Dart SHP Cam bearing failure

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Dart SHP Cam bearing failure

Post by Racer18 » Wed Oct 11, 2017 3:57 pm

Anyone else seeing #4 cam bearings melted? The other 4 look fine. This has been in every SHP block we have worked on in the last year, some built by us, some not. We use the Durabond DT1T bearings, don't know if there is a better choice out there or not. As a side note- none of them spun in the block, or had oil pressure issues, just melted the bearings on the bottom side. On #4 only.

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Re: Dart SHP Cam bearing failure

Post by MELWAY » Wed Oct 11, 2017 9:15 pm

Is this a potential cam bore alignment issue.
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Re: Dart SHP Cam bearing failure

Post by 1989TransAm » Wed Oct 11, 2017 9:25 pm

Mine Dart SHP block serial number is just over 400 and has been running fine with no problems. I am only running around .600" lift with a Jones 233/233 camshaft.

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Re: Dart SHP Cam bearing failure

Post by claysmoker » Wed Oct 11, 2017 11:12 pm

What does Dart say about it?

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Re: Dart SHP Cam bearing failure

Post by Racer18 » Thu Oct 12, 2017 6:40 am

Dart says they have never had any problems in that area.

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Re: Dart SHP Cam bearing failure

Post by mag2555 » Thu Oct 12, 2017 8:21 am

Without more detail one would have to assume that your running a steel Cam with spring pressures enough to bend or whip the Cam around in that location as the first 4 Cam bearings are the same part number, no?

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Re: Dart SHP Cam bearing failure

Post by Racer18 » Thu Oct 12, 2017 9:39 am

All the bearings are the same part number. We are seeing the same bearing failures with roller cams with 650# open pressure, as well as flat tappet cast cam cores with 385# open. My first thought was spring pressure, but the last one proves that wrong.

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Re: Dart SHP Cam bearing failure

Post by mag2555 » Thu Oct 12, 2017 10:22 am

These Cam journals show no bluing ?
A problem with a restriction in Cam oil feed hole up from the main?

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Re: Dart SHP Cam bearing failure

Post by Racer18 » Thu Oct 12, 2017 11:17 am

No, cams look perfect! Oil clearances are wthin .0002 front to back. Once again, this has occured on several engines, all using Dart SHP blocks. As a matter of fact, every single one we have taken apart since Jan. They have no oil pressure problems, no indications other than the #4 bearings (cam) are melted

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Re: Dart SHP Cam bearing failure

Post by mag2555 » Thu Oct 12, 2017 11:28 am

The only thing that I could even remotely imagine going on block wise for only the lower part of the bearing to be going south would be the Crank running loads on the main web are pinching in on that area of the Cam bulk head, but then I would expect to see some kind of ware on the Cam!

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Re: Dart SHP Cam bearing failure

Post by Racer18 » Thu Oct 12, 2017 11:31 am

I suspect it has to do with the distance between the #4 & #5 cam bearings. Just have never seen this many all of the sudden, and never saw it with GM blocks over the last 30 years. #stumped

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Re: Dart SHP Cam bearing failure

Post by MadBill » Thu Oct 12, 2017 3:18 pm

Sounds more like an oil supply issue to me. Has the continuity of the relevant oil galleries been verified?
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Re: Dart SHP Cam bearing failure

Post by Racer18 » Thu Oct 12, 2017 4:05 pm

These blocks are widely varying in age and serial numbers, I think its highly unlikely to be an oil galley issue, but I dont know

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Re: Dart SHP Cam bearing failure

Post by Newold1 » Thu Oct 12, 2017 6:28 pm

My thinking would be that this is an oil delivery issue at the #4 bearing as the only thing that's going to melt that bearing and generate that much friction or heat has to be a dry bearing but it is odd that the #4 cam bearing journal is not showing a lot of visible damage and heat issues. Have you done an inside diameter measurement on all the first 4 cam bearing journals less bearings and then the same measurement with bearings on all 4 same cam journals? Are the bores round as measured with and without new bearings. Have the bores been checked for alignment front to back or have you determined align honing is not required? Have you measured the cam bearings themselves for differences before install, 1 to 4? How does this cam bearing set you are using as compared to lets say a standard CHP-8 Durabond bearing set?

One thing we all know here, there has to be a reason, it's just that most of us are stymied here from what you are finding and describing. :?

Another thought is do you have one of these Dart SHP blocks with serious other damage that might be sacrificed by putting it on a large band saw and sawing through those oil galleys that lead up to and feed the #4 journal?
If this is a casting or machining flaw in those Dart SHP blocks it's going to show up with that type of sectioning.

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Re: Dart SHP Cam bearing failure

Post by Racer18 » Thu Oct 12, 2017 6:50 pm

I just find it strange that no one else is having this problem!

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