3b pre-combustion cups (1 Viewer)

[Canadianmarty]

I’m in the process of replacing the pre-cups on my 84 bj60, and the new cups have a slightly smaller opening. Anyone have info on why this might be and what affect it will have? better starting would be nice as it gets cold here in the winter -30 Celsius.

 

[grayjs]

because they are new? they will be fine but make sure you get them staked in properly

 

[Canadianmarty]

because they are new? they will be fine but make sure you get them staked in properly

What do you mean by staked?

 

[grayjs]

Any machinist will know what it is - just an extra step that 'stakes' the precup to the head and prevents them from dropping in the future

 

[David*BJ70]

When I rebuilt my ex-3B many year ago, I had to « punched » the side of 2 out of the 4 precup in order to secure them in place.

 

[SuperDuperCruizer]

Wasn’t some vendor selling stainless pre-cups at some point?

 

[Canadianmarty]

Wasn’t some vendor selling stainless pre-cups at some point?

that’s what I bought, from aus though

 

[stevebradford]

Wasn’t some vendor selling stainless pre-cups at some point?

Dan at 4wheelauto in Alberta does. My factory Precups we’re not magnetic, possibly stainless from the factory?

4wheel Auto Parts

 

[SuperDuperCruizer]

Good to know for my spare 3B-T that needs a rebuild. Thanks

 

[gerg]

Factory pre cups were inconel. They were also crazy expensive. All aftermarket cups I've seen are stainless. Staking a pre cup won't stop it from dropping if it cracks in half. The broken cup would simply hammer it's way out. Loose pre cups can hammer like 1/8" into the head and block so I doubt they would respect stakng at all. Only reason to stake would be if it was loose and it made head install difficult.

 

[stevebradford]

I believe the head gasket compresses/holds them in place. Unless they weren’t installed fully into the hole and then planed flush..

 

[gerg]

When I do my head gaskets I usually put the head gasket on the block first. Super important to clean the precup recesses agressively so that they seit directly on metal. Any Carbon inbetween will feel as though they are seated securely but later I suspect the carbon breaks down allowing the cup to move which is a catastrophic process. I'm not a fan of machining flush as this gives the cup even less clamp pressure. I like them to protrude.