Hi,

I have a 88 Firebird with an LB9 roller cam engine and it has been fitted with a HEI dizzy - I have searched the part number (1112977) and it looks like the HEI was used in the 76 Camaro.

Thing is, I have read a lot of conflicting opinions as to whether or not the drivegear on these older HEI units is o.k for use with the factory roller cam.

As far as I can gather from what I have read, the FACTORY roller cam is cast iron, as would be the '76 cam - so will the dizzy be o.k for use with my engine?

I have also read that AFTERMARKET roller cams are usually made of billet steel and these need a soft bronze drivegear on the dizzy.

I don't think the car has done many miles with this combination, but so-far there doesn't seem to have been any wear - the timing seems steady when veiwed with a strobe light.

Am I on the right track here - any advice/ suggestions would be much appreciated.

Thanks.

 

From what i understand, the roller motors camshaft tends to "walk" and the brass gear is more forgiving with the gear mesh than the steel. hope this helps

 

It has to do with the relative hardness of the two gear materials.

Before the factory started using roller lifters, aftermarket roller lifter cams were made from billet material, which was very hard (to withstand the line contact the lifter made with the lobe). The hard material extended to the distributor drive, which would wear out normal distributor gears. So, brass was used, and since these were typically off-road engines, regular rebuilding included distributor gear replacement.

When the factory started going hydraulic roller lifters, the lift wasn't as high as the typical aftermarket race cam, so the valve spring force didn't need to be as high. Therefore, the contact line force is lower and the camshafts didn't need to be as hard. They also made the distributor drive softer, so all that was needed for the distributor gear was a surface treated part. The factory calls this a "melonized" gear, so putting one on an older factory HEI is probably a good idea when using an old distributor on a factory roller cam. In fact, they stopped making anything but this surface treated gears, so if you get a replacement gear from the dealer, it will be compatible with your factory roller cam.

 

Thanks for the quick reply five7kid, I am looking at a replacement distributor on e-bay - made by Wysco, with a '4340 Chromoly Steel bottom Gear, for use with cast and Steel Billet Cams'

What do you think - ebay item no is 260124601248

Thanks,

Mark.

 

Any ideas anybody?

I am looking at a replacement distributor on ebay - made by Wysco, with a '4340 Chromoly Steel bottom Gear, for use with cast and Steel Billet Cams'

ebay item no is 260124601248

I have a 88 Firebird with an LB9 roller cam engine and I would like to know if this distributor would be suitable.

As far as I can gather from what I have read, the FACTORY roller cam is cast iron, so will the dizzy be o.k for use with my engine?

Thanks.