I've had an annoying knock since installing the new 396. I've been assuming it was a lifter. The sound seems to be coming from the lifter galley in the area of the 6 or 8 cylinder.

I read a thread from Dr. Huxtable regarding his distributor. I think WW7 mentioned that a new distributor from DUI needed to be checked for end play at the gear. Well I was starting to remove my intake to find a bad lifter. I pulled the distributor I got from DUI. I checked the end play and found .026" of play.

Since the distributor gear and #8 lifters are very close to each other, I'm wondering if the knock is actually from too much play in the gear. Anyone ever experienced this? I hate to pull this Super Ram intake if I don't have to.

 

End play will not result in a knock sound. It may cause variation in timing but no noise. Sorry. Double check your lifter preload. Check for contact of the rocker arms on the inside of the valve covers. (been there).

 

Dang, that would have been so easy. I've already ground away all the interferences on the valve covers. I'll check the valve adjustment but I have to believe Jim Barth got that right. I'm guessing the intake is coming off.

 

Hey Craig, back before with my old motor one of my rockers was tapping up against my valve cover breather. Was causing the ticking noise.

You could also always just pull the covers and crank it for a sec before doing anything else to listen for the noise to see if it goes away. might be a good process of elimination. I'm sure jim set it right, mine is silent, maybe something came loose

 

Hey Craig, sorry to hear there is a noise there. I think it's either the rocker hitting the valve covers. Or I guess it's possible to have a bad lifter, even though those are brand new GM lifters. I doubt the rockers are adjusted wrong. It's not the distributor as Willie mentioned. If there is anything I can do, let me know.

 

Thanks Jim. I was just hoping for something simple. But now that I know the gear needs shimming, I may as well take care of that too.

 

It still might be something super simple. Preload on one might be a hair loose (as mentioned above), exhaust leak, or even a super loud fuel injector. Take you time going over it - you'll find it.

 

Craig, I used to use a piece of tubing to isolate odd sounds in a motor. It's similar to using a wood dowel, but a lot more directional and fits into tight places a bit easier. HTH

 

A mechanic's stethoscope is a very handy tool and only $4 at Harbor Freight:

http://www.harborfreight.com/mechani...ope-41966.html

Check is out.

 

I solved the knock mystery. I shimmed the excess end play out of the distributor gear. The play was .028" and I got it to .008". That alone eliminated most of the knocking sound. Then I checked the valve cover for signs of interference. I had ground a lot of metal off already, but there was one spot that was still making contact. So I ground the crap out of it again. The engine is now much quieter. I'll probably pull the other cover to make sure there's no contact there. But I'm happy to report the intake will not be coming off.

I think the engine was suffering from some spark scatter. It seems to idle more steady than before.

 

Craig,
Glad to hear you got this resolved without having to tear the motor apart.. I just bought a new DUI distributor a few weeks ago and it had an unbelievable .037 end play. Im sure there are alot of guys that have excessive end play in there distributors right now and don't even know it, and like you found out, it can cause spark scatter, noise, and also excessive wear on the gears.......WW

 

Actually, all this fuss about distributor endplay is about nothing. The cam turns one direction and so does the distributor. The direction of rotation forces the distributor shaft down so theoreticially, it doesn't move up and change the timing. I have never shimmed my original 84 distributor but I know it has some healthy endplay. I never thought anything about it and I still don't. Willie

 

Whatever You Do,

DO NOT SHIM AN HEI DISTRIBUTOR DRIVEN GEAR END PLAY DOWN TO .006" inches as recommended in some old 20 + year old magazine tech articles.

Been there & done that.

The cast HEI aluminum housing GROWS in length with built up engine heat soak.

They also can fail suddenly with 80 to 100 psi running oil pressure & 20w50 or straight 40 weight racing oil.
Cast housing likely will crack in middle or up on top where distributor base meets.

.010" to .015" is where I like to set HEI gear end play to with MOROSO distributor shims.
Need the kit for a .491" diameter shaft.

Spark scatter(seemingly high distributor drive end gear play clearance) may be a problem for the Road Race guys here on C4.
On & off the gas pedal very often & at a very rapid pace.

On the street or drag race not likely a very big issue.

Less than .010 " HEI gear end play,
No lubricating engine oil can get in properly when the distributor aluminum housing grows with engine heat.
It expands that much with heat.
It will burn up the distributor drive gear & HOUSING & SHIM(S).
Lost a race that way dirt tracking.
My guy was in the lead on the final lap & last turn before the checkered WIN flag dropped.
Engine quit suddenly & he got passed with ease.

I hate HEI's for circle track racing.
Blown up distributor rotors are a common problem at 8,500+ RPM's & drag racing too.

Vertex Magnetos best there.
I love them & rebuild them.
1 going in the 87 with my 410 sbc.

Davis Unified Ignitions(DUI) knows what they are doing.
leave well enough alone.
.037" end play is OK & safe on the street .
Tell them you are racing & they will build you a distributor to meet your needs.

BR