| Slant Six Forum https://slantsix.org/forum/ |
|
| Rear cam bearing - too tight? https://slantsix.org/forum/viewtopic.php?t=57469 |
Page 1 of 2 |
| Author: | ProCycle [ Fri Apr 10, 2015 4:59 pm ] |
| Post subject: | Rear cam bearing - too tight? |
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? |
|
| Author: | ProCycle [ Fri Apr 10, 2015 6:00 pm ] |
| Post subject: | |
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? |
|
| Author: | DusterIdiot [ Fri Apr 10, 2015 7:03 pm ] |
| Post subject: | Machinist... |
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... |
|
| Author: | ProCycle [ Fri Apr 10, 2015 8:24 pm ] |
| Post subject: | |
.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. |
|
| Author: | Charrlie_S [ Sat Apr 11, 2015 4:05 am ] |
| Post subject: | |
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. |
|
| Author: | ProCycle [ Sat Apr 11, 2015 7:07 am ] |
| Post subject: | |
Quote: ...Might want to check the bearing bore dia.
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? |
|
| Author: | Doctor Dodge [ Sat Apr 11, 2015 8:44 am ] |
| Post subject: | |
#4 cam bore @ 2.080 to 2.081 DD |
|
| Author: | ProCycle [ Sat Apr 11, 2015 8:53 am ] |
| Post subject: | |
Thanks DD! I'll get a fresh bearing and measure the bore. |
|
| Author: | ProCycle [ Sat Apr 11, 2015 10:03 am ] |
| Post subject: | |
Quote: #4 cam bore @ 2.080 to 2.081
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. |
|
| Author: | ProCycle [ Sat Apr 11, 2015 10:24 am ] |
| Post subject: | |
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? |
|
| Author: | bboogieart [ Sat Apr 11, 2015 10:58 am ] |
| Post subject: | |
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? |
|
| Author: | ProCycle [ Sat Apr 11, 2015 11:05 am ] |
| Post subject: | |
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. |
|
| Author: | Rick Covalt [ Sat Apr 11, 2015 12:10 pm ] |
| Post subject: | |
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 |
|
| Author: | ProCycle [ Sat Apr 11, 2015 2:00 pm ] |
| Post subject: | |
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. 
|
|
| Author: | nm9stheham [ Sat Apr 11, 2015 3:45 pm ] |
| Post subject: | |
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....) |
|
| Page 1 of 2 | All times are UTC-08:00 |
| Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/ |
|