ckpitt55

iTrader: (4)

I posted this in my build thread but figured it might get lost in the shuffle there.

I'm assembling a freshly machined shortblock with new cam bearings (stock size). The journals on my cam all mic'd fine, but my clearances were all on the small side.

The vertical clearance measurements (measuring from 12 to 6 in the bore) were all tighter than the horizontal measurements (measuring from 3 to 9). Bearings 1-4 were between 0.0021-0.0023" in the vertical direction and 0.0023-0.0025" in the horizontal direction. Bearing 5 was tighter however - 0.0016" vertical and 0.0019" horizontal.

From what I've read these all seem to be on the tight side - seems like most guys like to run ~0.003". I can get my cam in the block, but it does not spin without assistance from a wrench. The turning effort is consistent though, doesn't bind in any spots. Should I be able to spin the cam freely by hand or is some resistance with fresh bearings and and a new cam to be expected? Is there anything I can do to open them up a bit, maybe use a fine-grit ball hone?

Thanks for any input.

gMAG

iTrader: (1)

I don't know what my cam bearing clearances are, to compare.
Mine moves, as long as it's being turned...and maybe 1/3 turn more. It won't spin, though. No binding, with a smooth turn, bearings have some minor wear....with 35k miles.
Does it take a wrench to turn it? Can you turn it by hand?

KCS

iTrader: (20)

My clearances were tight, so I had the cam journals ground. Turned over by hand after that.

huggerorange69

iTrader: (7)

I put new durabond cam bearings in my motor and they were the same way, you couldnt turn it by hand but very little effort it would turn easy with a wrench. I went ahead and put mine together.

ckpitt55

iTrader: (4)

Takes a wrench to turn it. once you break the static friction though it doesn't require all that much effort to turn, and it is smooth.

I'd rather massage a $40 set of bearings than permanently modify a $400 cam, but that's just me.

did you measure your clearances? if so what were they? I'm using clevite bearings if that makes a difference.

Am in the ballpark for clearance spec? Is 0.003" a good number to shoot for, and should you ideally be able to spin this by hand? I realize this may be a "feel" thing, I just don't want to have oil pressure problems and/or run the risk of spinning a cam bearing, though I did install them with some loctite sleeve retaining compound to help prevent that.

Another thought - would installing and torquing the main caps have any effect on cam journal alignment? If the block was originally machined with the main journals installed it would make sense if they did (in a similar way to torquing the heads affecting the cylinder bore shape).

Guess I'll try that out to see. If that doesn't improve it I'm going to try taking a fine grit hone to the bearings, finishing with scotchbrite/steel wool and then cleaning thoroughly with ATF to remove any abrasives. If I mess them up, who cares, it's $40 for a new set.

huggerorange69

iTrader: (7)

Ive put together tons of sbc gen 1 motors and you could always turn the cam with your thumb on the cam dowl. This is my first ls build. Mine did the same thing with the mains torqed down. After i put the crank in and put the timing chain and oil pump on it feels like any other engine ive put together. I took some steel wool and mineral spirits to the bearings and that seemed to help just run it around them a couple times. I washed out the block really good after that and it seemed to help.

KCS

iTrader: (20)

I'd rather grind the cam .001" rather than take a ball hone or sandpaper to the bearings. Its a lot easier, a lot quicker, and won't hurt the cam at all. It's not like you're going to ruin the cam.

ckpitt55

iTrader: (4)

It'd be a different story if all my clearances were uniform. I'd be inclined to grind the cam as you suggested if they were, but in my case since #5 is the only anomaly, I'd end up with one journal that was a different size than the rest to gain the necessary clearances. That doesn't make sense to me, especially when the journals are cherry as is and the bearings are going to wear to fit the cam journals anyway. Bearing scraping / honing is not a new thing. I'm gonna give that a shot first, if it's not effective then I'll look at other methods.

ckpitt55

iTrader: (4)

Did a little bit of messing around last night, re-did my measurements as a sanity check and got the same results within a few tenths. Seem to be ok bearings 1-4, tight on 5. I installed the cam one lobe at a time, checking for resistance and it can be spun by hand when installed up to the 4th journal. It gets tight as soon as you try to move into #5. Looking for high spots, it seems like the interior edge of #5 is having contact. Before I remove any material I think I'm going to hammer it out and try reinstalling it, seems as though it might have gotten cockeyed despite my efforts to keep it true. There also seems to be some high spots near the oiling holes on some of the other bearings, so those may need some touching up as well. The tools should be coming today, I hope to make some progress on this here in short order.

Grimes

iTrader: (3)

nice. props to you for actually checking. most people would just slap a new cam in and go...."It'll clearance itself on the startup!"

3rdCoastPowerSports

iTrader: (5)

We went through a few box's of Durabond cam bearing just the other day. it took three boxes to find a #3 that would fit without binding. From what it seems lately there might be some bad (manufacture defect) cam bearing out from before mention manufacture.

ckpitt55

iTrader: (4)

no kidding? that's interesting. were there any burrs or anything you could see? I took a bearing scraper and some scotch brite to the leading edge chamfer and over top of the oiling holes and the action seemed to improve greatly. Seems like they must drill the holes after lamination of the bearing is complete, and the drill bit mushrooms the material surrounding the hole leading to a high spot. The nature of installing these things is hard on the bearings too, pretty easy to crush the hell out of em if everything isn't lined up perfectly. 1-4 in my block feel great, 5 is still binding up. I'm going to pound it out tomorrow and try reinstalling it to see if that helps things at all.

3rdCoastPowerSports

iTrader: (5)

I always hit them lightly with a bearing scrapped. The bearings themselves looked normal, block looked good (not perfect but nothing that would cause any issues). I wasn't doing anything different installing these than I do on any others. They just weren't fitting properly. Now that i think more about it #5 gave us a hard time as well. Lined it up and put it in perfectly strait. No burs or ridges on either the bearing or in the block. Like i said, went through 3 boxes before finding all that fit properly. The only thing i could think of was manufacture defect. Sent the non mangled ones back to Durabond but haven't heard anything since. USA sure doesn't mean USA anymore that's for sure.

ckpitt55

iTrader: (4)

sad but true