[Stan65]

Hello all,

My number 4 cam journal measures 2.0364, roughly .005 over. It is also concentric +/- .0001. The original GM bearings fit when I knocked them out. Wish I would have saved them to measure, but didn’t think anything of it at the time. The bore looks like all the rest other thin different ID’s. It also doesn’t appear the bearing had spun.

All the other bores checked out ok.

I haven’t been able to find a partial or full set of P4R1 Durabond +.010 OD bearings. I want to use the block as its number's matching to the car.

The new bearings (P4 Durabonds) are a slip fit in the bore for #4. The new bearings OD’s all measure within spec for new bearings.

I just don’t feel fuzzy about Bearing Retaining Loctite.

Have read about nickel plating the bearings to increase OD. This may be my only hope other than figuring out how to bore #4 in the block and sleeve the hole.

Anyone have any ideas or suggestions?

Thanks,
Any help is appreciated.
Stan

[steve25]

While I like the idea of plating the OD of a bearing I fear the effect of Hydrogen embrittlement on the steel backing could case a failure pretty quickly.

I hope you’re able to turn up over size bearings even though the whole process of using then will be expensive.

In fact just finding a shop that could do the needed machining might be difficult.

[Stan65]

I’m “hoping” to find at least 1 bearing.

If I can, my thoughts are grind the OD of the shell to the proper interference fit. Using proper tool post grinding process of course.

It will only require ~.0025 off the thickness of the shell.

Then, will need to check alignment.

Not gonna be easy, but I have to do it to save the block.

Next step will be a custom bearing shell. Then have it Babbitted.

Here’s an interesting read from Mahle. Last paragraph.

https://www.mahle-aftermarket.com/me...dfs/tb2078.pdf

[PAUL K]

We've pinned loose fitting cam bearings with a roll pin installed through the valley pan bolt hole.


The hole that is .005 too big, is there any press fit with a new bearing?

[Formulas]

https://metalspraysupplies.com/metal...t-is-arc-spray

possible to arc spray a bearing shell for exra thickness? says wood can be done

this is a process done to some aircraft......

how about powder coating the back side that can be a few thou thick and fairly hard

[Stan65]

Paul,

It is a slip fit. If I was making something that needs a precise slip fit I couldn’t do any better.

Formulas,

Interesting.

I can powder coat it. Also curious how that would hold up.

Was thinking the nickel plating would be as good as it gets. Haven’t read up on the hydrogen embrittlement thing yet.

[steve25]

After all this time you would think a process like the knurling done on valve guides and the skirts of pistols would be available for cam bores.

[Stan65]

Steve,

I actually looked into it. Doing either the block or the OD of the bearing shell.

I may try to make a mandrel to support a bearing and knurl it in my lathe. I have an extra set of bearings anyway.

Maybe use retaining loctite to help seal the oil passage way.

[Sirrotica]

You could knurlize the backside of the bearing to take up the space, then machine the OD to press fit in the bore. Many years ago, they knurlized piston skirts to make them fit cylinders that were oversized. it was a poor man's way to keep from boring the block and buying new pistons on daily drivers.

A good machine shop should have a knurling wheel to raise the OD of the bearing, then fit it to the oversized bore in the block.

If you wanted extra insurance against spinning, you could epoxy (JB Weld) it in the bore. JB Weld will withstand 500 degrees, so you're well within that on the backside of a cam bearing. The metal interference fit should hold it, but the epoxy would be extra insurance. The epoxy wouldn't transfer heat, but the metal-to-metal contact of the knurling should be enough area to remove heat to the block. Oil flow will also pull heat out of the bearing shell.

If I were trying to accomplish what you are, I'd certainly try it.

I see you were thinking the same thing I was while I was typing, and looking up the heat properties of JB Weld...............LOL

[grandam1979]

Did a quick search online looks like you can get .010 over bearings at different locations saw a set on eBay $65 free shipping plus a few other places. Butler has none available. Good luck with the block.

[Stan65]

Grandam1979,

I couldn’t find any in stock. If I click on the eBay link, it shows out of stock.

If you have a link to some In stock that would be fantastic!

Thanks,
Stan

[Dragncar]

You could use some Belzona epoxy That stuff is used to repair shafts that turn on babbit bearings all the time. Also used to repair large pump casings.
Far better than JB weld in my experience and I use both. You can not repair a gas tank with JB, you can with Belzona.

