Hi guys,

I have a GMC Syclone with a blown engine (hydrolocked = cracked block) so I wanted to drop a newer 4.3 vortec motor into the truck to get it back on the road.

I bought a 1999 Blazer engine here in the UK from an unscrupulous breaker and the engine had a lot of damage to it so I decided to do a full rebuild.

One of the problems I have is that the available cam bearings don't seem to fit properly. I have found by process of elimination that it is a T type block but the #3 bearing is too thick. The cam will not pass through the block and the thickness of the #3 bearing is .0644 from Clevite but the existing shell was .0600.

Max Housing Bore=2.0010"
Min Housing Bore=1.9990"
Max Shaft Diameter=1.8692"
Min Shaft Dia=1.8682"
Max Oil Clearance=.0043"
Max Wall Thickness=.0644"
Overall Length=.7400"

The bearings that I have tried to install are SH1351S.

The cam that came out of the engine measures up to the specs given in the Sealed Power/ Federal Mogul / Clevite data sheets in terms of max shaft diameter so I think it is a stock sized cam (I'll get back to the cam in a second) but it appears that the cam shells are a little too thick to fit the cam into the engine.

Please can someone tell me where I am going wrong?

As for the cam, it had a QR code on the front of the cam which made me think it might be aftermarket but it also had a number on the side of it - 691 GMPT BC 20 which makes me think it is standard. GM part?

On the same face as the QR code was the same number but with a bit more detail:

691
20F
8264

The above seemed machine stamped but "A10" was stamped over the top of the above numbers. Wish I took a pic.

Any ideas? Thanks for looking and Happy New Year!

Mark

 

Theres different cam bearings for these engines,it depends on what block you have a w or z block.You need to look at the front pad on passengers side head and read that code.Its been while since I didnt mine so I can remember what sequence in the code where the w or z is.
Maybe someone else can chime in give you more descriptive info.

 

Thanks - I was aware about the difference between the Tonawanda blocks and the Romulus but not the W and X variations. The Tonawanda blocks had a different arrangement for the cam bearings and the first kit I ordered was definitely wrong but according to the Clevite manual, the SH1351S kit is correct.

The main problem seems to be the thickness of the bearings. The bearings all fit but the bearing that came out of the truck is .0600 whereas the replacement bearings are .0644, a considerable difference.

The truck was a 4WD so I am guessing that the block is a W block. The stamp on the machined surface had nothing on it. The engine was bought used.

I have read that people have been known to have to ream out the bearings to make the cam fit.

Cam Bearing And Installation - Rod & Custom Magazine

Can anyone else chime in?

 

Ream out cam bearings NO FN way!Remeve the bearings from your engine if you havent all ready and match them up.I know on one set the 2 middle bearings are thicker.On the other set all of them are the same size except for the either the 1st or last one.

 

Yeah, I don't want to ream anything out. I asked the shop to remove the bearings from the block and measure the housing diameter but the problem is the bearing thickness.

#3 that was removed is .0600 - I saw him measure it in the shop with digital calipers.

The smallest diameter in the bearing kit (both varieties) is .0644 - still too thick.

Have I got some kind of mutant block? I checked and marine blocks use the same kit.

This block is cursed. It had 2 melted pistons (2 and 3 - could the knock have worn the cam bearings down a bit?), two cracked heads, the block slipped in the machine shop and needed a sleeve, and now this cam issue.

FML.

Thanks for looking.

Any ideas on the cam? Is it aftermarket or stock?