When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Tech / General EngineIs your car making a strange sound or won't start? Thinking of adding power with a new combination? Need other technical information or engine specific advice? Don't see another board for your problem? Post it here!
Hi guys,
been trawling the forums looking for some specifics on this and found a couple of threads however nothing specific to the experimental era of 1987. I have an 87 camaro with the dreaded lg4. Lookin to ditch the cc dist and carb, ive got another quadrajet to put on just need a distributor. apart from the electrical pigtails which is easily rectified, would pretty much any vac advance distributor for the 82-86 305/350 sbc work?, or is there something different about it? ie the gear on the bottom etc?
These things are difficult to get parts for here in 'Straya (shipping etc) and ive gone through a few icm's etc.
would pretty much any vac advance distributor for the 82-86 305/350 sbc work?,
NO. "Big cap" distributors have a different sized gear compared to the "small cap " distributors. ( can't recall the sizes off the top of my head right now ! )
The roller cams are not made from the same material as the non-roller cams. You need to be sure that the distributor gear at the bottom of the distributor can handle the roller cam. IIRC a "melonized" gear ( or something like that) is needed to properly install a 'big cap' distributor on a roller cam.
I'm pretty sure that most new aftermarket distributors will use this kind of gear,....... but BE SURE to verify that when buying your new distributor / Distributor gear !
Sorry for the bump but ive been searching for the last 24 hours with multiple emails to different suppliers and am still unable to find one, does anyone have any advice or experience with this?
NO. "Big cap" distributors have a different sized gear compared to the "small cap " distributors. ( can't recall the sizes off the top of my head right now ! )
The roller cams are not made from the same material as the non-roller cams. You need to be sure that the distributor gear at the bottom of the distributor can handle the roller cam. IIRC a "melonized" gear ( or something like that) is needed to properly install a 'big cap' distributor on a roller cam.
I'm pretty sure that most new aftermarket distributors will use this kind of gear,....... but BE SURE to verify that when buying your new distributor / Distributor gear !
You had me scratching my head there for a second. I had to go through our collection of 20 or so SBC distributors to be sure. Every gear from a 67 breaker point unit up through the small cap HEI is the very same. The only way any dist gear could be a different size is if the cam was moved in the block or the cam gear was a different size.
As far as I know, all GM factory roller cams, for use in distributor ignition applications, use an iron dist drive gear. This allows use of a steel dist gear with the roller cam. Otherwise, we would be replacing the dist gears on high mileage engines, which we do in very rare cases. Dist gear material is a concern only on AM cams without iron dist drive gears. I can't imagine ever using a cam without an iron gear.
It is correct that any 76 up to about 85(any pre EST), or better yet, an MSD or DUI brand HEI distributor will drop right into your 87 and will work fine. I've installed a few of the Mallory units for customers looking for a cheaper option to the MSD or Davis Unified and they have been in service for years without issue. Mallory, like MSD, makes an HEI unit for just about every application.
I remember there were changes from the big-vs-small cap distributor gears:
MSD Ignition’s Erik Brock explained material differences,”Many OEM manufacturers used a cast iron gear from 1986 back. From 1986 forward, we saw a change to hydraulic roller cams in engines and steel distributor gears were being used. Many of the high performance guys are using billet race cams that require the use of a bronze gear. Mating the wrong distributor gear to the camshaft can cause huge problems and potentially involve rebuilding the engine.”
I built a 'mutt' engine years back ( 88 TBI block, 87 TPI cam, 416 heads, big cap distrib ) and seem to remember that the gear from small cap distrib was not the proper size and would not fit the big cap distributor. If my memory is right, than you will need to buy a replacement gear; just be sure the replacement gear is the right size and the right material for the cam it's getting used with. ( an aftermarket vac-advanced distributor will probably already have a hardened steel gear on it - check to be sure ! )
Just found this on a search: (Maybe I'm not )
The gear at the bottom of the small-cap HEI--'87 and newer pickup trucks, for example--are all melonized. They will not fit a big-cap distributor, the distributor shaft is tiny on the small-cap units.
The large-cap gears are NOT for the most part, so you need to buy the melonized one from GM.
"I guess" MSD sells the GM melonized gear as a "Marine Gear" (after honing it out to fit their .500 shaft) but I don't think they install it on any of their distributors unless you make special arrangements. Could be wrong here.
Cheers guys and once again thanks for the info. From what ASE Doc has said on this thread and from what Five7 said in another one that i just found, the stock gears are fine and dont need to be melonised for stock shafts unlike aftermarkets. ill let you know how i go.
All I know is that we had an old 69?? Chevy truck with the old 307. Had distributor problems so we pulled the old points distributor and dropped in an HEI unit I had sitting around. Put a cheap set of wires on it and ran 12v to it and ran it for awhile. Didn't have any issues.
