I need a little info and help. I have a small block 400 that has bad lifter bores. The cam eats up in it, the bigger the cam and the heavier the springs the faster it eats up. In looking over the cams that have been in it I see where the passenger bank is only wearing on the back 1/4th or so of the came lobe. The other side is wearing on the forward half of the lobe. This seems to be the problem, everything else in the valve train looks good. To find a new 400 block ain't easy these days. To fix the lifter bores costs $$$ since its a special race machine job, plus the machine shop told me a minimum wait of a month. I was looking in to getting a roller cam. It would seem to be a work-around for the problem since it doesn't depend on the lifters to spin right and contact the cam exactly right. What do you guys think?

I was looking at the XR282HR grind from Comp Cams. I was curious if anyone knows if this cam requires a special cam gear or if it can work with the regular old Chevy iron gear. I know a cam button is needed and special push rods. Other than that are any other special parts required for the change?

Almost forgot. Does anyone know if this cam already comes in a reduced base circle, or at least if its available that way without paying a ton extra?

Thanks in advance.
Grand Prix

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

 

You can use a standard double roller chain and gear set. I would also use a thrust bearing and cam button. Make sure you check endplay of the cam.

All comp hydrollers are standard base circle. They just told me last week that there is no extra charge for a reduced BC hydroller. They quoted me 258, for a custom grind. But, the reduced bc size is only .050 smaller than standard bc. That does not get me the clearance I need with the SCAT I beam rods. I need close to .100 additional clearance.

 

Thanx.

I am a little confused about the "wear plate" I saw in a catalog. I am not sure if you have to machine the block for it or not. In the past someone told me that timing chains with thrust washers need the block machined to make room for the washer. Could I use either a wear plate or a thrust washer timing chain without block work?

It sounds like Comp Cams sells directly to people, is this true? Do you know the part number for the XR282HR in a reduced base?

Did you have an opinion on this solving my problem?

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

 

the block really does not need modifying. But the top gear does. Once you talk getting the top gear machined (about 25 bucks) and then the thrust washer from summit (about 12 bucks) you could almost get an gear/chain set already cut with the bearing/washer. Summit also sells a whole gear/chain set with washer and top gear machined. About 65 bucks (I just got one).

The code comp gave me was
12-000-8-1.050 bc (the 12 means it is a retro-fit hydroller). You then tell them what lobe grinds you want on Intake and Exhaust and what lsa. Yes, they can do it from the 800 number.

I really don't understand the problem to well. If you lifter bores are not straight and true, I don't know if the roller will fix it. You might run into problems putting the lifters in the bores since they are attached to each other. In many cases, there is not a lot of room for error on rollers, if the roller moves very far off it's intended path, it will strike another lobe (very bad deal). I think that's the main reason for the thrust control.

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

 

Lifter bores that don't point at the cam are a common occurence in 70s blocks. It's nearly as common as the ones where the starter bolt holes are drilled wrong.

I can't see where a roller setup would survive for very long with the lifters at odd angles, any more than a flat tappet system would. The roller will only run on its very edge, and at the very edge of the lobe; the concentration of all the force like that is beyond the design of the parts.

I have that cam, in a std base circle, in my 400. It runs pretty good. You use a regular timing set (true roller, of course, but regular other than that) and a cam button. The push rods aren't "special" either, they are merely shorter than what you would use in a flat-tappet setup because the lifters are taller. Comp makes push rods in .050" steps over a wide range all around the lengths you'd need. IIRC the ones in my motor ended up being 7.550", but my memory could easily be off. 7.800" more or less is the length for stock ones.

Why are you concerned about the base circle?

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"So many Mustangs, so little time..."
ICON Motorsports

 

OK. Looks like a new timing chain would be a good idea. The block's problem is that the passenger bores were drilled all at once, and drilled too far towards the back of the block. I can (and would) measure the spacing for each pair to see if its pretty close to right. I don't think they are horribly off or else I would already have the cam smacking the lifters. I guess some more measurements are in order. Thanks for all the info.

 

Well that is a little more hopeful of a situation. A possible approach might be to make some shims that you can use between the cam gear and the end of the cam, to space the cam rearwards slightly. I wouldn't get too carried away with that though because you'll get to a point where the dist gear won't line up right any more.

Unfortunately the only way I know of to make sure that everuthing fits, is to buy the parts and install them and see where they end up.

As far as the oil hole problem with the smaller circle cam, you could have the lifter bores grooved. And, to get a really small cam, you should be able to get them to grind it on a billet core rather than cast. AFAIK there's no reason that wouldn't work; they just use the cheaper cores for the hydro rollers to hold down the cost.

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"So many Mustangs, so little time..."
ICON Motorsports

 

unfortunately rb i have recently talked to comp about reduced bc for hydrollers. They say they can't go smaller than 1.050 (about .050 smaller than normal) because of cam breakage. The hydroller cores are made of a different material than solid. They might be able to grind a hyd-roller lobe pattern on a billet core, but you would still need a bronze distributor gear.

 

Glad to find a few people with a little experience in these cams. I was thinking about moving the cam in the block to split the error between the banks. Your idea sounds good, or I might be able to mess with the shims/gear/thrust a little. I think as long as make sure everything I put in is flat & doesn't move it more than 0.010"-0.020" I should be fine. If I need more than that to split the error then I will probably have problems with the rockers anyways.

I know this is a little odd and its hard to be confident it will turn out ok. I just wanted some input to see if I am completely crazy or if this can actually work. I need to pull the whole engine and waste a bottle of machinests blue to make sure all the rollers are running flat and hitting the cam right.


The reason for the reduced base circle is clearance. I think I will be ok. But if the same price buys a reduced base from the get go then chances are better I won't hear that horrible thunk when I turn the engine over. Then even if I do it means less grinding to get my 0.050" clearance. Tell me, what have you been doing for rods to clear the standard version?

 

My rods are stock... no grinding whatsoever. I do have the ARP bolts with their shoulders chamfered off though.

You're right jcb, if you used a billet cam, you'd need to change the dist gear; I think that would be a small added expense / difficulty if the billet cam would clear up the issue though. I think you should at least research that route.

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"So many Mustangs, so little time..."
ICON Motorsports

 

it looks like the billet hydroller is my only option. The folks at cammotion don't think I need it but they don't realize how hard that thing hit when i was turning it over. It needs a LOT to make it clear.