jcb999

I just thought a reduced BC cam would fix my problem. It seems that hyd-rollers can't be reduced to the same diameter as a solid roller. Most reduced bc cams are .9" (comps) and .96 (crane). Standard BC is 1.1. Comps hyd-roller reduced bc is 1.050. (that only gets me 50 thousands. Cam motions is 1.040. I did some more checking on the scat cap screw I beam rods I got and in some areas, they are as much as .120 thicker than the X rod (it had the bolt heads ground down) used in the previous shortblock.

So, I am going to need to take off .050+ (some of the scats are thicker in that area than others) even after getting the reduced BC cam. Or find a way to get them to grind it on a .9" bc.

Folks, don't do what I do. This is not the good way to go about it.

Vader

JCB,

A few more options are Iskendarian, Crower, Lunati, and probably some others I'm not aware of. Comp has the ability to grind an 0.875" base circle, and possibly less on a custom order.

You could also shop for different rods. There are several brands that offer high clearance designs for stroker applications - Crower Sportsman, Manley Racemaster both advertise clearance up to 3-7/8" strokes with a stock cam.

Just how close are you?

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Later,
Vader
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"Let the bodies hit the floor!"
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89gta383

iTrader: (5)

Why don't you just run a solid roller then?

jcb999

Unfortunately, I sorta of backed into using the 4340 scats. I really don't like h beams bc of the weight and I was under the impression that these I beams did not have too much clearance issues.

When i turned it over with the existing hydroller it hit real solid. And I really don't think much material can be removed from this bolt boss.
http://www.scatcrankshafts.com/4340Ibeamrods.jpeg (never did hear back from scat).

it's looking like solid roller is the only option. I did have all the valvetrain setup for hyd-roller already (including an afr hydra rev). I really did not need the rpm a solid roller could provide. I really don't need to rev it past 6200.
I am going to call some folks again monday and see what the deal is with smaller bcs.



[This message has been edited by jcb999 (edited June 17, 2001).]

Vader

Have you called the Comp help line and checked the possibilities? (1-800-999-0853)

------------------
Later,
Vader
------------------
"Let the bodies hit the floor!"
Adobe Acrobat Reader

jcb999

Yea, I had talked to comp last week. They said 1.050 was their rbc size. I am not sure if it is the only size.

I am afraid that one of the issues with going smaller is the oil holes for the hyd-lifter. I bet they don't line up after anything more than about .2 smaller (maybe less)

I think the material they make hyd-rollers out of is differnt than solid. Knowing my luck they can't get a core smaller than about 1.04

[This message has been edited by jcb999 (edited June 17, 2001).]

jcb999

comp says they were breaking cams when they used went any smaller than about 1.050. The material is more brittle I guess than the billet steel used in solid rollers. Cam motion said that might be able to go down to 1 inch. I am waiting to hear back from them.

jcb999

Cam motion said they could grind it on a billet core. I think it would be as small as .96. So that would work. I would just have to use bronze distributor gear. Which is a much better option than a solid roller as far as I am concerned.

But, actually they thought I really did not need it. I am going to call back tuesday, and talk to the expert (who was welding at the time). I am afraid they don't know how much material I would have to remove to make it work with their base circle of 1.040. I don't even know for sure but its enough to make the threads on the bolt boss area visible from the outside I think.


[This message has been edited by jcb999 (edited June 18, 2001).]

jcb999

i just called scat. they said oh all you have to do is cut the bolt boss at a 45 degree angle. They dont say how far but.. then they said that the bolt would have to be shorted also. WTF? I don't think that would work too well. They supposly have a place in houston that modifies them the way he explained. I might get a look at a set from the place in houston hopefully.

I mean I don't have a problem with a reduced bc cam, but I really don't want to go to the trouble of a rbc cam and still have to modify the rods.

Grand Prix

Have you talked to Crane recently? I noticed in looking around myself that some of their hyd. roller cams come standard in a 0.9" base circle. Maybe this will work out for you, maybe it was just a misprint. But I think its worth looking in to.

jcb999

Yeaha.. i think I am fixed up. Cam motion has a .925 inch core that will work. They said i don't even have to use a bronze gear. That is .175 smaller than the factory size. That should make it fit no problem...



The only problem I might have is with the AFR hydra rev. I don't think the spring tension will be right with .175 less preload. I might have to get bigger springs or a thicker plate that goes under the head.
AFR does not make bigger springs. It looks like I need a thicker plate for under the head.. I just have to find some aluminum stock now.

