Main cap walk @ 2 & 3

[turbolc2]

From 1st hand experience,what is the cause of 2 or 3 main cap walk & subsequent block failure with a 6109 block?

 

[GNSCOTT]

friends experience.........Detonation

 

[Scott231]

Detonation. Plain and simple.

 

[Nick Micale]

If they are not installed properly, machined and fitted, they will move. This is a job for a pro who has done these, and has the proper machining tools.

 

[turbov6joe]

I also had #2 and #3 walk and thus warp from nothing other than detonation! It was SO bad, the billet main caps left metal transfers on the block surface Kinda looked as those someone was tapping the block surface with a welding rod... When the billet caps were removed, they looked like magnets/horseshoes in shape.

 

[turbojimmy]

So what's that sound like?

My subtle knock turned into a horrible banging and rattling sound Tuesday night. I drove it home 4 miles (20 MPH, flashers on) to stay out of the RPM range where the noise occurred. Sounds like mains to me.

I'm yanking the engine as soon as my new cherry picker gets here (I've had enough of my old one - leaks and the boom is about a foot too short - I'm on a simplify-my-life kick). I'm not sure what to look for, but something tells me it'll be obvious....

Now what? I've read in some other posts that mains for our cars aren't available from GM.

Jim

 

[Scott231]

If you are going to replace the main caps, you would be a fool to not use the billet steel caps. The front three will cost you $200. The factory rear main is so beefy, that it tends to not distort.

If your motor is making that much noise, you may have done more than spun one bearing

 

[GNXClone]

I wonder if adding a girdle and then pinning the caps to the girdle would help?

 

[Scott231]

No need to pin the girdle to the caps, the main studs take care of that. But if you want one of the toughest bottom ends you can get, use both the billet dteel main caps and a girdle. That is what I am doing this year.

 

[QuickWrench]

Scott, if unrepairable damage to a block occurs after having billet main caps and a girdle installed, can the caps then be transferred onto another block? Or is there too much material removed from the bottom of the caps when originally prepping them for the align-hone? This could make the cap sit too far down into the block for the girdle to rest against the top of it.

I guess the pan rails could be shaved to meet them, but...

Just wondering...

 

[Scott231]

Originally posted by QuickWrench
Scott, if unrepairable damage to a block occurs after having billet main caps and a girdle installed, can the caps then be transferred onto another block? Or is there too much material removed from the bottom of the caps when originally prepping them for the align-hone?

It depends on how bad the caps are. Severe detonation pushes down on the center of the main cap, the perfect half circle opening for the bearing becomes arched (or "horseshoe shaped" as Joe Reif put it). This may not be noticable to the naked eye, but the "acid test" is - How easily could you remove the cap from the block? You should have to fight to get them out cuz they're in the registers "so tight".

This could make the cap sit too far down into the block for the girdle to rest against the top of it. <snip> I guess the pan rails could be shaved to meet them, but...

No no. The girdle sits above the pan rail by .005" in order to preload the main caps. If the meaurements are off, the girdle kit comes with shims.