Timing problems - Help before I take a sledge to the motor!
 

Here’s the dealio.

1995 Gen V 454 Carb Mag, all stock except Edelbrock Performer intake, Lightning headers.
Before I installed my new cam (Comp Cams XR268 per Dennis Moore's suggestion) we cranked the motor to TDC, two dots on timing gears lined up.
Installed the cam.
Set dist rotor facing #1 after having again made sure TDC via finger in #1 hole.
Ran it through a 20 minute break in.
After break in, had some idling problems, so I started messing with the idle mixture screws before I realized it was a linkage problem (Carter AFB 750).
Took it to the water and it wouldn’t open up, back fired a couple of times and tach was going nutty. An hour later we realized I had the distributor bolt upside down and that was allowing the dist to move. Corrected that, messed with the straight idle screw and started sounding good.
Made one pass, running strong, but forgot the damn GPS in the truck! :mad:
Returned to pick up the GPS and after idling out, hear a tapping noise. After scratching heads we smell exhaust and realize we have a manifold exhaust leak.
Torqued down the manifold bolts, let it sit all night and tightened again in the morning. Cranked the motor and problem solved.
Changed out old spark plugs to new merc spec plugs (Champion RV15YC4), had trouble getting the #5 in due to the headers.
Returned to the lake, fired right up and sounded good.
Went to hit it and got a cracking noise coming from the carb, idle is fine, but under load, cracking. The more throttle, the more it cracks.
Limped to a safe spot and verified correct plug on rotor position. Again found TDC and verified rotor facing #1 cylinder. Triple checked correct wire to plug locations. Moved timing forward and back, it doesn’t seem to matter, still spitting/cracking.
Limped back home and said fuggit!

Any thoughts?
This is a cracking/spitting noise coming from the carb under load.

What is your initial timing?

Rember to get true timming readings on a 1995 TB V distributor you need to ground the purple / white tracer wire that comes off the distrib. plug. Rag's

Did you replace the timing chain and sprocket set with the new cam? If so, did the crank cam have three keyways to chose from depending on desired cam timing?

BT :cool:

It ran good then puked...I think he jumped timing.

Sounds like it could have wiped out a cam lobe.

Hold the phone.

I know this true for SBCs and I believe it is true for all GM V-style engines. When the the dots are aligned at crank at 12:00, cam at 6:00, #6 is at TDC on compression, NOT #1.

#1 is on TDC compression when the dots are at crank 12:00, and cam 12:00. You're 180* off.

Not unless he stuck his finger in #6 hole.

Ah, read too fast. My bad.

New Cap? A carbon track in the Dist. cap can really piss you off!

I'm looking at cam lobe, didn't mention anything about cam breakin.

I agree with Dyno. After all ther jerking around and handling with the distributor, make sure the cap and rotor is is good condition. Check and make sure your plug wires are not arcing out on the Lightings. In other words, do the easy stuff first before you panic.

I agree with Dyno. After all ther jerking around and handling with the distributor, make sure the cap and rotor is is good condition. Check and make sure your plug wires are not arcing out on the Lightings. In other words, do the easy stuff first before you panic.

Many many moons ago I rebuilt a little in-line 4 popper. Couldn't get the bastard to run right to save my ass. Finally got pissed and had a tow truck come and get it to take it to a real mechanic to fix it. An hour later they called and said she was purring like a kittem. WTF!! Yep, greasy hand print on the rotor caused all my trouble.

BT :cool:

Ben there done that!!

Thanks for the input guys. To answer a couple of quick questions;

Initial timing set at 8-12, it didn't matter, would crack throughout.
The cam was broke in properly, 20+ min at 2500-3000, overfilled oil, cam grease and assembly lube.

I'm also thinking it's something stupid, I suspect something is up with the cap and rotor by now. I haven't had a chance to wrench, but am curious to verify firing order and make sure no arching. On the lake I had several gear heads helping (looked like a damn poker game around my motor), but some of these guys were a *little buzzed*. I didn't have any manuals with me so I had to rely upon their beer goggle advice.

I'll also check the oil filter to see if metal is in it from a wasted cam lobe.

Thanks guys. I'll post an update, no matter how stupid the problem was.

1. I would check to make sure that 5 and 7 are not
crossed or any other plugs for that matter, 18436572.
2. Verify that all the exhaust ro,ckers are moving
equally, by taking plugs out and rolling motor over
with the
starter.
3. Make sure you don't have an exhaust rocker too
tight, that would cause the popping.