[steve25]

To add to keeping the bearing from spinning you could cut a shallow notch in the back side of the bearing then file a matching notch in the block and then make up aluminum key to drive in there with enough of a press fit to stay in the block yet not pinch in the bearing.

Also examine the web area around this cam Bearing carefully.
On a buddy’s Buick 455 he had a cam bearing that walked out some .

He thought it was just due to the cam being too tight.

He drove a new bearing in and did not think it went back in with much force,
then on the next tare down found that same bearing 3/4s of the way out.
Turns out the block was splitting in that web .

[grandam1979]

Your right sold out every place. I found this maybe, https://milkymotorsports.com/product...uZwdqZievqSND-

[Stan65]

Steve,

I saw that post. I had the block magnifluxed when we were doing all the machine work. Did see any issues then. After reading that post I went out and sprayed brake cleaner and used a magnifying glass and didn’t see anything.

The bore is almost perfectly round. I would think if it cracked it would get wider, but not affect height.

Grandam1979,

I’ll reach out and see what they have to say. I hadn’t looked for different iterations of the part number.

Thanks all!

[mgarblik]

I have some loose contacts at Durabond, so I called them for you. They currently have 13 back orders for DUR-P-4R1 bearings. Those are the .010" oversize bearings. They were waiting for 25 backorders to make the sets. I would think Butler would be in for 12 sets but don't want to bother calling them unless you want to go that route. That would require the cam tunnel to be line bored or honed +.010. Not a big deal if the shop has a mandrel the right size and a small enough dial bore gauge to measure them. Unfortunately, I do not have a mandrel that small at my shop or I would just do it for you. That would be the easiest fix though IMO to save the block without getting all exotic about it. Durabond said 4-6 weeks once the order threshold has been reached for the order. Let me know if you want to proceed in this direction. Good luck.

[Stan65]

mgarblik,

I appreciate you taking the time to do that leg work. I would be in for 3 sets if you can make it happen. 1 to mess up, 1 to install and 1 for the future if they are going to be that hard to source.

My local machine shop can bore the tunnel.

Thanks again,
Stuart “Stan” Landreth

[hurryinhoosier62]

Originally Posted by Formulas

https://metalspraysupplies.com/metal...t-is-arc-spray

possible to arc spray a bearing shell for exra thickness? says wood can be done

this is a process done to some aircraft......

how about powder coating the back side that can be a few thou thick and fairly hard

Spray welding is used in turbine engine components, not recip engine components. Oversize cam bores and main saddles are weld then machined back to standard in aircraft recip engines.

[hurryinhoosier62]

Originally Posted by Stan65

Hello all,

My number 4 cam journal measures 2.0364, roughly .005 over. It is also concentric +/- .0001. The original GM bearings fit when I knocked them out. Wish I would have saved them to measure, but didn’t think anything of it at the time. The bore looks like all the rest other thin different ID’s. It also doesn’t appear the bearing had spun.

All the other bores checked out ok.

I haven’t been able to find a partial or full set of P4R1 Durabond +.010 OD bearings. I want to use the block as its number's matching to the car.

The new bearings (P4 Durabonds) are a slip fit in the bore for #4. The new bearings OD’s all measure within spec for new bearings.

I just don’t feel fuzzy about Bearing Retaining Loctite.

Have read about nickel plating the bearings to increase OD. This may be my only hope other than figuring out how to bore #4 in the block and sleeve the hole.

Anyone have any ideas or suggestions?

Thanks,
Any help is appreciated.
Stan

Stan, at +.005 you have limited options. In my experience the best way would be to have this cam bore repaired with a repair sleeve then align bored back to standard. The problem with this is you need an engine machinist who has actually performed this operation. A repair sleeve would have to be machined, since no one manufactures cam bore repair sleeves for Pontiac cam bores. If you decide to go this route I have performed both operations many ( as in hundreds of times) times; I could talk a competent engine machinist through it. As Mike said earlier, your other option is to wait for Dura-Bond to produce sets of +.010 cam bearings and have all the cam bores machined to the proper size. Where are you located?

[mgarblik]

I will send an E-mail to David Butler and see if they are interested in bumping up the backorder with some additional stock orders. It's possible some of the 13 back orders are already theirs. That could complicate things some. Worth asking at least. I will get back when I hear from them.