So what am I missing. This thread seems to contradict a little bit. Im curious for 2 reasons. 1: Im fixing to pull the CC stuff off an 86 lg4 and swap in a large cap HEI, and 2: Im fixing to put a large cap HEI on a 67 396.
Want to make sure we all leave here on the right page.
I don't know about the iron gears. I see that there is an iron gear available. The flat tappet cams are nodular iron. I would be concerned about using an iron gear even on a nodular iron cam, for reasons of wear. GM has used steel gears for as long as I can remember. I'm pretty sure that all the dists I have on hand have steel gears on them. I'll talk to my buddy about it. He's more familiar with the early GM than I am. Steel dist gear is what you want for an iron cam gear.
Remember, dissimilar metals and all that. Steel is just slightly softer than iron and has a different grain so it will wear first. These gears still last the life of a vehicle.
The only way that one SBC distributor wouldn't fit another SBC application is if the placement in the manifold, the distance to the cam or the cam gear size itself was changed. I have never seen this, though I have seen issues with the precise alignment of the dist hole in some AM manifolds. As far as I know and I've been at this a while now, all the SBC distributors are dimensionally interchangeable. Melonizing is a soft powder coating over a hard steel gear. It allows the gear to be used with a roller cam that doesn't have an iron dist drive gear.
Pretty much any cam grind you want is available today with an iron gear. If you don't find your selected grind this way though a major brand company, contact your local cam grinder and they will grind it for you.
It's a simple matter of grinding the cam from a core that has had an iron tail section, which includes the gear and rear bearing journal, pressed on. It's really more a matter of the tail section being heated very hot and dropped onto the shaft, then cooled. I can't think of any reason why anyone would ever use a cam without the iron gear. I suppose if you're a serious racer and tear down a motor after every race day, then it doesn't matter as much. Otherwise, you're just creating more work for yourself by using the wrong cam core.
Seems like I have gotten things mixed up,.... sorry if that's true.
I have an 87 camaro with the dreaded lg4. Lookin to ditch the cc dist and carb, ive got another quadrajet to put on just need a distributor. apart from the electrical pigtails which is easily rectified, would pretty much any vac advance distributor for the 82-86 305/350 sbc work?, or is there something different about it? ie the gear on the bottom etc?
My first post was intended to point out that the distributor gear from the small cap (87) distributor will not fit on the shaft of a vac advanced distributor, because of the SHAFT SIZE. ( not the diameter of the gear. )
Originally Posted by naf
I just this weekend swapped a small cap dist gear onto a large cap HEI. Stock 'white box' large cap HEI and an MSD small cap that was in my '87.
I've got a couple stock style small cap and large cap dists in the garage. I may check their shaft diameters this weekend.
Might want to double check that gear; the fit of that MDS gear on a stock large cap distributor shaft might be a little "sloppy".
I think the stock GM HEI diz uses the .491 shaft. BUT... The external coil computer controlled HEI used the smaller .427 shaft. The .500 shaft is used by aftermarket MSD dizzys only,
I distinctly recall pulling the distributor gear from a STOCK 88 small cap and trying to fit it on a aftermarket vac advanced large cap distributor,...... and it did not fit. When I tried to find a replacement I learned that the roller cams used a hardened - or melodized - distributor gear. If you get a big cap distributor and plan to install a hardened gear - just make sure it's the right size. If you simply install the big cap distributor on a roller cam I'm sure the car will fire-up and you can driving it. Will the gear last last,... IDK because I have never just dropped a big cap distributor on a roller cam without swapping the gear. ( I've done this twice; the first time was described in an earlier post,... the second time was an 87 engine/cam and an aftermarket large cap vac advance distributor. )
I'm not alone thinking that the shaft size changed - am I ??
I'm sorry. I can't say that the dist shaft size didn't change, only that the outside diameter and fitment to the camshaft, overall fitment to the engine is the same throughout. You may be correct that the shaft size is different. I will measure the ones I have to see. I can compare a 67 breaker point to a large cap vac advance HEI of undetermined vintage.
Did the comparison. The shaft diameter is .490" on both the 67 points unit and the HEI. I don't have an EST V8 unit here to compare.
Ive ordered a big cap HEI. I was just wondering though, seeing as though this car had the small cap with no ground strap, do the big caps have a grounding strap/point or do people generally run one themselves?
The dist is grounded through the clamp. GM never installed a ground strap on any of their distributors because it isn't needed. Your small cap didn't have one either.
One last question regarding this - i havent had time to investigate, but from the old external coil i had 2 connectors with 2 wires in each, on the Passenger side i had the red 12v connector and a white wire that disappeared somewhere into the car, then the drivers side had a 2 wire connector joining to the ICM
would i be right in guessing that the white wire on the battery/Passenger side goes to the tach?
10-24-2016, 08:03 PM
) 
