Shaft Diameter

[gramps]

Harmonic Balancer shaft diameter 400 sbc?

[Kevin Johnson]

Bore diameter below:

http://www.crankshaftcoalition.com/wiki ... nd_install

550px-Measuring_points_damper_-_keyway.jpg

750px-Crank_snout_-_keyway_dimensions.jpg

[Dan Timberlake]

Some of the non-Chevy GMs had slip fit dampers. I forget if B, O, or P.

This suggests Pontiacs were slip fit, at least in 1957.
http://pontiac.oldcarmanualproject.com/ ... age17.html

This suggests Olds crank to damper fit is 0.001" tight to 0.0007" loose, at least in 1976
http://www.oldcarmanualproject.com/manu ... ge448.html

Slip fit dampers generally have real high bolt torque specs to restrain the damper by friction from axial clamping. And they need it.

[Jeff Lee]

My "professionally built" AMC race engine lost all bearings at 30 passes and about a dozen dyno pulls. Do to "this and that" I assumed it was oil pump cavitation. I am now rebuilding the engine and discovered the ATI balancer to crank post clearance was .012". I contacted ATI and found that even a new hub would allow .0055" clearance and ATI recommends .001" to .0015" clearance. Not sure what the old shop did to the post of the crank ( I assume they turned or polished it for some reason) but it's fairly obvious they honed the damper hub excessively.
I just got the crank back from Shaftech the other day. They did a beautiful job of welding up one rod pin that was damaged along with building up the post to properly fit the damper which I had also sent to them.
Now I should have better engine life now that the damper will actually work. And to be safer, I also am adding a MasterLube accusump.

[SupStk]

Snout diameter will vary between an OEM crank and many aftermarket ones.

[roc]

Snout diameter will vary between an OEM crank and many aftermarket ones.

That's a very good point. I was surprised when I found this out. I wonder why they do that.

[SupStk]

Snout diameter will vary between an OEM crank and many aftermarket ones.

That's a very good point. I was surprised when I found this out. I wonder why they do that.

Guess I'm not sure why but I'd imagine it's so a builder could selective fit whatever damper they choose.

[pdq67]

One thing that has interested me is that the old 348/409, (and I assume), /427 "W" engines have small block crank snouts!

pdq67

[jsgarage]

Supstk is right. Romack Dampers told me they have a special part number for cranks from SCAT (any engine) because the noses are so consistently undersized. The damper white paper says a damper should always be an interference fit (maybe 0.0005") and shops that hone them out are simply making installation easier but wrecking the way it was supposed to work. I feel sorry for the BBC guys with factory unthreaded crank noses, though.

[pdq67]

jsgarage,

I didn't know that some "W" and BBC cranks were undrilled and tapped from the factory.

Please tell more, like what engines and years..

Thanks.

[kirkwoodken]

If someone somehow garffed up the inside of their stock balancer, maybe making a crank snout .0015 larger will allow them to use it with a freshly honed hole the right size. Mike Lewis told me my new damper would need to be honed for my new scat snout. No problem. I think the larger size is a good idea.

[jsgarage]

A friend had a bought-new 427 Chevelle-1970 I think. Going home from work one night, the balancer flew off, hit the radiator punching a hole, then bounced once off the highway and landed on a 911's front hood breaking the windshield. When he got home (slowly- no water pump or alt either since the belts were also gone) he noticed no bolt. After pulling the rad, no threads visible in the crank nose either. VERY expensive fix if you include the court case brought by the Porsche owner for damages.

[Dan Timberlake]

This seems to suggest all W motors used pressed on dampers, and no torque, so no damper bolt.
http://www.tpocr.com/chevrts.html

The venerable "How to Hot Rod Big-block CHEVYs H.P. Book only talks about installing dampers with the tapped crank snout.
My copy is dated 1971.

[pdq67]

My '67, 350SS engine had a bolt and a big thick washer, but it was interference fit too.

pdq67

[member-83854792]

Hey Jeff Lee.
I have seen this problem on dirt engines where the balancer is loose on the snout causing excessive high frequaency vibrations and destroying the main bearings. I even seen one racer remove the outer inertia ring for reduced rotating inertia. 5 laps into The race the front 3 mains pulled out of the block.
The early (pre 1968) small journal chevy 283 AND 327 were not drilled and tapped from the factory. This is called a press fit or interference fit in machinist terms. We usually allow .001" to .0015" per inch of diameter.
We must realize the balancer absorbs vibrations and changes this energy to heat. If there is no conduction, then the balancer cannot keep the front of the crankshaft cool and can hurt it. Have you ever measured the temp of a balancer on a dirt track engine?