After all the other BS I have been through, I think I can pull this off.

I could not find any reference to reduced bc on cranes web site. The only reference I have seen for crane is on solid rollers.

I see them now http://www.cranecams.com/master/apps/chevy18.htm

But that only seems to be on two of them. I don't know what the BC is on their others.

[This message has been edited by jcb999 (edited June 20, 2001).]

Craig Moates

I'm trying to put together a 383 right now with 5.7" Scat 4340 I-Beam rods. The cam I have is a Cam Motion with a 1.08" BC. The rods get into the cam tunnel about 0.15" when I look down there with no cam in.

So what should a person do? On one hand, find a cam that will clear the rods. On the other, take a little meat off the rods. Problem for the latter is I already balanced everything! Also don't know about strength for taking a 0.2" corner off the boss. To clear for sure without taking off meat, I'm guessing I'll need a base circle of around 0.8" for a 0.55" lift (1.5) cam.

Anyhow, if I knock the same amount off each rod boss, can I get away without rebalancing? What about strength? I'm kinda worried here, this is slowing things down a bit. Advice is welcomed!

-Craig

Grand Prix

Wish I had a good answer for you, but I'll add some commentary and maybe you can decide where you want to go from here. The amount of metal you are taking off of the rods should not throw the engine out of balance badly. Yes it will affect balance, but a street engine doesn't need dead on balance anyways. If you are careful and take the same amount of metal off each rod you won't require balancing. All that will really be off is the crankshaft counter weight. The engine will not be as well balanced as it was before. As a 383 the rods should have been clearanced as soon as you got them. The rod strength should not be an issue, for aftermarket rods in a non critical area like that it should not matter.

I don't know how much cam motion charges for a special 0.925" base circle cam but it may be expensive. The only other offer I can make is the crane 119651 is a 0.860" base circle cam. It is one of the cams I was talking about before and is a fairly large cam for a street 383. This much base circle reduction is going to mean different length pushrods and the cam has a possibilty for twisting and breaking. I think myself the choice would go this way. If its a street engine, grind the rods. If its a race engine, get the larger crane cam with the reduced base circle and grind as little as possible afterwards. It is your choice, so do what you feel the best about.

jcb999

Just been there. Got a .9 inch reduce bc from cammotion on thursday. It clears my scat rods fine with .050 clearance. I had called several machine shops in houston. (sounds like your close to them). One said they will modify the rods (they knew which ones it was and how much needed to be removed) for about 40 bucks. One place said rebalancing was needed, another place said it was not because the weight is so close to the crank centerline (i think if you take weight off of all of the rods, rebalancing is not needed, just equlize the weight).

I think one place was houston engine and balancing and the other was sun engines. Sun was the one that did not think rebalance was required and they said they build a lot of 383s with those rods. They also said someone could do it by themselves. But considering the way the rod bolt goes into the threads, I would much prefer have it done on a bridgeport mill all at once.

What i did not like was how the threads for the rod bolt went all the way to the end of the rod. If you cut much more an about .1 inch, of that, the bolt will also be getting cut.

My .9 cammotion was 50 bucks more than a standard BC. Since most hydrollers don't have anywhere near the spring pressure that solids do, cam breakage should really not be an issue.

Try to find one with the bc ground on an even tenth (or .050) of an inch. Most pushrods come in .050" increments. Otherwise, you will have to have a set made.

PS. my cam-mot has a cast iron distributor gear. So a bronze gear is not required. Most of them are being made like that now.

Good luck friend. I feel your pain.



[This message has been edited by jcb999 (edited July 02, 2001).]

Craig Moates

What's the grind number of your Cam Motion unit? They're right here in town (Baton Rouge), so I could pester them in that respect. Thanks for the advice!

After some inspection, it turns out that the solid lifter (non-roller) cam I was thinking of using (1.05 BC) is pretty wiped, like 1/8" off the lobes. No go! I think I'm going to go hydraulic roller retrofit now. Seems there is a lot more flexibility in custom grinds for the roller cams. opefuly (and your testimony indicates it) I can get away without grinding the rods at all, I've got a race balance on the assembly right now (+/- 0.5gm dynamic), and it would be good to keep that A-OK.

Were there any special considerations with respect to the angles for clearance, or did the BC alone take care of things?

Thanks again...

jcb999

you got e-mail..

So far, it looks like the reduced bc will do it. I need to check a couple of more rods to be sure. I think some scat rods are slightly thicker in this area than others. I plan on using the thiner ones in the cyls 1,2, 5 and 6.