As ragtop mentioned, did you ground the purple wire?:confused:

I think it would be a intake rocker.If it were too tight not allowing the in. valve to close would cause popping through intake.BOB

Could an intake rocker be a problem that showed up after the motor had already ran fine for at least a few passes?

My guess is it could?

I'll add this to my list of things to check before the sledge comes out! :eek: :eek:

CHECK TO SEE WHAT A VACUUM GAUGE READS, ALSO CHECK IGNITION TIMING 18436572. TOM

Sounds like a cam lobe is gone!!

600HPs...this ain't no Saab Son!!!;)

I'm gonna start wrenching tomorrow so I'll let you guys know.

Thanks again for all the help and stay tuned.....

HEY R, I THINK YOUR CORRECT! IF HE CHECKS VACUUM, THEN THAT WILL TELL IF THERE IS A WIPED LOBE. TOM P.S. I HOPE ITS JUST A CROSSED WIRE!

my money is on a cracked plug or crossed wire. was running good untill changed plugs.

later

I'm stickin' with a wiped lobe....It ran fine for a short time....then it started popping thru carb....possibly tightened a rocker to tight. Have heard of this before.

But for your sake I hope it is just a bad wire, plug or crossed wire.:)

I'm not familiar with a vacuum gauge, how do you do it?

How else do you check for a wiped cam lobe? I thought you checked the oil filter to see if there is metal in it from the lobe?

What happens if it is a lobe? Full rebuild?

You guys are scaring me now!

carb.
 

Get rid of that carter, go with holley at least you have a starting point .Make sure you have a good coil.

Craig,
go with the basics first. If you did wipe a cam lobe the metal will end up on the piston skirts, so a tear down would be in order.
You hook the vaccum gauge to the intake manifold and watch it.. if it bounces around then valve problems..possibly a cam lobe.
Do a search on the net for vacumm gauge info. There is way to read them. But at idle it may bounce some, then when off idle it should increase and stay steady. But look at ignition first. If you have a plug wire crossed it will pop back thru the carb.

Take it one step at a time, remember basics, dont panic till you have to. Do a compression test or a leakdown test. Remove the valve covers and bump the motor over, check each rocker for a loose one. If an ex valve isnt opening.. it can blow back thru the intake.
Roll the motor over and see if all the rockers are moving the same amount. If you suspect one, use a dial indicator to measure the valve lift.

Good luck and be patient, this is a time to learn and most of us have been here and done it..

Dick

I sincerely hope it is a bad wire or something like that, but the scary thing is that it pops regardless of ignition timing. A backed off rocker adjustment or a bad exhaust lobe forces exhaust to exit during the following intake stroke, firing off the intake charge. Being a new cam I would definitely check it out carefully before running the engine again. The more it is run with 'Gltter oil', the more damage done to EVERYTHING.

I had a 454 with a new Erson cam that was in the engine when I bought it. When it had a couple of hours of run-in time, it burped under load. I noticed none of the lifters/pushrods were rotating- a sure sign of trouble on a flat tappet cam. I don't think the lobes where machined right. POS cam lost one lobe with 2 others in early failure mode. Isky never failed me before or since...

***Update***

I was able to wrench a little today and here is where I’m at;

I started by cutting open the oil filter and inspecting the filer – no evidence of any glitter or silver residue.

I then changed out all the new plugs to the old ones; verified wire positions/painstakingly made sure no wires touching or arching on anything.

Fired it and it does the same thing – cracking at 2500 rpm, fine at idle (in fact sounds great, good idle at 750). Again checked the oil for any silver sheen, none.

And BTW, the rocker arms are non-adjustable (also installed new hydraulic lifters that came with cam) and torqued rockers to 44 ft lbs per specs. The manual says “No additional adjustment of the valves is necessary as the lash is set automatically when the rocker is tightened to specifications.”

-----------------------------

When the cam was installed the cam gear was at 6, the crankshaft at 12, we then set rotor to #1/stabbed the dist. Now I think we should have cranked it another 360 so the balancer mark should line up at TDC, not sure if that was done?

I looked at a digital photo of my dist position before the cam install and it was facing straight with the two sensor wires also centered/facing straight. Now the dist is sitting to the left (2,4,6,8) side at least 3/8 to 1/2 inch off the original position.

