304 Issues

Hopefully I can get some help here.

Five months ago I decided to put the Jeep in the shop for complete restoration on the engine. The mechanic was recommended by a friend. In the beginning we all thought the man was honest, five months later (when he still has the Jeep) we find out that he is not. The block was sent out to the machine shop & his statements were as follows; 1) the cylinders did not have to be bored out the walls were clean & a little honing was all it took. 2) The pistons were replaced with standard equipment 3) the camshaft was replaced with a standard cam (I had a mild cam in the engine prior, not sure which cam was it was) 4) lifters replaced with new hydraulic lifters 5) heads were cleaned and new valve guides, seals, etc



Now that I have the Jeep back in my possession… I’ve spoken with the shop that did the R&R on the block… they confirmed the following for me; pistons are 40 over, everything replaced with standard parts, cam is stock cam (looks old though). This weekend we looked at the rest and know that the lifters are new, rods were old (replaced with new standard rods this weekend), rocker arms look like they were left outside to rust (****ed about this, they were perfect when I brought the Jeep to him, so I want to replace them with a good set of roller rockers). I’m running an Edelbrock Performer intake, Edelbrock Performer 600cfm carb, MSD Distributor (matching dist & cam gears), standard timing chain set, known good timing cover (oil pump is perfect), long tube headers (a few minor small holes at a couple welds, need to be replaced).



As is the Jeep will crank right up; however, once it warms up, I start getting some backfire out of the carb and a couple times it has overheated, shut down and we had to wait for it to cool down before it restarted. The timing is set to spec (5 OTDC). Ultimately I want to fix this problem & have a nice running vehicle for many years to come, but we are kind of baffled by the backfire issue. I also want to get the performance back to where it was & since I’ve got to change out the rockers, I am thinking why not go ahead and get lope I want from a mild cam as well. What I don’t know is what combo cam and roller rockers can be used with minimal changes to other parts already in the vehicle. Also, is there anything I should be concerned about the parts currently installed (i.e. 600cfm carb, MSD Distributor, etc…)

Suggestions? Opinions? Good Jokes?

 

I'd take him to small claims court. Take a witness and let the judge decide

 

was the engine run in for proper break in?

at this point without a blueprint/build sheet it becomes a mystery motor.

You could empirically address it by running a leakdown test in all cycls and determining the percent of leakdown, far better than running it to try and simply get compression readings.

I've been burned on engine 'rebuilds' before, they were for other makes, lets just say aircooled engine.

the shop didn't seem to say anything about headwork, as in a true valve job?

does it blow oil? Reason I ask is your rust comment, if the machine work was done, then he let it sit improperly with fresh pistons and rings, it sounds like the ring seating would be kissed bye-bye and you'd get lots of crankcase pressure, not so sure how AMCs act, the aircooleds made it obvious. A leakdown test would reveal this, can can be done insitu, just be careful you dont propel each piston WITH the compressed air applied during the procedure. You can tell alot from this, ring seating, valves, sticking, and maybe catch a misdegreed cam even.

I wanted to sue the guy who took my 1800$ back then and gave me a crap engine. But getting the empirical data from another unbiased professional source other than me, the developing the cost of damages, time, etc, I figured it wasn't worth it, plus he 'offered' to make it right if I made the four hour trip with it back to his shadyness, and I was concerned that effort would 'count' in court. I was probably wrong on multiple accounts................. Your mileage may vary legally, and probably does.

I am very sorry to hear of this and there is nothing more frustrating that waiting a super long time on an engine and then getting hosed, all we can do it pick up by the bootstraps and figure out how they screwed up and how to effectively fix it. IF you get them to pay for it too, great.

I also can't tell from your post if the negligence is implied to stand with the machine shop or the R&R shop, as in who did the actual engine machining and assembly work? I dont see how an R&R shop would know .40 over on pistons, unless they either got a short block shipped to them, or removed a head and measured. In that case I'd want to know my deck heights too and my head CC values to determine true compression ratio and variance per cyl.

 

That's terrible. Definately take him to small claims court.

In regards to the backfire, my 304 did the same thing....only once in a while and at speed, not at idle. After replacing just about everything and running for a while, the backfire came back.

As it turns out, it was with Prestolite Distributor (OEM '76) that was causing the problem. Even though we replaced the coil, ingnition module (x3), cap, rotor, wiring...it still backfired. Finally, I replaced the Prestolite with an HEI made for the 304. No special wires and kept the stock gapping on the plugs....wouldn't you know it?...the backfire has gone, finally.

 

I just got done swapping out my 304 for another 304. Running most likely the same intake and carb that you are. Had backfire issues. Took it into a mechanic who recommended me to some jeep gurus he knew. There is a special piece of equipment that is needed to properly time and set the choke on older vehicles. Most likely, this is your issue. As far as overheating, drill a small pilot hole in the thermostat. This will allow pressure to equalize across it and allow the thermostat to open. I had the same overheating problem at first and when a brand new thermostat was installed and the issue remained, I drilled it and haven't had the issue since. The new long block cost me $1300 after the core return.

 

I have a 73 cj5 same engine, same intake and carb. Had the same exact thing happening too. After consulting several mechanics and talking with others with the same set up, after ditching the edelbrock carb, my problem solved. If you want to keep that carb, make sure you change the springs and rods in it for it is set up to your altitude/location and engine size. I have a 1405 floating around that i had setup for the amc 304. It works but im always having to get it readjusted.
Some people love edels, others hate em. Myself, i just haven't had a great experience with them thus far but i wont rule them out completely.