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

Old 04-11-2004, 02:38 AM
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***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)

As always, thanks in advance for everybody's wisdom and time.
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Old 04-11-2004, 07:06 AM
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Originally posted by blue thunder
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

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
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Old 04-11-2004, 07:33 AM
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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
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Old 04-11-2004, 09:24 AM
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I have a compression gauge.

What will I be looking for, a low pressure cylinder while cranking?
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Old 04-11-2004, 10:38 AM
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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
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Old 04-11-2004, 11:45 AM
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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
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Old 04-11-2004, 12:11 PM
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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
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Old 04-11-2004, 01:27 PM
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Originally posted by blue thunder
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
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.
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Old 04-11-2004, 01:33 PM
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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!
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Old 04-11-2004, 05:59 PM
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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.
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