Could it be that I am something less than 180 off, but still way off on the timing? Or 180 off and advanced so far the damn thing runs? The motor does start and idles fine, and we got in one high-speed pass.

Can a lobe be wiped in as little as 45 minutes?

This stuff is starting to make my head hurt!!!

I’m thinking I’ll have to take it to the shop since I am running out of time. I would prefer to do the work myself (it’s fun and learning lots), but seeing my neighbor heading out every weekend is getting to me, especially since the boat has been turnkey for the past eight seasons (until now) :mad: :mad:

As always, thanks in advance for everybody's wisdom and time. :)

I'll revert to my prior question. The reason I asked this is the crank sprocket (on some timing set) have 3 ways you can set them up. If your cam is advanced or retarded too much you may have run out of valve to piston clearance and bent an intake valve during your one high speed pass. This would show up on a leak test, compression test or vacuum test. It would also be evident by a valve tap at idle.

BT :cool:

Lot of good advice here. The best of which is stay calm and work methodically.

1. First establish timing references: At this point unless you open the timing cover you need to assume the marks were lined up on the gears properly a) set crankshaft on TDC watching the rocker arms to make sure that you pickup the right stroke (i.e. TDC mark after the intake valve closes)

2. Reinstall distributor noting position of rotor in relation to the cap wire position. It should be relatively close to your digital pic from before this all started.

3. Carefully install plug wires matching firing order and rotation of the distributor.

4. Do a compression check now !!!! It will ease your mind with respect to the following possible causes. a. bad lifter, b. misplaced push rod - do the intake and exhaust come in different lengths. c. a tuliped valve d. a carboned up seat

If it truly made a good pass then the problem started I would be looking for damage. It should show in the compression or leakdown test. Did you match carb fuel flow to the new cam? Did it run lean and cause damage?

Start it up on a hose at night and watch for arcing off the wires.

Take the cap and upside down pour in a cup of alcohol and let it set for a few minutes to see if any leaks out to check for cracks.

SLOW AND METHODICAL RECORD RESULTS EACH STEP

I have a compression gauge.

What will I be looking for, a low pressure cylinder while cranking?

equal pressure from cylinder to cylinder. if most of your cylinders or at say 150 and one of them is at 90 then thats the cylinder with the problem.

later

Ok, I'd throw out the non adj. valve train for anything other than stock , Just my opinion. I did this on my first gen 5, 6 years ago. Arp makes special rocker studs with the 3/8 thread, and you then would make sure to have guideplates that go with them and the pushrods you will use. Then mk4 valvetrain would work. I did this because the block and heads were decked. Motor had a steam burnt path between 2 cyls. I even saved the head by welding it. I like to be able set my valve lash with the motor running. You could have a burnt valve also. Sure, the bolts could have shims put under them if motor was machined. GM did this to speed up production and reduce costs, not to build a better motor, at that time they didn't even care if it would end up in a boat. BBB

I have never heard of a non-adjustable valve train even with hydraulic lifters. It sounds to me like you have an intake rocker set too tight. I know that on a hydraulic valve train when you adjust a rocker down while the engine is running you will hear a momentary "cracking" out of the carb. If you're 110% sure you have quality plug wires and they're not crossed then I would look at valve train. Hook a vacuum gauge up to it and tell us what it does when it pops.

Roby

Same stock sprocket, only one way to attach the cam to it. The cam kit did not come with any shims, so I believe it is made to be installed "straight up"?

Next order of business...compression check. Then starting over from square one, resetting dist on TDC etc. If the timing cover wasn't such a pain in the ass to reinstall, I'd pop that off too, but man, it was a mutha getting it back on.

I'm also starting to wonder if I got the wrong cam in there with all the remaining stock valve train parts.

Moore suggested a Comp Cams 268, but inhis book he recommends a 256, not sure of this is a factor or not.

Compression check, and check to see operation of valve train components, or if they have been damaged before I start over is what I meant to type!

I would double (triple) check the distributor.

If you stab it at TDC you will have to crank the distributor around to the correct timing. Be off center.

Put the engine to 32 degrees before TDC on #1 compression stroke and stab it there. That way it will be square when timing is set.

And yes you can kill a cam lobe in a matter of a few minutes. Exhasut lobe going down will pop out the carb under load. Still pressure in the cylinder when the intake valve opens.

I am not familiar with the non adjustables. Cannot help there.