Generation IV Internal Engine - Cam bearings .002" smaller ID




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Ls2 cruiser
07-21-2012, 09:38 AM
As the title says, I am looking for cam bearings that are .002" smaller internal diameter. The clearances I have at the moment are 1 and 5 are .0055" and .0045" and 2,4 and 3 are .003" which is ideal. Either that or another way to bring the clearances back to ideal. I cant find any bearing manufacturer that makes .002" oversize bearings as they do with early chev, ford engines etc.. The engine is a Ly6 which has the same cam bearings as a ls2. Any help would be great.


dickieirish
07-22-2012, 12:52 AM
:bomb:

Ls2 cruiser
07-22-2012, 08:33 AM
Can the stock cam bearings be moly coated to build them up .002" smaller in internal diameter to make the clearance smaller?


stevieturbo
07-22-2012, 05:44 PM
Factory specs do allow up to 5 thou I think.

As for measuring etc. Having had cam bearings move and lose all oil pressure...this is a major annoyance of mine !

First time I dont know why it happened, second time was my own doing DIY fitting new bearings ( and some old because cam wouldnt fit in after my installation attempt lol )

But even with brand new bearings, installed properly my clearances were all over the place. From just under 2 thou to about 5 thou. 1+5 were loosest, 2+4 were tightest.
The camshaft would go in and turn...but not as loosely as I'd have liked. Actual bore in the block, all sizes measured bang on spec. Due to different size holes it was impossible to measure alignment though of the holes.
But they seemed in alignment ok when the bearings were installed.

BUT, what did happen, and I was surprised. When I torqued up the main caps, the camshaft suddenly turned as you'd like it to. Very easily by hand. I never did remeasure the hole size though, to see if somehow tolerances had opened up on 2+4
So unless you are measuring with the mains torqued up, I do believe the measurements wont be valid

Given past issue with the bearings moving, I also drilled/grub screwed them into place. No way were they going to move again, and so far they havent

Out of paranoia I also fitted a Melling high volume pump, even though it isnt needed. I now have around 35-40psi at idle with around 70-80psi at high rpm.
Probably too high, but it'll be fine. I'm on 10/60 at the minute but will probably thin it down next change.

Ls2 cruiser
07-22-2012, 06:31 PM
Stevie, thanks for your info there. How do you pin them in more detail if possible.

stevieturbo
07-22-2012, 06:48 PM
I was advised against loctite by almost everyone I asked so didnt bother with it.

The middle 3 bearings are easy to pin. I just marked up the valley for the centre of the bearing, drilled a small 4mm hole down through the valley and bearing.
Then tapped this out to M5, but only just until it was poking into the bearing. I wanted the allen key grub screw to screw into the hole and bearing, but be a tight fit into the bearing. I then loctited these in place when I was happy they were far enough into the bearing, but also safe enough they could never hit the camshaft.

Positions 1+5 are slightly more awkward as there is no easy way to drill and tap.

I used one of these Desoutter 90deg drill's

http://www.aetools.co.uk/product-air-drills-angle-drill-collets-boelube-accessories-desoutter-compact-90-head-316-capacity-038-hp-1428-thd-129.php

This combined with a cut down drill bit allowed me to drill through the bearing and into the block.
I then cut down the taps, welded a hex nut onto the short tap so I could use a spanner to turn it and tap a hole through the bearing and into the block.
Again, depth was trial and error and I got M5 grub screws and screwed them into the hole so it was just below the surface of the bearing, again deep enough to be safe from the camshaft, but also to ensure the bearing can never move. Cant remember if I loctited those ones or not, but they are tightened into a blind hole and bottomed out.
Just make sure where you drill is a solid part of the block.
Depth of the holes would only be about 13mm or so anyway I think.

When speaking to people before hand, they did recommend grub screws that had a point, or small tip on them to secure the bearings. I couldn't find any so just used normal stainless ones I bought off egay.
I bought various lengths as wasnt sure what I needed. The middle 3 can be any length really as there is loads of space in the valley if they are too long.

stevieturbo
07-22-2012, 06:59 PM
Should also add. From memory, on mine sitting as a bare block with nothing bolted on at room temperature over the winter, so talking 40-50degF my clearances were

1 = 0.005"
2 = 0.002"
3,4,5 all around 0.003-0.004"

Positions 1+2 were most notable because of that huge difference. The cam was much tighter than I liked at this.
However, when the bearings were first installed, the temperature was warmer, maybe 60degF and it was looser although no idea on clearances as it wasnt measured then
The cam was easyish to turn, but still not great.

It was only when the mains were torqued up it turned very freely with no effort at all as a camshaft should do. Who knows what them happens when the heads are torqued up, I never did try.

Ls2 cruiser
07-22-2012, 09:26 PM
Thanks very much Stevie, a great explanation. I will ask my machinist but it might be too hard for him. lol

stevieturbo
07-23-2012, 03:35 AM
In short, if you're measuring without the mains and heads torqued up, you're probably wasting your time as measurements won't be valid as I discovered.

Ls2 cruiser
07-23-2012, 03:41 AM
Stevie, is your block alloy?

stevieturbo
07-23-2012, 03:42 AM
Yes, ls2

Quick Carl
07-23-2012, 05:28 AM
The Clevite SH 2125 are a little thicker (.001") and may help on 1 & 5. The 1 & 5 are slightly larger than spec from the factory (usually 2.348, compared to factory spec of 2.345- 2.347) on every block I've seen.
Generally we just pin cam bearings on extreme road race engines that will be running very hot for a long time.

Ls2 cruiser
07-23-2012, 05:41 AM
Yes, I have noticed when my ls2 alloy block was on a stand, you can crack off the main studs and the crank wont spin. You tension the mains back up and the crank will spin freely again. My Ly6 block does not do that. They are bloody heavy though. i can understand what you are saying about the cam because the block is bending or distorting on the engine stand without the mains done up. Try a support under the end of the block next time. What you are saying is that when it comes to actually fitting the cam to see if it turns freely, you need the mains tensioned. From memory, my cam turned ok in the ls2 as I fitted the cam first before the crank. Probably different clearances and I normally prop the block at the front when it is on the stand. So there is no way to reduce cam clearances apart from maybe having a custom cam made up with bigger journals on 1 and 5.

Ls2 cruiser
07-23-2012, 05:51 AM
Thanks Carl, that is the sort of info I am after. Just to make sure I understand what you are saying. The OD of the clevite bearing is on the large size. This would mean it has more interference on the block and therefore has less tendency to spin or walk out of its hole in the block. Will it reduce clearances between the bearing and cam journal by .001" though?

Quick Carl
07-23-2012, 05:59 AM
Thanks Carl, that is the sort of info I am after. Just to make sure I understand what you are saying. The OD of the clevite bearing is on the large size. This would mean it has more interference on the block and therefore has less tendency to spin or walk out of its hole in the block. Will it reduce clearances between the bearing and cam journal by .001" though?

Yes, they tend to be .0005" thicker and .001" diameter smaller as they are set-up for a larger OD, but the same I.D.

Ls2 cruiser
07-23-2012, 06:03 AM
Thank you Carl, you are a life saver. I will order some.

J-Rod
07-23-2012, 09:17 AM
Oil clearances will typically be in the 0.002 - 0.004 although some aftermarket bearings will be as loose as 0.006 and not casue any issue other than posibly slightly less oil pressure depening on the stacking clearance.

So as stated, you can look at switching bearings to get to the clearance you are looking for. You can usually swap bearings around to get the number you are looking for.