Author Topic: 50mm roller cam bearings ?  (Read 546 times)

Offline denverflatheader

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50mm roller cam bearings ?
« on: July 01, 2017, 10:25:41 AM »
Anyone have recommendations on when to select 50mm roller cam bearings versus stock sbc cam bearings?  Have been collecting parts the past year to build a Kinsler injected sbc with symmetrical port Dart/Buick 10 degree heads.

Cam specs are:
General Kinetics "Special CR-308/312-10R:  309/313 @.018" - 272/276 @.050" - .188/190 @.200" - 420"/.420" cam lobe lift - 110 Separation; 108 Intake lobe center-line.

Just bought this 50mm roller cam bearing camshaft.  50mm roller bearings I.D. are 1.875, stock sbc cam bearings I.D. are 1.868.  My aluminum sbc is setup with stock cam bearings.

Wondering which is better route, grind 50mm roller cam journals down to fit stock sbc cam bearings, or modify stock block cam placement to install 50mm roller bearing, or other ideas.  Alan

p.s.  All aluminum engine will replace stocker in my old stingray which hasnt moved in 30 plus years.  Be a street/track car may see 7-8000 rpms.

Offline dreracecar

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Re: 50mm roller cam bearings ?
« Reply #1 on: July 01, 2017, 12:52:13 PM »
If you are haveing bottom oil issues you can direct more oil to that area because the rollers live on splash.
Rollers walk around in the bores and have to be pinned in place, New Sprint car blocks have holes machined in the valley to do this , older blocks have set screws tapped into the cam bores both side of the bearings.
 For the 7 seconds we run, I dont see the need/results that warrant the expense

Offline denverflatheader

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Re: 50mm roller cam bearings ?
« Reply #2 on: July 01, 2017, 03:58:34 PM »
dreracecar - appreciate comment.  Not expecting bottom end oil issues.  Alan 

Offline dusterdave173

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Re: 50mm roller cam bearings ?
« Reply #3 on: July 02, 2017, 05:38:50 AM »
Check to see --if you grind down journals will lobes pass through std bearing diameter--some will some will NOT--I would go std bearing if possible to save that $loot   cheap to have crank grinder do the cam
I have always had a fascination with fast cars at the expense of more normal character development

Offline denverflatheader

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Re: 50mm roller cam bearings ?
« Reply #4 on: July 02, 2017, 12:32:34 PM »
dusterdave173 - thanks for likely conflict to check.  Should have cam within 2 weeks, will verify if its a clash to install.  Alan

Offline JrFuel Hayden

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  • Your Best Time: 6.02, 236 mph, 1/4 in 1973 Div 3 TF Champ
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Re: 50mm roller cam bearings ?
« Reply #5 on: July 02, 2017, 12:43:59 PM »
Do you have Alum rods ?
When cam grinds came up with larger base circle cams for better lobe shape [ ie, lifter launching on the back side] stanadrd blocks and designs , started hitting the cam with alum rods, especially big rod end rods.
 My first JF iron SBC [ bow tie] that I bought from Art Chrisman, he had to have Crane cams grind a SMALLER than OE base circle cam to get enough clearance.
That's why when I built my first SBC, I bought a raised cam block from Dart so I could run the better 55mm cam.
BTW, you don't have to run the roller bearing cam bearings, YA engine builders like them because it turns over easier, but with good oil pressure the cam rolls over as easy as the roller bearings.
Either way you may have to line bore your cam journals larger for you 50mm cam , even with non-roller bearings.
I have heard of some racers having problems with the cam roller bearings moving, but I think thats because they were running super light cranks [ 32 lbs] and the crank was flexing and maybe causing some block flexing. They had to pin the cam bearings.
 I never had cam bearing movements in 10 years, of 10k rpm use.
Talking about cams, when a few of our JF racers went with high 8" to 9" valve lift they had some oiling problems, such as no oil going up the push rods, and of course no oil in the rockers, because when using OE style lifter bores, the lifters would lift past the oil passages for the lifters. Matter-a-fact Bob McKray trying to firgure the oil problem, he turned the oil pump over [ on an engine stand] with out the oil pan, and said the oil came out from the cam valley "like a garden hose, so the fix was bore out the lifter bores and install base busings. I never had this problem because I use Jesel Keyway lifters, again for 10 years.
So check your rod to cam clearance before to proceed.
Jon C. Hansen

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Offline denverflatheader

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Re: 50mm roller cam bearings ?
« Reply #6 on: July 02, 2017, 01:27:27 PM »
Jon thanks for detailed information.  Not using aluminum rods, have 6 inch steel I-beam rods, so probably no conflict.  Have 2 crank options, a Keith Black 3.48 or a Moldex 4.00.   Neither crank is super light weight : ) have to guess no flexing with either billet crank.  With my starting rocker ratio, will be closer to .660-.670.  8-9 valve lift for you JrFueler guys much beyond my needs for this engine's purpose.  Im going with Morel lifters, and will check and check again for oil problems. 

Had lunch with a friend of mine 2 weeks ago, John M. who races with your group with a new Parks car told me how much you do for making that JrFuel Association so successful at your races.  He spoke highly of your drive!  Alan

Offline JrFuel Hayden

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Re: 50mm roller cam bearings ?
« Reply #7 on: July 02, 2017, 03:04:25 PM »
Thanks for the John report, I'll be watching on DragRaceComp.com for results on John racing at the NHRA National race in Denver, while I'm racing in Sonoma in our Div 7 race in Comp elim, running B/ND.
Jon C. Hansen

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