360 Problems

[northplainsdrifter]

The last time out with the boys the CJ developed a problem. It was running great and then I mashed on the skinny pedal and right after that it developed a "miss". I call it a miss because it's hard to describe. It's like a real bad vacum leak. It hardly idles and when it does the vacum pulsates wildly. I plugged off the PCV valve, had the valve covers off and all is working good there. I've sprayed starting fluid all over and can't find a leak anywhere. I just took the Holley off and apart and it seems fine. I haven't done a compression check yet but I do think it is running on all cylinders. It has an Edelbrock Performer intake. My next guess is to pull the intake and see if the intake gasket went bad. Can they leak internally? I've never had one go bad so I'm kind of guessing at this point. Anyone have a guess what else I can check

[ironman_gq]

they can and do leak internally. you might have bent or burned a valve or pushrod or broken a ring. I would start with a compression test if it checks out move to the intake and valvetrain in that order. also check the timing chain for looseness or possibly skipped. I had a stretched timing chain skip on me once just far enough so that I had 0 compression on all cylinders happened after I wound it up to about 6k. a loose chain could cause erratic idle and the vacuum symptoms that come with it. it can also cause errativ ignition timing as well.

[northplainsdrifter]

The timing chain and gears are pretty new, maybe a year old and mostly off road miles. With the valve covers off I turned it over and all the valves are working fine. It still runs pretty good and doesn't smoke, that's why I'm thinking it is a BIG vacum leak somewhere.

[tufcj]

Even if the valves seem to be working OK, give each valve a good push, and look at the springs. A broken valve spring can still close a valve, but be sucked open under vacuum. It could cause the miss you describe.

Bob
tufcj

[ironman_gq]

so could a valve not seating properly. I would check the timing set to be sure. The replacement one I used the first time around had already started to stretch when I tore the motor down for a full rebuild less than a year later. some have flashing in the oil passage and dont get adequate oil. I would pull the intake first though and start with an intake gasket

[northplainsdrifter]

Didn't think to check the valves springs themselves. That makes a lot of sense to me on the sucking sound. Thanks for the info! That would be a easy fix too!

[northplainsdrifter]

I unfortunately found the problem today. Broken exhaust valve. Did a compression check and the last cylinder I checked there was zero compression! It is stuck in the open position, I'm guessing that's why I was getting pulsating vacum readings. The spring was still sitting like it was all there until I looked close with a light and didn't see the shaft of the vavle. The rocker was going up & down but with no vavle there. I'm going to pull the head tomorrow and see how bad it is. If the piston didn't hit it and make a mess of things, I might be able to just replace the valve.

I don't know how many miles on the engine so I'm wondering if it would matter what head gasket I should use to put it back together? I'm running a Edelbrock Performer and was also wondering what type of gasket set I need there. When I put it on originally there was the valley pan type and non-valley pan type. I went with the valley pan but they are more expensive. Do I need the valley pan?

Thanks for any input.

[JERSEYJOE]

Yes by all means. The pan part of the gasket keeps hot oil from splashing on the exhaust crossover and burning. Use of the non-valley pan gaskets is good for a race only motor or any motor where the exhaust crossover is blocked. People that have tried to omit the pan type gasket will experience an mysterious oil consumption problem on the order of a quart every 200 miles. Been there done that. What happens is the oil hits the exhaust crossover, vaporizes and gets sucked up the in the PCV system. The shield that is riveted to the intake also helps to control this.

[ironman_gq]

If the shaft isnt there where did it go? did the keeper pop off and fall into the oil pan or did the shaft break and the valve fell into the cylinder :shock: If its in the cylinder I would be concerned for the piston. Make sure to post some pics if its broke good :razz:

[northplainsdrifter]

The vavle broke right under the retainer clips and the spring stayed in place and looked like it was working. The vavle slid down, hit the piston and bent. Very minor scoring on the piston. I'm going to just try and just replace the vavle and put it back together. It's an older motor and I have no idea the miles so I'll just hope it last for a bit!

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[ironman_gq]

did it mess up the valve guide at all? :shock: I would at a minimum measure the valve guide and make sure its not ovaled or screwed up in any way or you might end up with a stuck valve and more problems. cant be too much to have the guide replaced if its bad

[northplainsdrifter]

Good idea! :lo1l:

[northplainsdrifter]

I threw in a new vavle, new gaskets and it's running! Time to go out and see how it's gonna hold up. I think I'll try keeping it under 6000 rpm for awhile. :!:

I really scored on a 360! Found a complete running engine for $400 that has about 30,000 on a rebuild! It has a brand new Edelbrock 1406, Performer intake, Crower Pro-Comp cam. He also gave me the headers, alternator, power steering pump, 2 clutches, radiator and the engine stand! SCORE!!! :!: He said he didn't like all the power. 111!!! I didn't think you can have too much! LOL

Now I'm not too worried about how my old motor will hold up.