I'm just starting to assemble my project motor and I have a problem that the cam won't slide all the way into place. I've narrowed the problem down to the rear cam bearing being too tight. Measuring the cam jurnals and the ID of the bearings I get this:
1 Journal 1.999" bearing ID 2.001"
2 Journal 1.983" bearing ID 1.985"
3 Journal 1.970" bearing ID 1.968"
4 Journal 1.952" bearing ID 1.950"
I've got .002" clearance on 1,2 &3 but a .002" interference on #4
What I don't know, do I have a cam problem or a bearing problem?

_________________
--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

Well, I've determined that the cam is not at fault. I have 2 old stock cams here and they both measure 1.952" at the rear journal.

Assuming I need to have .001" or .002" for oil clearance my new bearing is .003"-.004" smaller on the ID than it should be.

Anybody have a suggestion?

_________________
--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

Your machinist should have been provided with the cam to compare to the bearing when you dropped the block off for machining...if it's too tight, he can "scrape it" to put it in tolerance...

.003" - That's a lot of scraping.
I could see scraping if it was a matter of being slightly out of alignment - which is what I thought at first. I started out marking it with dykem and scraping where it was showing no clearance. It didn't take long to realize that it was more than some little misalignment causing my problem.
I guess I could get a new bearing and turn the ID in the lathe if necessary.

_________________
--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

I don't know if this has ever been a problem with the slant six, but some B/RB motors had a problem with th rear cam bearing bore in the block being undersize. The factory used a bearing sized to fit (either made with a smaller OD or used an unfinished bearing, installed it, then sized it, don't know which). When rebuilding these engines, we had the machine shop correct the bearing bore to the correct size. Then a standard bearing could be used. Might want to check the bearing bore dia.

_________________
Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I'd love to check that but I have not been able to find a spec for what the bore ID should be.
Anybody know?

_________________
--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

#4 cam bore @ 2.080 to 2.081
DD

Thanks DD!
I'll get a fresh bearing and measure the bore.

_________________
--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

Are all 4 holes the same?
Or is the bore in the block different for each bearing?

With #4 bearing removed the cam is also slightly tight in #2 and #3.
Perhaps that is some bit of misalignment. I'll check with Dykem.
#1 feels just right if I slip the cam into it backwards.

_________________
--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

Here's at least part of the problem. The quality of the cam bearing bore is lousy.
Chrysler ran the boring tool through so fast it looks (and feels) almost like a threaded hole.



When I put the bore gauge in and the contact points settle into the 'valleys' it measures right on the money at 2.080"



If I wiggle the bore gauge around and get the contact points up onto the peaks it measures almost .0015" tight.


My newest question:
Do I hone the bores or do I rework a set of bearings?

_________________
--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

I'm wondering if that is exactly what was mentioned about the big blocks. Could you hone that down to spec and be good to go, or is it to much material?

I can hone it. Before I get started on that I will need specs for all 4 bearing bores so I can make sure they are all spot on.

_________________
--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

We had the same problem when we assembled Ryan's Dart 10 years ago. I had never heard of scraping the bearings but we took it back to the shop that installed them and they scraped them and they ran for 10 years and 50,000+ miles of hard abuse. They were not real pretty but no one can see them once they are in the car.

I'd probably be just as afraid of enlarging the bore too much as having the bearing scraped. But it looks like you have all the precision tools to get good measurements.

Rick

_________________
2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

Solved!
Pretty easy and didn't take too long.
And didn't require butchering the bearing with a machinists scraping knife.

I put the rear bearing back in. Then took an old junk camshaft I had sitting around and cut some angled slots in the journals. Actually cut 3 slots in each more or less evenly spaced. The slots are angled to make cutting edges.



I used the 'cutting tool' cam to scrape the bearings. It took quite a lot of turning the cam with plenty of oil. After scraping all the way through the bearings I spun it with a cordless drill for a while to get a little more cut for clearance.

The scraped bearings look great and are very smooth.


I've got .0005" clearance at the front and rear bearings. A little more at #2 and #3. The new Howard's Cam goes in easy and turns smoothly.

_________________
--> Check out my FI Turbo build <--
--> And the race truck build project <--
--> The Diesel Corvette <--

That is a slick solution.

I have used a brake cylinder hone to correct many thousandths of interference. Not the best way but it all ran good. (Fiat 124 Spider motor....)