Crank Regrind

[driversdomainuk 8]

Hi

 

Sorry, a bit of a no brainer for most of you here, but during a bottom end rebuild I am aware that a crank regrind is often needed....why is this? and what part of the crank is regrinded..??

 

Cheers

[matty_gti 20]

Where the shells come into contact with the crank, after use or whereing of the shells the crank can become dented, pitted and sctratched after time which would then put damage on any new shells you may put in and cause shards of metal or filings to access your oil.

 

A visual inspection of the crank and a feel will tell you if you should have it done, or just take it to a place that does regrinds and ask if it needs it. Thats prob the best way.

[driversdomainuk 8]

thanks for that - but surely if you are going to regrind the crank the following can happen:

 

1) The crank will be "thiner" so is weaker - not great when I am warming the tyres on the start line

 

2) I would need slightly smaller shells as the crank will be thiner

[matty_gti 20]

Neither of these are a concern far as im aware.

 

All they do is take out the impurfections.

[Anthony 1,003]

Yes you'd need shells sized for a reground crank, but given that the maximum regrind on commonly available shells is only 0.3mm (from 50mm bigend or 60mm mains, so a fraction of a percent) then I think any difference in strength is minimal.

 

More of a concern is finding someone who can regrind a crank properly - but cross that bridge if your crank needs it, which they often don't if all the symptoms while it's running are good (ie good oil pressure, no knocking, no metal in the oil etc). Also, good 8v cranks are easy to find and it's argueably not worth the hassle of regrinding one - Mi16 cranks are much harder and more expensive to get though, so regrinding one is worthwhile.

[driversdomainuk 8]

thanks for that - another dim question I am afraid!! why would a crank which needs a regrind cause low oil pressure?

[geoffmslater 0]

If an engine has worn or pitted(etc) crank journals which needs a regrind, The engine would have generally have shown a lower than expected oil pressure. Excess clearance between journal and bearing which does not provide enough friction/back pressure to allow oil to be pressurised.

ie, When there is less resistance to the flow less pressure is able to be built up.

 

Anthony is correct, The peugeot cranks are quite strong and bigger than many designs to start with so a 0.3 regrind should not cause it to be a weak point of the engine.