Newly Rebuilt 351W keeps losing timing

[boblyon1]

I had my 351w rebuilt 2 months ago. This re-builder is extremely knowledgeable and sharp. I am running a straight Holly, no vacuum advance, with MSD 6AL ignition and an MSD distributor and coil. After about a 1000 miles of break-in, I took it in for timing and other adjustments. It had lately been popping in the 4500+rpm range, showing a few beats of dieseling on shut-off and occasionally backfiring, but not real loud. There had been a gradual decrease of power, most notably above 4000 rpm.

My re-builder was surprised that the timing was so far off. He re-set the timing and it ran well initially. Now (about 400 more miles) its doing the same thing and I suspect the timing is "slipping" again. The distributor is not loose at all, so I'm a little worried that there is some distributor gear wear. I DO NOT have a bronze distributor gear, it the standard steel one.

I searched the archives going back several years and can't find a problem associated with a 351W and distributor gearing. Any suggestions or ideas?

[CowtownCobra]

Either your coil is slowly dying or the distributor gear pin is sheared.

[cobras]

i could be wrong but wasnt there something about the dist hold down clamp being no good, something about it not properly holding down the dist, i think it was an alum piece of something, if anyone else has read something like this please chime in

[CHANMADD]

I have found that with these new Billet distributors the hold down clamp does not hold too tight. What you should do is once the timing is set just perfect,tighten the hold down and then use a punch and put a punch mark right at the join of the distributor and the block/manifold.
John

[tcrist]

You could also scribe a line on the base of the distributor and intake/block (an alignment mark so to say) after it is timed. That way when it starts to run funny you can just look at the alignment mark and see if the distributor has moved. If it has you can just move it back and look into changing or modifying the hold down clamp.

Edit: chanmadd, Are you thinking that would then hold the dist. from moving. Almost like pinning it?

Terry

[CHANMADD]

Yes exactly,it does'nt take much to keep it from moving.
John

[DAVID GAGNARD]

Originally Posted by tcrist

You could also scribe a line on the base of the distributor and intake/block (an alignment mark so to say) after it is timed. That way when it starts to run funny you can just look at the alignment mark and see if the distributor has moved. If it has you can just move it back and look into changing or modifying the hold down clamp.

Edit: chanmadd, Are you thinking that would then hold the dist. from moving. Almost like pinning it?

Terry

Zacctly what I did on my street car and race car, easy to do and easy to check, and it you have to pull it for some reason, you can always drop it right back in and be on the $$$$$$$$$$.....

David

[Jac Mac]

Several of the cast/chromed alloy clamps being sold by the 'dress up' kit suppliers have no real strength, & deform when tightened. Find the original steel version, paint it blue & fit it.

Check that the shaft is not running dry in the dist housing from lack of oil, this also can pull the dist housing in the retard direction in use. Mark the block/dizzy with a punch to have a quick reference to look at in the future.

[LMH]

Check the dist gear drive pin. Might be broken and the gear is slipping.
Larry

[Dwight]

oil filled coil that are installed on their side will burn up quickly.

Dwight

[CHANMADD]

My own car a billet distributor and ali intake turned a bit especially after a hard run.I punched it and no more problems.
John

[Rick Parker]

The design of the OEM distributor hold down clamp leaves a lot to be desired IMO. There are a select few available that put a hold down foot on each side of the distributor body. MSD makes a good one and a few of the aftermarket Mustang vendors do also, I think it's a cheap insurance policy.

http://www.msdignition.com/product.a...utor+hold+down

What would cause the distributor body to turn? There isn't any torque on it? (Is there?)

[PANAVIA]

I would pull the distributor and check the roll pin. we had a billet pertronix distributor shear a pin 1/2 way and drop timing,

[Jac Mac]

One problem that can cause the distributor body to turn in use is if the gear is fitted too low on the shaft--- this causes the thrust collar to bear against the dizzy housing when its clamped down and trys to make the whole dizzy turn with it. Easy to check if you have a spare empty 351w block to trial fit the dizzy in to ensure that you have some vertical clearance in the shaft between lower face of gear & block when fitted . Not a bad idea to do this every time you fit a new dizzy or replace a gear. I suspect that this is the ''real'' reason for some roll pin failures that are blamed on oil pumps etc.

[boblyon1]

A lot a great replies. I will have it back to the builder tomorrowmorning. Seems that there is some consensus that the hold down clamp might not be strong enough but I will also look at the possibility that the pin has sheared or that the gear is too far down on the shaft. I probably should have mentioned that the MSD coil is mounted vertically.

The rebuild was done because the distributor gearing on the cam was all chewed up. I had strongly suspected that a mechanic (I was traveling out of state) tried to install the wrong distributor (perhaps for a Cleveland 351??) but he claimed the damage was gradual. But I wonder.

Anyone have any other ideas?

[boblyon1]

I had a billet roller cam installed from Crower as part of te engine rebuild three months ago. At that time my builder checked and then double-checked with Crower who insisted we use a steel distributor gear. When we pulled the distributor the steel gear we found it was severely worn and abraded in places down to knife-edges, allowing the timing to slip. (the cam was harder steel and not worn at all) A third call to Crower resulted in the recommendation for a bronze distributor gear which we installed. Its running like a top now.

Although I've heard on this site that bronze distributor gears need replacing every 1000-2000 miles, my builder says that is not the case that they should give good wear. Anyone have comments on this? Thanks.

[Jac Mac]

It is not possible to install a dizzy with 351C gear into a 351W and run the motor ( The 351c gear is larger in dia & will not fit--short of using a large hammer & then it wont turn ).

Now you raise the possible issue of camshaft gear material & distributor gear material compatibility--- The camshaft ( metal its made from & who built it ) dictates which type of gear you must use on the distributor.

[vector1]

i just had problem on new build with dist. turning. the gear was too low on the shaft. with the dist. in hand there is a little up and down movement in the shaft, you want that same movement installed. if after installation you don't have this movement you're bottoming the gear in the block and your dist will turn and prob try to eat the dist.teeth.

[TButtrick]

I'm not sure I understand the builder's logic. I assume this is a roller motor. You've got a steel cam and a steel gear. You're builder says one steel gear (the cam) is harder than the other steel gear (the dizzy). The dizzy gear is the worn piece meaning that this steel is softer of the two steels. Now he wants to put on an even softer metal gear on the dizzy? Something isn't right. Hit your dizzy gear with a grinder. Does it spark? If it does, it's steel. If it doesn't, it's cast.

IMHO.. I'd throw out all that MSD crap and get a Pertronix.