Harmonic Balancer - super weird (at least to me)

[7900_Blazer]

1st crank - harmonic balancer 'barely' rubbing on the cross-member.

Back story... I purchased this '75 Blazer from a guy in Denver as a project with my 15 year-old. Supposedly a strong motor but needed tons of other work (we've replaced: both axles, bell housing, sm465, new quarters, rockers, inner and outer fenders, seats etc...), finally ready for a test drive.

1st crank and clearly something was rubbing - turns out it was the harmonic balancer rubbing against the cross-member. I don't remember it doing that when we drove it up on the trailer to haul to Texas - but there were so many 'other' noises that it very well could have been.

We've done nothing to the engine - thought maybe the new transfer case mounts were wrong but even loosening those and slightly jacking up the transmission/transfer doesn't allow for a piece of paper to slide between the harmonic balancer/cross-member below it.

I ordered a new 6 3/4 inch harmonic balancer (the one on the truck appears to be an 8")...

Any thoughts on this? Anyone ever have this happen?

 

[AyWoSch Motors]

1st crank - harmonic balancer 'barely' rubbing on the cross-member.

Back story... I purchased this '75 Blazer from a guy in Denver as a project with my 15 year-old. Supposedly a strong motor but needed tons of other work (we've replaced: both axles, bell housing, sm465, new quarters, rockers, inner and outer fenders, seats etc...), finally ready for a test drive.

1st crank and clearly something was rubbing - turns out it was the harmonic balancer rubbing against the cross-member. I don't remember it doing that when we drove it up on the trailer to haul to Texas - but there were so many 'other' noises that it very well could have been.

We've done nothing to the engine - thought maybe the new transfer case mounts were wrong but even loosening those and slightly jacking up the transmission/transfer doesn't allow for a piece of paper to slide between the harmonic balancer/cross-member below it.

I ordered a new 6 3/4 inch harmonic balancer (the one on the truck appears to be an 8")...

Any thoughts on this? Anyone ever have this happen?

I just recently put a 350 in my 78 k30.
It's down to the bare frame, so I put the engine in first, then the trans (th350), then the transfer (np203).
When the engine first went in, I had to jack the back of it up to mate with the trans, and it was tilted down so much that it hit crossmember. After I got everything in, with the brand new trans mounts, and old engine mounts, the balancer did scrape the crossmember a little bit, but after a few months of setting in, it doesn't touch it at all now.
It only has about a 1/8 inch or 3/16 inch of clearance, but it clears, and spins over by hand with now plugs. It seems like it was just a tight fit from factory.

I'd say wait a little while and see if the mounts settle in and squash down a bit.
A smaller balancer will definatly solve the issue too.

 

[Snoots]

You need new motor mounts.

 

[Grit dog]

^This.

 

[7900_Blazer]

So two responses that I need new motor mounts... Can anyone explain?

Are the mounts bad and require replacement vs switching harmonic balancers?

Thoughts?

 

[Itali83]

If you put new transfer case mount and have old hagged out motor mounts, it’s going to sit high in the rear and low in the front. Letting balancer touch crossmember. Putting new motor mounts will lift motor up in the front where it should be and gain you the clearance again. Not sure changing balancer to a different size all Willy nilly is the best idea.

ben.

 

[7900_Blazer]

If you put new transfer case mount and have old hagged out motor mounts, it’s going to sit high in the rear and low in the front. Letting balancer touch crossmember. Putting new motor mounts will lift motor up in the front where it should be and gain you the clearance again. Not sure changing balancer to a different size all Willy nilly is the best idea.

ben.

Is this typical for a 'bad' motor mount - rubbing on the cross-member?

How much of a pain is it to change the motor mounts? - on a scale of 1 to 10, with 10 being 'super painful'...???

 

[Snoots]

I depends on the tools you have available.

I'd just put a block of wood between the oil pan and floor jack, get some tension on it (don't try to lift the engine) and then one at a time, remove the old mounts and install your new ones.

 

[Grit dog]

So two responses that I need new motor mounts... Can anyone explain?

Are the mounts bad and require replacement vs switching harmonic balancers?

Thoughts?

Think about the mounts, rubber cushion, 20/40+ years of wear n tear on them, I bet they are soft or pooched a little.
Combined with the new mounts in the back raising the rear and pivoting the front down slightly.

Motor mounts are fairly easy, especially if you've already R&R'd the axles and half the body.

 

[7900_Blazer]

Think about the mounts, rubber cushion, 20/40+ years of wear n tear on them, I bet they are soft or pooched a little.
Combined with the new mounts in the back raising the rear and pivoting the front down slightly.

Motor mounts are fairly easy, especially if you've already R&R'd the axles and half the body.

Thanks for the encouragement... another unexpected 'wrench in the works' so to speak but just got to lean into it...

 

[7900_Blazer]

Took about an hour to change them both. Solved the problem!

Here are pics of the old ones.

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[AyWoSch Motors]

Yup, definatly the motor mounts. Those are pretty worn out When you do new mounts, you should do them all around.
Glad that fixed it.
They're relatively easy to change out.

 

[7900_Blazer]

@Grit dog and @Snoots nailed it!

 

[Snoots]

@Grit dog and @Snoots nailed it!

I do thank you and am glad that across the miles, and no pictures, the SWAG method and my experience from the same thing happening to me, the suggestion from myself and @Grit dog worked.

But YOU did the work. Give yourself a good 'attaboy' pat on the back and WELCOME to GMSB!!!

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[shiftpro]

Sometimes the rubber dries up and becomes really messy black powder. Other times they shrink.. or they just 'pack down'.

Countless problems arise over shot rubbers (including unwanted children but that's another story)... and often it's the last thing we look at.