[bammbam]

First off Happy Easter everyone

I'm about 95% done with my 67 GTO convertible restoration and decided to take it to a local show yesterday. Right before I arrived I started losing oil pressure, which it turns out the engine oil was no longer in the engine, it was all over the engine compartment. Long day getting a trailer to get the car back home. When we tried to crank the engine we noticed the HB pulleys wobbeling but didn't see anything obvious. Today I found the problem...the hub for the HB broke, see photos, so the big question is why and is it preventable??? it is/was an original hub. any one ever experience this?

seems that all the pieces are accounted for and the key is still in the crank so I don't think metal in the engine is a concern. any advice or guidance on what to check would be appreciated. I don't want to put another hub on and have the same thing in another 200 miles

[Half-Inch Stud]

That looks exactly like a loose balancer crack-out. As if the Balancer Bolt was not TQ'd enough. 160 Ft-Lb TQ will prevent the problem from occurring.

I experienced that, because I didn't TQ the Balancer Bolt after some sort of underhood project ~20 years ago.

[bammbam]

bolt was torqued to 160 ft-lbs during the engine build. Had a heck of a time getting it off without a good way to stop the engine from turning

[screamingchief]

Hmmm,lemme take a WAG here (after looking at those pics).

Your timing chain set has a crank sproket w/three keyways so it can be installed +/0/- .

Look where those cracks started,they're at three points virtually equidistant from each other.

If there were some burrs on that crank gear where the 3 keyways are,they could've easily created some stress risers there on the hub when the balancer bolt was torqued to the 160 lb/ft spec.

At the very minimum,I would wanna inspect that lower (crank) timing gear very closely.

FWIW

Bret P.

[bammbam]

It looks like the key may be out of the groove on the crank so the back of the key is high, front of the key is low, I was using a mirror and a flashlight and didn't get a real good look at it yet, need to roll the engine over a little bit. If it is not properly seated I would suspect that happened after the fracture. if the key was real tight in the groove, and not seated I could see that leading to failure, one of the fractures is at the key way

does the hub bottom out against the timing gear?

[bammbam]

screamingchief, that's a pretty keen observation, you are right they are almost exactly equidistant, and there is a small polished spot at one of the cracks. also the face isn't perfectly smooth, has multiple dings and "bruises"

[screamingchief]

Originally Posted by bammbam

does the hub bottom out against the timing gear?

Yes it does.

No matter what,I'd pull the timing cover so everything could get a very close inspection.

I'd also make sure the cam gear and fuel pump eccentric all got assembled properly so that there is the correct cam endplay (.003" to .007") as I could easily see that (too much cam endplay) being a contributing factor on a deal like this as well.

Also I'd wanna check out the timing chain set closely as a whole to make sure it's OK,and I'd check that bottom gear with a magnifying glass or such for imperfections at those keyway(s).

I'd also mic the OD of the snout on the crank as well,and mic the ID of the next hub and the lower timing gear,if there is too much clearance there,that also would explain alot as well.

For sure your gonna need a new timing cover seal,so IMO the cover needs to come off.

HTH

Bret P.

[bammbam]

I was hoping I could leave the timing cover on but have conceded to the fact it's coming off. I planned to install the new hub with the cover off and torque it down, then remove it for inspection and check the faces of the hub and gear for contact. I'll take car of the other inspections too and see what's up. I want to make sure there are no burrs catching the key too. Will post some more pictures when I get the cover off.

[Rugratman]

On another note.....That really sucks.

[Half-Inch Stud]

ALSO, I'm not familiar with that Balancer: appears to be a solid 1-piece, without Dampener runner& ring.

[Pontirag]

Take a very close look at that crank sproket too!Polishing means mooving. that it should not Do.

[lust4speed]

When you installed the crank hub, did it slide all the way on with hand pressure and bottom out, or did it have to be tightened with the bolt to pull it in?

[Tom Vaught]

Crank "HUB" is Not a harmonic balancer. Why Pontiac ever did something like that escapes me.

