Timing issue

[Coltrane]

Hey everyone! I'm having an issue with my motor and hoping some of you have some insight/experience with this. Here's a little backstory so you know what's going on (sorry it's a bit long...I just want you get the full story):

Motor is a 355 sbc with AFR heads and a custom comp cam, and I just brought it to the dyno shop last week. Made 3 pulls and good power - no issues there. Drove it home, got on it twice, and everything seemed fine.

Yesterday when I took it out, when I first stood on the throttle the motor coughed and almost shut off, then when I left off it idled and ran fine - cruising and part throttle was totally fine. I did it again and the same thing happened.

So I took it home and was thinking possibly a fuel issue, or maybe a plug wire issue, but all seemed okay. Then I checked the timing...I have been running 35-ish degrees locked out (MSD pro billet distributor, 6AL box, etc.) since the motor was put in 2 months ago, and when I checked it was LOW...like around 25 degrees. I checked the distributor and it was TIGHT - I couldn't turn it by hand no matter what. So I loosened the bolt, turned it, checked, and back to 35. Took it back out and it ran FINE.

After doing 2-3 more pulls, I put it away. Took it out again later that night...and it coughed and backfired again. Checked the timing...LOW.

My question is: what could be causing this? The distributor is not moving - it is clamped down TIGHT. Could it be the timing chain? Wrong/bad distributor gear (it's an iron gear that comes with the pro billet)?

Any help would be greatly appreciated!

 

[Ernest]

I say pull the distributor out, remove the cap, hold the cam gear tight in your hand and try to rotate the rotor with your other hand... something is shifting that shouldnt be, check the lockout device as well.

 

[jcelk]

i had a roll pin on the cam gear shear off once while adjusting the carb had me scratching my head

 

[Coltrane]

Appreciate the advice!

 

[Sweet_Johnny]

Considering what's already been mentioned I'd suspect the reluctor wheel being loose.

 

[bracketchev1221]

Is this the old style box or a programmable digital one?

 

[Coltrane]

Is this the old style box or a programmable digital one?

Old style

Also, I talked to Bill at Second Street Speed (who dyno tuned the car) and he thinks it's the iron distributor gear (since it's not a steel one) - I'll be checking that later today!

 

[Coltrane]

First off, with the distributor still tight and the cap off, I could move the rotor back and forth about a half inch or so. Took it out, held the gear, and the rotor wouldn't move at all. Also everything seemed tight and not moving. The gear does look worn in spots - think this could be the culprit? I didn't even think of getting the melonized gear when buying the distributor (yes the motor is a hydraulic roller). Might go ahead and order the new gear tonight.

 

[Ernest]

Hard to see, but those teeth look excessily worn... definately get a melanized gear in there and be to sure to coat it thoroughly with with break-in lube first before putting it back in the engine.

From all the features listed on HOLLEY's website, no mention of a melanized gear, all that cheddar they charge for it.

When ordering a new gear, first find out if your msd destributor shaft is either .491" or .500" in width.

EDIT: according to the list of features on SUMMIT's website, it has an iron gear.

 

[Coltrane]

Hard to see, but those teeth look excessily worn... definately get a melanized gear in there and be to sure to coat it thoroughly with with break-in lube first before putting it back in the engine.

From all the features listed on HOLLEY's website, no mention of a melanized gear, all that cheddar they charge for it.

When ordering a new gear, first find out if your msd destributor shaft is either .491" or .500" in width.

EDIT: according to the list of features on SUMMIT's website, it has an iron gear.

Thanks for that! I'll change the oil Friday when I'm somewhat free just to see how much metal is in there...the silver-looking wear on the teeth looks worse in the photos than in person (the light bouncing off makes it seem even worse), but yes I agree it's worn down!