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Discussion Starter · #1 ·
I have a 349 cube SBF with TFS R heads, 94mm turbo, and the usual internals for a combo like this: R302 block, BME aluminum rods, Diamond pistons, triple springs, shaft mount rockers, titanium retainers, titanuim intake valves, etc., etc.

My question is this: could the tension on a belt drive be to much for a Durabond type cam bearing? Also, assuming you have adequate oiling, would you say there is a point at which you can have too much valve spring pressure for a Durabond type bearing? Or could the combination of the two cause a Durabond type (non-roller) cam bearing to fail quickly after initial start up of a new engine? (i.e. less than two hours run time and no passes). Keep in mind this engine had everything in it brand new with all fresh machine work, and it was pre-lubed before start up for a full 5 minutes with a 1/2" drive 110 volt drill before firing.

My reason for asking is we have another engine of basically the exact same combo (same heads, same springs, same cam, same oiling system, etc.) and never had an issue (yet ... knock on wood). This one didn't make it off the dyno before it ate the front three cam bearings and the rear two spun forward out of the block.

Anyone ever hear of this happening? Mine is going back together with roller bearings due to damage to the block, but I'd like to think the roller bearings will be able to handle the extreme valve spring pressure and the loading the belt tensioner on the Danny Bee puts on the front cam bearings in particular.

I was pretty bummed out with the fact it happened to a brand new engine with only chassis dyno time on it, but the main thing is, I want be able to feel like roller cam bearings will solve the problem once and for all. However, with our other car having quite a few passed on it without any issues, I'm not feeling very confident.

Thoughts? experiences? comments? suggestions?
 

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:confused: DAMN!! sounds like an oiling problem!! we run 400llbs on the seat, durabond bearing in an aluminum sbf,, with no issues.. do you have oil restictors for the cam bearings? also run a belt drive..vac. pump,wet sump oil system..etc. may be a freak deal??:cool:
 

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Collecting dust
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Discussion Starter · #4 ·
check the cam for straightness if there are no oiling/clearance problems
No way to tell. The front three cam bearings were completely destroyed, and the two rear ones spun forward out of the journals. The cam got into the block and the cam is damaged beyond repair. The block had to be machined for roller cam bearings to repair it. I just seems a bit odd considering the same block had been run with the same valve spring pressure (but with a timing chain rather than the brand new Danny Bee), and with more cam than this last year with no problems. The engine builder is fixing it, but it happened back in first week of June. I've basically missed the whole race season, so it's just frustrating with a new car and not being able to run it all Summer. Oh well, I've been through worse. At least they are makng it right. I can't complain about that. :smt023
 

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Sound like bearing install issue.
 

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i don't know much about ford engines but i had a buddy who was spinning bearings in a chevy and he had the wrong part # bearings installed. double check you have the right stuff.
 

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I have used the Durabond cam bearings many times in my SBF engines. I have run as much as 380 lbs. on the seat and 950 lbs. open with no cam bearing failures. I have run a timing chain and a belt. I can't see the belt being the problem. If the new cam was straight, and clearences correct, I am thinking it was more of an oiling issue. Did the motor have restrictors in it? My new SBF engine has 55 mm roller cam bearings in it. I know you will like the roller cam bearings better.
 

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Discussion Starter · #10 ·
I have used the Durabond cam bearings many times in my SBF engines. I have run as much as 380 lbs. on the seat and 950 lbs. open with no cam bearing failures. I have run a timing chain and a belt. I can't see the belt being the problem. If the new cam was straight, and clearences correct, I am thinking it was more of an oiling issue. Did the motor have restrictors in it? My new SBF engine has 55 mm roller cam bearings in it. I know you will like the roller cam bearings better.
You sound as though you have a VERY similar spring to mine. The block did not have restrictors that I am aware of, but then again, that's why I paid someone else to build it, so I can't say for sure and I've not asked that question.

I've got the engine back now and got it back in the car and had some dyno tuning and made 4 passes on the car last Wed. night. I couldn't be happier. Literally every nut, bolt, and part of both the front and rear suspension is new/different than before, so it is all at ground zero on set up, but the engine ran flawlessly. The roller cam bearings seem to be great. :smt023
 

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:confused: DAMN!! sounds like an oiling problem!! we run 400llbs on the seat, durabond bearing in an aluminum sbf,, with no issues.. do you have oil restictors for the cam bearings? also run a belt drive..vac. pump,wet sump oil system..etc. may be a freak deal??:cool:
What lifters are you running with 400lbs on the seat?
 

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I have used the Durabond cam bearings many times in my SBF engines. I have run as much as 380 lbs. on the seat and 950 lbs. open with no cam bearing failures. I have run a timing chain and a belt. I can't see the belt being the problem. If the new cam was straight, and clearences correct, I am thinking it was more of an oiling issue. Did the motor have restrictors in it? My new SBF engine has 55 mm roller cam bearings in it. I know you will like the roller cam bearings better.
What lifters are you running? Thanks!
 

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crane .875 solid rollers nothing super special, we change them every season. with no failures yet, about every 150 passes, rings, bearings, rods, lifters, gaskets. change springs along the way as they go bad or get weak.:cool:
 

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using a harder bearing / more durable rather than plain babbitt cam bearings allways helps.

every once in a while we have had to put in a screw to hold the cam insert bearing so that it did not spin.
in fact, even many of the roller bearing setups come this way from the block maker.

we often run 325 / 350 pounds on the seat and easily 900 / 1000 pounds open pressure with no issues.
oil clearance and FREE SPINNING OF CAM, along with proper original press fit of insert is of PARAMOUNT IMPORTANCE.
if your original engine builder / assembler did not allready know about this, then you should then also know that he aint done gone down this road before. maybe you should be looking for someone else.!!!
 

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The front three cam bearings were completely destroyed, and the two rear ones spun forward out of the journals.
Saw this one time with a local "cam grinder" who made a new bullet from a new billet. It was a roller with a lot of spring pressure, BBC. The bearing journals were only turned and not ground or polished afterward. The tool-marks were a fine thread that screwed the bearing inserts out of the housing bores in the block. You could drag a finger nail across the bearing journal and file off nail material on the tool marks.

Genius cam grinder and genius engine builder and neither one took responsibility, blaming it on each other.
 

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If I remember right, on sbf, each cam bearing is a different size, and so are the cam journals. They have an order they're installed in. I'm wondering if somebody didn't get them in in the wrong place, causing the issue.
 

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well,
anything is possible.

but since the cam bearings are each at least ten to fifteen thousandths different in outside diameter, it would be pretty difficult for the wrong insert to be installed into each housing bore.

and someone said that they THEN installed roller bearings in the block.
well, since HALF of the original inserts are larger than 55 millimeters, then what was actually done???
and if they did in fact do this allready, then I also hope that the cam has HARD BEARING JOURNALS.
or at least a hard sleeve installed over the original bearing journals of the camshaft core.

I use the stronger SH-1321S cam bearing inserts in a standard / common / stock cam bearing tunnel bore in the block.
if the block has been changed to the more common RACE type setup with all the same diameter ( 2.080" journals), and 2.204" housing bore diameter then bearing insert # SH-1763 can be fitted.

in all cases, I install a locking screw.
 
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