You need a REAL harmonic balancer your next time around. They are cheap enough that no reason not to buy a Pioneer or similar one.
Torqued properly, It will save the rest of your crank/engine parts.

Tom Vaught

[chiphead]

I agree with Tom 100%. The '68-newer balancer is much better for actually dampening crank harmonics. However, millions of '67-earlier engines were built with that crank hub and lived long lives. The only real way to convert this motor over is to run the '68-only timing cover that allowed the use of the later balancer and 8-bolt water pump and '67 P/S pump. The aggravation of finding a set of '68 crank and W/P pulleys may not be worth it to Mr Flintstone.

I converted my '67 engine to the '68 setup, as I wring mine at the track often and need the more modern dampener.

The easiest thing to do may be to find a quality replacement '67 crank hub assembly and make sure it fits the crank snout and bottoms on the timing gear properly. I'd also check the fastener, washer and crank key. If it breaks again, the motor is really trying to tell you something.

[performerrpm]

x-2 about the mic on the crank snout, hopefully since you say the balancer was torqed and something else caused it to break that maybee when it broke it did it all at once, and didnt actually wobble on the crankl any before breaking apart.


i had my balancer on/off a couple times, and i assume that somehow i thought i had re torqed it but didnt and with only running my 455 5 miles it cracked before i noticed it........long story short, my crank had to come back out and be welded back up because the loose balancer, once they crack they start wearing the snout down pretty quick

[lust4speed]

Either hub is going to fail if the assembly isn't correct. I ran the same early balancer on the street and on the track for over 24 years without any problems - and shift points were 6,500 during that time. Then I finally had a tech bust me a couple of years ago, and I had to go to the SFI unit which is only available in the newer style. I already had the electric fan, and I added the electric water pump and dropped the alternator down low, which avoided the pulley problem. I still have 5 Pontiac's running the early style balancer without a problem.

[Tom Vaught]

The 68-up balancers are a integral design harmonic balancer.

The earlier "balancers" were a bolt on design. As long as everything is tight the "balancer" does ok. I am referring to the 6 bolts, not the 160 lb/ft bolt.

I have seen my share of early "balancers" fail.

Unless the late model harmonic balancer was built wrong, or some of the chinese aftermarket crap, rarely do you see one of the late model ones fail.

Tom Vaught

[bammbam]

Thanks for all the support, just to clarify, this is the early 2 piece balancer, the piece with the rubber insert bolts to the hub that cracked.

I got the timing cover off tonight and the only thing I find suspect is the face of the lower timing gear. there is a burr about 0.006" high at the key slot and the face isn't what I'd call a machined surface and isn't exactly flat. the replacement hub rocks very slightly when face to face with the timing gear. I suspect some of the damage may have occurred after the hub cracked. Looks like it was beat on lightly with a ball peen hammer.

clearance between the snout and the bores of the gear and replacement hub seems to be in the 0.001-0.002 range. they both slide on the snout with out too much effort and that was also the case with the one that broke. My internal mic isn't that small so I had to use a telescoping gauge and calipers. The snout doesn't show any damage and miced the same in several places, 1.374"

[bammbam]

here is some pictures of the crank snout and gear. Forward plan: I have a NOS timing set to install. The hub sets flush with no rocking on the timing gear. there is a little rocking between the hub and the timing gear I removed.

1) make sure all the mating surfaces are flush with no rocking between the parts.
2) mic the OD of the hub for reference
3) assemble the lower timing gear and hub with a new key
4) Torque the crank bolt to 160 ft-lbs
5) mic the OD of the hub to check for any distortion
6) if everything checks out remove and then install the timing cover

also need to check the cam end play along the way.

If anyone has any steps to add please chime in.

[bammbam]

Originally Posted by lust4speed

When you installed the crank hub, did it slide all the way on with hand pressure and bottom out, or did it have to be tightened with the bolt to pull it in?

slipped right on, in fact I wondered if it was supposed to be that easy???? any modern balancers I messed with had to come off with a puller