I need to swap to a small cap distributor. For the moment it's going in my 86 LB9 flat tappet engine. Soon that will be replaced with a Vortec 350 running a Comp 276HR.

The small cap distributor is new. I assume it has a Mellonized gear.

Do I need to swap it for running in the LB9? Then swap it back for the Vortec?

GD

 

The treated gear will work fine on either cam type.

 

That's the real question. Is it a melonized gear? I purchased a cheapo HEI replacement and I doubt it has anything special as a gear other than good old chinesium.
I suppose another question might be what is the cam made of? That's the issue isn't it? OEM are all cast correct? My Comp 276 was also cast and no special gear was required (as per Comp tech support 10 years ago and tens of thousands of miles of use) .

 

This is a $200 distributor from Davis Unified Ignition (performancedistributors.com) and per the southern gentleman I spoke with on the phone this morning it has a Mellonized gear. He agrees with Sofa's assessment that the treated gear will be fine on the old LB9 cam and should not require changing unless I see excessive wear when I move to the Vortec. As with anything though I will take all opinions into consideration on the matter. It's looking like I won't need to worry about it though.

GD

 

Out of curiosity, I'd like to know what material your 276 is. At first thought (when I purchased mine) being a roller cam (albeit hydraulic) I had the thinking that it might require a special distributor gear. My understanding now is that solid rollers are generally billet while that particular hydraulic roller is not.
While on the subject of Davis Unified Ignition, did you opt for a custom advance curve built in? At one time I had heard they had an excellent reputation for getting it right based on the particular engine specs. Right down to the vacuum advance timing. Which by the way I found particularly time consuming to nail down.

 

This is the computer controlled small cap so it has no built in advance - that's all in the TPI computer. I got it from A-Tech motorsports, which is Summit Racing's wholesale division so I got it a few bucks cheaper than the normal $199 retail. Being computer controlled I can just use the off-the-shelf model and not have to wait for them to custom build/curve it.

That's what I have heard also - that the solid roller cams are billet and require a bronze or composite gear. And the "Mellonized" is just a coating and it is slightly harder than a non coated gear but in practice apparently they are interchangeable with hydraulic flat tappet and hydraulic roller even though GM only used Mellonized gears with roller cams from the factory. There is some confusion surrounding the 85 and 86 large cap computer controlled distributor gears - I don't know if they were coated or not. That distributor was used for both the flat tappet TPI engines for 85 and 86, and then also on the 87+ L98 corvette so...... not really sure.

GD

 

Solid roller cams are usually made of much harder material than hyd rollers or flat tappet. They need a soft, somewhat self-lubricating material for the gear. Bronze was the universal solution for them until relatively recently.

AFAIK there is no non-computer "small-cap" dist available from GM. Might be possible to build an aftermarket one but all vehicles that it came in, AFAIK, were computer-controlled. At least in the US. There might be exceptions in export product that I don't know about though.

FYI GD, I knew the founder of Performance Distributors, back in the 70s... he started out working at the AC/Delco W/D in Memphis, got hold of an old dist spinner-upper machine (a Sun I think it was... I can see it in my mind's eye but I'm too optically challenged anymore to read the label...) and set it up in his garage, and started building distributors for racers on the side. That evolved into PD. He passed away some years ago unfortunately and his son took over PD. I miss him, he was a good friend back then, and KNEW how to make a distributor curve that matched what an engine wanted.

 

That's neat that you knew the founder. They seem like good people making a quality product. Not many shops you can call and speak with in english anymore. All the posts I've seen about ignition module failure... I didn't want to enter that downward spiral so I opted for their complete distributor and matched coil. They told me to run a .060 gap.

GD

 

I have a comp cams poly gear on my solid roller small cap distributor, had to make a small tube like shim because the small cap and large cap distributors have different size shafts.

 

The small cap computer controlled distributors don't use the same gear as the large cap. The shaft is a smaller diameter. If you had a special gear on the large cap, it won't fit on the small one.

OEM gears will work on most oem style camshafts. You only need a bronze gear when using billet camshafts.

 

I found this for you. Hope it helps. https://www.thirdgen.org/forums/tech...ml#post6282517

 

I can't see through your mind's eye, and I'd probably be frightened if I could, but I believe you are describing the old slant-top Sun distributor setup machine. Almost every speed shop had one, and almost no speed shop had anyone who really knew how to use it.

 

Looks like this I bet.



An old and ancient Sun 500. One of my favourite tools back in the day. And even today if I still had easy access to it.

And something from DUI that some of you may find interesting. An article written by Steve Davis (Performance Distributors founder Kelly Davis' son) with an introduction by David Vizard. Info I've used over the years to build ignition curves for my projects.
https://fordsix.com/archive/www.clas...SparkTech.html

 

I saw this on Comp's web site when I was looking for information.... I don't entirely trust Comp after buying one of their complete cam kits and finding out it included basically none of the right parts.

That information suggests that I can't use the Mellonized gear on the older LB9 cam..... and really seems to be surreptitiously steering everyone to buy their composite gear for like $100 by obfuscating the whole situation. I see many reports of those breaking so I'm not at all sold on that idea... and other than being lighter and maybe lasting longer on a billet cam than bronze I'm not seeing the benefit to using this technology on a stock style HR cam.

GD

 

Swap Complete. If anyone is looking for a working large cap distributor hit me up. Needs a cap and rotor but gear is in excellent condition, shaft is tight, etc. Swapped due to suspected cause of somewhat random audible pinging (probably the cap and rotor upon inspection) and since the upcoming First Performance Intake will create fitment issues with a large cap that I would rather not fight.

Pics of the cap, rotor, and gear. 170k on this distributor gear - virtually no wear to be seen. Love that GM engineering.

https://photos.app.goo.gl/XhAy6TWYLSj5oNvT8

Incidentally these are AC-Delco cap and rotor IIRC. And they certainly have less than 5,000 miles on them. Pretty disappointed in the quality.

Maybe someone can tell if this is Mellonized or not. It's the 86 large cap so last year for the large cap on the F body and last year before hydraulic roller - but still a one-piece rear main.

The Davis Unified Ignition distributor and matching Screamin Demon coil worked perfectly with no drama. Excellent build quality - polished billet distributor body, all brass cap and rotor elements. Very nice quality parts by all appearances. Highly recommended.

GD