gojoe

A little background, I bought a HT383 from GM Performance in 2002. Motor ran for about a year then spun a bearing. Took motor to local shop. While I was at it ordered bigger cam and machined Vortech heads for the bigger lift, Also wanted all forged parts to go with the forged crank. The shop offered to let me put it together at there location with there oversite so I could learn how to do it myself.

To the point, when assembling the engine the new rods where hitting the cam lobes, pulled apart and took some material off of the rods on one side. Put it back together and used a small mirror to eyeball the clearence between the rods and cam. To say the least I'm concerned that if the timing chain stretches or I spin another rod bearing that I'll have a pile of junk. The motor runs good right now and has already made it longer than the first time.

Is this something ppl do all the time or should I pull apart and put a different set of rods in while I still can. The clearence apears to be at most 1/16". This is a one piece rms roller cam moter. I'd like to keep it awhile.

Sonix

iTrader: (1)

Usually 1/16" is the bare minimum that people recommend as that clearance.

It's ultimately your call now, only you saw how much clearance there was, and only you can decide if it's worth it to change that now Are you using a camshaft on a small base circle? That's the easy way to get more clearance there.

sofakingdom

iTrader: (1)

Right; .050" - .060", slightly smaller than 1/16", are the usually quoted #s.

People often use a regular plastic tie-wrap as a go/no-go gauge.

Yes it it risky, no matter what. If something breaks, the cam gets totalled.

Since a "bigger" cam is actually physically SMALLER (the tip of the lobes is pretty much always as big as it can be and still be able to slide through the bearings to install it, they make a cam "bigger" by making the "heel" of the lobe SMALLER) it should be a better fit than a "smaller" cam.

I didn't know Vortech had started making heads; I thought they only made centrifugal superchargers? What are their heads like? What kind of flow #s do they have? What intake runner sizes and chamber sizes and stuff like that?

gojoe

How much more clearance will the small base circle cam give me? Is there other parts that I'd need to change for the small cam ( pushrods, etc.)?

Thanks for your time and info.

sofakingdom

iTrader: (1)

A typical small base circle cam is on a .900" BC instead of 1.000"; so it's .100" smaller. You gain half that clearance, or .050". Typically you need push rods that are longer by that amount, than an otherwise identical cam and valve train setup with std base circle. Sometimes also you need lifters with their oil feed groove up higher on the body, so that as the lifter descends that extra .050" into the block, it still preserves the oil passage.



Like these.... (std on right, "special" for sm BC on left)

But not often. I'm guessing, from the type questions you're asking, you're nowhere near this point yet.

gojoe

The Vortech heads I mentioned are the ones from Gm Performance Parts, they came with the HT383 crate motor. I'm sure you have heard of them. I might be spelling Vortech wrong. If you have not heard of them let me know and I will look up the flow #s. They have a 170cc intake track, so they are a bit small for the 383. But they can be had for $500 brand new. They still provide 416 rwtq on the chassis dyno, only 368 rwhp. The cam is a extreme energy with around .520" on the intake at .050".

Sonix

iTrader: (1)

Which do you think is easier sofa, small base circle, and pushrods, or grinding rods (and perhaps balance issues?).

Yea, it's Vortec. Vortech is a company who makes superchargers. That "H" is a big deal.

gojoe

not at .050"

gojoe

Thats another concern I had about the grinding we had done on the rods, The grinding was done after everything was balanced. They told me that it would not hurt the engine. I cant tell with the engine running but it might not be detechable by the seat of my pants.

gojoe

Sounds like I'm lucky the thing runs, because I had other problems also. Like Roller rockers hitting retainers and breaking the cheap screw in rockerstuds. Thats an awful sound to here from a rebuilt engine, pushrod hitting the valve cover, sounds like catastrophic failure. Ended up putting ARP screwin studs and grinding the rocker for clearence. Also the oil pickup feel off once. Thats a pain to fix in the car. Think I'll pull it out while it still runs and do everything right.

sofakingdom

iTrader: (1)

Oh, THOSE.... right, I think I may have heard them mentioned before maybe once; if it's the same ones then they're Vortec (GM tradename for "intake ports are in a different place") as opposed to Vortech (the blower mfr). 2 very different trademarks with very different meanings, and not to be confused.

I will not grind on rods except as an ABSOLUTE LAST RESORT. Possibly compromising their structural integrity is something I don't take lightly. Before or after balancing. But most certainly not after balancing. Because once that is done, they need balancing again. Kind of economically inefficient.

I'll grind the block and fill it, and run a sm BC cam, in order to avoid touching the rods.

Small BC cams are fine, for most applications. By your specs what you have is just a hyd roller anyway, the XR282HR specifically; a fairly mild cam, and being a hyd roller, should have no more than 350 lbs or so of spring pressure over the nose. In fact, compared to an off-the-shelf XR282HR, a sm BC one will be ground on a billet core, instead of the cast core; so it would actually be a better cam all the way around. With a solid roller, and 600 lbs or more of pressure, there might be some cause for concern; but not in your case. It would be perfectly fine. I don't have any problem with the slightly longer push rods also.

With a little street cam like that, no need to worry about the oil groove thing. Those lifters in the pic are solid rollers, for cams with .650" -.700" kind of lift, WITH the sm BC. A whole different league, let alone ballpark, from what you're working with. I don't think you can even get them made that way for hyd rollers but I could be wrong.

gojoe

Thanks for taking the time to help me out.