RotaryResurrection

iTrader: (25)

Look man, I know you're a big proponent of turning down the cam. I've done HOURS of searching and reading on this forum during my teardown and rebuild attempt, and have read many posts of yours in which you recommend this.

However, it seems to me that the lack of uniformity is not with the cam, but with the bearings. As nearly as I can measure, the cam journals are PERFECT. Yet the cam bearings are the opposite of uniform. So why give attention to the cam, and not the bearings? Also, who is to say I won't want to change the cam one day, and have to have the new one machined to the same specs before I can use it?

It seems to me that turning cam journals would still leave you with an uneven bearing surface and you could still have wrong clearances...as the "high" spots on the bearing are now at the correct clearance, but the other areas of the bearing are now too loose and not even doing their job anymore because the cam journal is too small. Or, put another way, it seems like you're trying to get me to set my clearance to the high spots on the bearings. Well, what happens in 10k miles when those high spots are worn away? It seems like the clearance would be way too loose then.

Also, it seems like I don't have the greatest selection of machine shops around here. The guy I usually use to turn flywheels stated that he can't turn a crank or resize rods, he just usually polishes cranks and hones blocks. The shop I finally settled on who claimed to have "a little" LS machining experience is over an hour away and is not very good at communication.

I do not seem to be able to get the information I'm truly seeking here. Let me try a different approach.

I have read in some places that GM line hones the cam bearings after they are installed. Is that the "correct" procedure for building an LS motor?

Are there not enough professional/aftermarket LS engine builders here for us to truly know the best/most common way to do this?

KCS

iTrader: (20)

Who said a bearing should be uniform (ie concentric) all the way around?

RotaryResurrection

iTrader: (25)

I'm not really sure how to respond to that. It's my belief that the purpose of a bearing is such, yes. Why would it be anything other than perfectly round by design, except for mistakes or imperfection tolerances in manufacturing?

KCS

iTrader: (20)

Main and rod bearing ID's are eccentric by design. The race bearings are even more so. The purpose is to create a hydrodynamic wedge, which is what keeps the journal and bearing from coming into contact. The loose area acts as a reservoir so that as the journal turns, it picks up oil and squishes it into the tighter area, creating a high pressure "wedge". Have you ever wondered why you check bearing clearance at the 12 and 6 o'clock positions and not near the parting lines? That's where the tighter clearance is.

In the cam bearings, the loose areas will serve the same purpose. They'll hold a reservoir of oil to be picked up by the cam as it turns. You're main concern should be that you have enough clearance in the tight spots so as not to cause damage or excess friction.

If cam bearings were like main and rod bearings and were available in std, x, and .001" sizes, I would prefer that instead, but we don't have that option. Instead, I prefer to turn the cam down, which usually only .001" or so is required. I'm lucky in that I'm local to the same grinder that LME and HKE uses, but any grinding shop should be able to grind a camshaft.

Like I said, I've seen both ways work, but that's my preference. When I had .0005" clearance on my cam, I didn't waste days swapping out bearings or scratching them up to open the ID up. I wrote down my measurements, dropped off my cam, and one day and $30 later I picked up my cam and continued with my build.

machinistone

The boring of the cam tunnel happens in two steps, from the back and the front, so they're not always in perfect alignment when you install aftermarket bearings. I would say that 1/5 of these motors has misalignment issues where the bearing needs to be scrapped on one side in order to correct a binding issue. This scrapping is done with a bladed tool, not scotch-brite, and it's how all bearings were hand fit before modern methods of manufacturing made them mostly acceptable for use out of the box. Carefully scrapping a bearing in the right place to gain clearance will as a fact result in less oil loss through that bearing, and a more uniform result than simply polishing or grinding down that bearing journal on the camshaft.

I much prefer the one-piece Durabond bearings, specifically the hard teflon coated performance series CHP-23T, or at minimum CHP-23 - these motors can be hard on the narrow bearings and you need a material with good load handling ability. If you have a Durabond book, getting the right bearing set is as easy as measuring the hole on the front and back, obviously calling a parts house and expecting them to send you the right set is a crap shoot, it's not something as simple as an alternator and even that they'll screw up with regularity.

RotaryResurrection

iTrader: (25)

UPDATE:

I think I have resolved the cluster to my satisfaction, finally.

As of my last post I had installed the clevite bearings, all of which were tight and irregular, and hand clearanced them so that the cam slid in and spun relatively freely, but the clearance was still on the tight side. I was not really happy with it, especially after reading the comments in this thread.

So I bought a set of durabond CHP-23T bearings. I pressed out all the clevites and wiped the bores clean again with brake cleaner. I chamfered both inside edges and oil holes of each durabond bearing with a razor knife to remove any irregularities. I pressed them in using my modified press tool (big thanks to ckpitt55 for the help on that).

Slid the cam in like butter and clearances are perfect. Slid it out and there's not a single high spot/rub mark on any of the cam bearings. I'm very happy with it at this point and I can finally build the damn thing and get the car running again.

Thanks to everyone who posted helpful information.

Brian's Auto

the mains need to be installed and torqued before the cam bearings are installed

G Atsma

You are responding to a 7-year old post. I have a feeling they solved the issue by now.