. If it doesn't work, you're not out a lot of money. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted September 16, 2015 Author Share Posted September 16, 2015 I just don't have the money to change the engine if it doesn't work, honestly. This transmission change and having to get new tires has broke me lol. I'll have to look into the driveway job. What are the chances of the lap job fixing it? Link to comment Share on other sites More sharing options...
cruiser54 Posted September 16, 2015 Share Posted September 16, 2015 Refer to post 7 for how to VERIFY what the problem is. Link to comment Share on other sites More sharing options...
metrictonner Posted September 16, 2015 Share Posted September 16, 2015 Backpressure? Nice to mention backpressure since most of it is garnered from a good catalytic converter, which no one ever changes and most simply rip out anyway, along with EGR and O2 sensor, which is what you really need backpressure for. If there are no billowing clouds of BLACK smoke coming out of the tailpipe I would go for new, dual heat range (separate intake and exhaust), valve seals, not the one size fits all kind. Link to comment Share on other sites More sharing options...
Knucklehead97 Posted September 17, 2015 Author Share Posted September 17, 2015 Backpressure? Nice to mention backpressure since most of it is garnered from a good catalytic converter, which no one ever changes and most simply rip out anyway, along with EGR and O2 sensor, which is what you really need backpressure for. If there are no billowing clouds of BLACK smoke coming out of the tailpipe I would go for new, dual heat range (separate intake and exhaust), valve seals, not the one size fits all kind. yeah... my cat is gone and the pipe I installed in its place has a leak now which I'm guessing is what has burnt a valve IF I have, which I will find out ASAP. Also my EGR is soon to be taken out as well. And no smoke at all, not even white smoke thankfully. Just little pops at idle. Link to comment Share on other sites More sharing options...
88mjblue Posted September 17, 2015 Share Posted September 17, 2015 a good tip from cruiser: do a vacuum gauge reading, you can easily see if you have a burnt valve or not, or any other problems. Link to comment Share on other sites More sharing options...
cruiser54 Posted September 17, 2015 Share Posted September 17, 2015 Click on this: http://www.gregsengine.com/using-a-vacuum-gauge.html Link to comment Share on other sites More sharing options...
64 Cheyenne Posted September 17, 2015 Share Posted September 17, 2015 IF you replace a valve, I support the "lap one, lap them all statement" lapping valves is easy, you'll use a compressor to get the keepers out for the first valve, might as well do them all.. Beyond that, I've put a head upside down on a bench, put oil in the combustion chamber, let it sit overnight, in the morning, check the runners for leakage.... Link to comment Share on other sites More sharing options...
Knucklehead97 Posted September 18, 2015 Author Share Posted September 18, 2015 Click on this: http://www.gregsengine.com/using-a-vacuum-gauge.html that's very good info, thanks! I was at a weld shop today getting a bolt welded on my shifter because the yard I got the AX-15 from cut the shift threads off and there was a machine shop behind the weldshop. I went ahead and got a quote, just for the heck of it. Guy said about $150 for a full valve job/checking the head for cracks if I brought it to him. And around $20 to have a single valve ground down and reseated. Not bad prices, honestly. But I'll make the decision after doing a vacuum check and figuring out the actual problem. I appreciate it, guys :D Link to comment Share on other sites More sharing options...
Knucklehead97 Posted September 18, 2015 Author Share Posted September 18, 2015 If lapping turns out to be as easy as it seems, then chances are that's the route I'll go. Maybe I can find someone around here that has done it before to give me some pointers :D Link to comment Share on other sites More sharing options...
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