Timing Question??

[TOPTRUCKBOB]

I have a comp cam in my wifes 360 (456 lift) with roller rockers. I have it apart for some dist and cam gear problems.When it was running I noticed i coulden't get it to run worth a crap when i set the timing at factory settings. I tried to advance it and seemed to run much beter at about 20 degrees BTDC but skipped at rpms over 4000. Should I consider advancing or retarding the valve timing?? Or should I expect it to run well at near factory settings? BOB

[tufcj]

When you set the timing, the vacuum advance hose should be disconnected and plugged. Make sure your vacuum and mechanical advances are both working and move without sticking. I'd say you're looking for trouble with the initial timing at more than 10-12 degrees.

You might also check to see that the timing mark on the harmonic is truly at TDC. I've seen the outer ring on the harmonic slip if the rubber has deteriorated.

20 degrees sounds like way too much initial advance, which is why it's missing when full advance (centrifugal and vacuum) is pulling in at higher RPM.

Bob
tufcj

[TOPTRUCKBOB]

Bob, I am useing a brand new DUI dist and have checked it out and everything is good. The harmo balancer seems in good shape also. But as to my valve timing question...Any thoughts about retarding or advanceing a tooth.. ? I am new at this AMC thing and am not sure with the cam if I should consider this. Thanks for the help, Bob k

[tufcj]

It should run fine with cam timing at the factory setting. I ran a Crane cam in my Jeep advanced 4 degrees, and had a problem with carbon buildup on the valves. Returned it to 0, and no more problem. You need a timing set with multiple keyways in the small gear. Just advancing or retarding a tooth is WAY too much (over 10 degrees). Advancing the cam will give more low end torque, but sacrifice top end HP. Retarding the cam loses low end, but gains top end HP. Straight up factory is a happy medium. What you do depends on how you use the vehicle.

Cam timing and spark timing are independent of each other. Changing cam timing changes where the valves open in relationship to the piston position.

I'm curious which heads you're using with roller rockers, and what brand rollers you're using. Heads that had bridged rockers generally require some machining of the pedestal bases, and the use of guide plates. Even on my 69 390 that had factory studs (1970 heads), I had to install .100" longer pushrods to get the rocker geometry right with roller rockers (Crane gold).

I'm probably creating more questions than I'm answering, but I need all the facts to give a correct answer.

Bob
tufcj

[TOPTRUCKBOB]

Bob, Thanks for the info. The jeep belongs to my wife and is used around town but also to run the trails at tellico. It is built with alot of other than stock parts. Dana 44 rear with disk brakes a electric line lock and a spool ( scout). D44 front with a detroit locker and warn high strength axles.(wagoneer) np208 behind a 727 from a j20 jeep truck.8" of lift. SS 36x14.50x15 radials on Trail ready beadlocks.Full interior cage,8000i warn up front 3 point raceing harness buckets..etc..etc..etc. Ant then the engine. A 1974 360, 60 over stock heads (I had 275 thousandths cut from the pedastools and drilled and tapped for chevy style 3/8 studs.) ported and the rollers are from comp and are a standard 1.6 ratio After I bought a push rod length checker and went through that whole process I ended up buying a set of stock length hardend push rods, afterward i ran across a set of stock style heads with the studs(dosent it always work that way,and the guy GAVE them to me) after some measureing I realized the setup I had with the pushrod guideplates and all I was almost exactly the same as the stock stud style heads,so if I had the stud style heads first I could have avoided all that machineing and pushrod length checking etc..etc..etc.. I could have used my new cam and just installed the roller rockers and used the stock pushrods!!! and the cam is also comp 456 lift on exaust and intake, also I am running the edlebrock shorty headers into dual flowmasters and a edlebrock performer alum intake with a holly 670 truck avenger carb and a DUI distributor.Doubble roller timimg chain set (the rebuild guy supplied it and I don't know what brand it is.) I have checked everything else out and have just ordered the dist and cam gearsets here and an oil punp kit with priming tool. I have spent alot of thim and $$$$$ on this engine and the jeep and plan to fix it once and for all ! (otherwise I will take a sledge hammer the the whole engine and start over with a SBC) Well you asked for it!  Thanks, Bob :shock: :shock:

[tufcj]

Sounds like a nice setup rig. I'm running an Edelbrock Performer in my CJ. It's only like .448 and .472 lifts. 1974 360, bone stock bottom end, 1970 291C casting heads that have been polished/ported/gasket matched. Crane gold roller rockers. It's got a performer manifold with Howell EFI. Ignition is a Mallory Unilite. It's been a great combo. Dependable, with plenty of torque and HP.

As far as yours, I'd back initial timing down to 10 degrees (advance disconnected), even if you have to bump the idle up a bit. Make sure the advance is plugged into a ported vacuum source. That's one with NO vacuum at idle, and increases as the throttle is opened. It's usually about midway up the side of the carb somewhere. Manifold vacuum is nearly opposite, and messes up total timing.

While your timing cover is off, check the timing marks, make sure they're right. Most roller sets have at least 3 keyways in the small gear. They're usually marked with an A (advanced), 0, and R (retarded).

Any other questions, just ask.

Bob
tufcj

[bradbeyer]

Was this issue ever resolved? I am having the same sort of problem.

I have done a rebuild on my 360 and the timing is advanced almost 40 degrees. Has anyone had this problem?

Here is what is in the engine new:
crank
cam (RV)
Piston & rings (30 over)
lifters
valve job done to heads
oil pump
water pump
alternator
power steering pump
timing chain and gears
cam gear
distributor and distributor gear
I did the valley oil pump mod
intake with TBI setup (all new sensors and computer)
MSD ignition and coil

I am at a lost with why my engine is so far advanced. When driving around town it gets "loaded" (carbon) up and will cut out a couple of time if you try to get on it (I figured due to the advanced timing). Once you stay in it it runs fine. Any help is greatly appreciated.

Brad

[FUBAR]

any HEI distributor will require a great deal of advance in the timing. you should also gap your plugs to .055