Cylinder compression 150 per cylinder good?

I can only give the advice of an advanced rookie............ I believe that some compression can be due to carbon build up on the top of the piston or in the combustion chamber of the head - but I think that most of the difference is probably in the compression gauge. I doubt if any 2 gauges will be that close, especially after banging around in a tool box for

15 to 20 years. I would still ask around - or wait for more posts from others - but the "no variance" part sounds good. I would think that if there was a problem, such as carbon build up, it probably would not be even across all cylinders. Other possibilities might be a milled head, thin head gasket, different pistons, etc. how many miles on the engine ? & what has been done to it ?

Very few gauges are accurate or will read the same on the same engine.

If they are all even, that's a good thing. Too high can mean carbon buildup.

Normally carbon isn't a problem until you start to get spark knock or ping or until it starts dieseling or running on after the key is turned off.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

William Oliveri wrote:

Don't know the mileage as the engine was put in used when the previous owner poured water on the overheated engine and did something bad. The only thing other than stock is the Mopar MPI kit.

Bill

Anyway to clean carbon build up? Is there any product available to do this?

Thanks,

Bill

I like to smoke out my neighbors just to piss one off and use a pint of ATF poured very slowly down the throat of the carb to burn the carbon away.

I get the engine hot and slowly pour it in while keeping the rpm up with my hand on the throttle linkages. You don't want it to stall.

This method works excellently and makes them clean like new inside. I have opened them up after. I use that as a prep before a head gasket job too.

I have been told by lots of folks that a pint of water poured in the same way will do the same job minus the smoke cloud. ATF does make one serious cloud of smoke...

If it isn't pinging or dieseling, then a good hard day wheeling with some high rpm or a hard highway run will clean them out good too.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's

William Oliveri wrote:

Carlo has is right. Unless the compression gauge you have has been

*calibrated* > I can only give the advice of an advanced rookie............

that can really screw up the o2 sensor ya? I've done the water thing a few times. Nick

No, no damage to the O2 or cat.

I have worked in several garages that used the ATF treatment for city driven cars as part of a full tune up. No damage was ever reported.

They even sell a product in a spray can for this and it smokes like ATF.

Mike

Nick N wrote:

My understanding ,,, water creates steam ,,, which may remove the oil from parts like valvestems, rings and so on ,,, which is not good. If it was me and I had a carbon problem, I'd first figure out what was causing it, then fix it (not that I haven't had a few old beaters that carboned up regularly).

And if I had 150 out of 140 ,,, I'd consider myself a lucky guy and go buy a coupla lottery tickets :-)

That means you engine is good and strong. I wouldn't worry about the 150 number, I would worry about large variances among them. The tester he used could be out of calibration enought to read a few psi higher than it should. The relative difference among adjacent cylinders is more important than the actual numbers you get.

diagnosised

Me too. I wouldn't give it a second thought. I would spend the time it takes to pour water or ATF down the intake to get to my favorite wheeling spot. ;-)

Fantastic!!! I'm stoked. I'm making a cross country trip to Florida in March and was worried about the condition of the engine.

Thanks all,

Bill

My book says 150 and my old one had 145 all across when I replaced it with a lower mileage one.

Mike

bowgus wrote:

diagnosised

A compression test tells only a small part of the story you should have do a leak down test on every cylinder but what do I know?

Dont know what you drive, but my mechanic has me use a product called BG Carbon Cleaner (aprox $25 a can) for my fuel injected car, one cylinder was reading a lot lower than the others. He suspected carbon buildup. One can of the cleaner and it cleared right up and they all read very close the last time I had him check it.

I got hooked on "Carbon Guard". My neighbor used to be an instructor @ OMC (they make Johnson boat engines). My Scout was spitting & coughing because the #8 cylinder was oil fouling. He brought over a couple of bottles for me to try. He poured a full bottle down the carb & said to use one oz/15gal of gas in the tank. It was still pretty bad for about 2 tankfuls after that & I was getting ready to just give up & rebuild it. I was low on money & didn't want to but it seemed as if I just didn't have any other choice. AND THEN......................it was a miracle. I was coming home from work, it was dark & I was tired, & all of a sudden the engine started bucking, & backfiring. I didn't think I was going to make it home & began to look for a place to coast to a stop on the side of the road. As quickly as it started spitting & choking, it just, all of a sudden smoothed out & purred. Swear to God - I shit you not..........It won't run more than 2 tanks of gas without it. I have a 32 gal tank & put an oz or 2 every time I fill up. I use it once a month or so in the other vehicles. It works for me - costs $10.00/12oz btl - & you only use 1oz/15gal - and you get it @ any johnson outboard dealer

Funny, I went back and double checked and yes, the FSM says 120 to 140 but I have another, newer training manual for the I6 4.0 and 4.2 and there, for the 4.2, it says 120 to 150 so I guess I'm right in line.

bill

As all of the others have said, don't worry about the 150 reading. Too many variables that will change the reading. Most specs don't give an actual number but rather give a % that they should be within to each other. A word of caution about removing the carbon. The water and ATF methods are commonly used but you need to know what you're doing. If you pour it in too fast it will hydraulic the cylinders and probably do serious damage that you won't know about for a while. You can not compress a liquid so if you dump too much in too fast it will sit on top of the piston and jam it up when the piston comes to the top. The engine will stop suddenly in the worst case, but may not but will still do damage. Sudden stop of the piston like that or hammering it with this liquid on top has been known to frequently bend the connecting rod. It won't break it and you won't know it's bent but now the load will be on one side of the rod bearing instead of spread evenly across it. In a few thousand miles you've got a mild con rod knock. Gets worse until either you straighten the rod and replace the brg or it spins in the rod and takes out the crank too. Another thing that I have seen happen is when the carbon breaks off if it's really badly carboned, the pieces may be large enough to actually sit on top of the piston in a spot of close tolerance and start pounding against the head. I've experienced it where you're doing the de-carbon with water or whatever and while you're pouring it down all of a sudden it will start knocking like crazy. Very loud and very solid. Most times it will go away after a few minutes, but you may have bent the rod in that short time. I've also seen the carbon piece lodge under a valve and prevent it from closing and have to remove the head to correct it. These are all true stories. I know there's a lot of rookies and wannabees that read this board, so be carefull out there. In this particular instance with a cross country trip planned I would do nothing. If there's a carbon buildup the safest method of getting rid of it is a good long run at highway speeds. Steve

"William Oliveri" wrote in message news:bu1c4l$c8dq2$ snipped-for-privacy@ID-193866.news.uni-berlin.de...

diagnosised