les3002

the bottom end on my cossie started knocking yesterday it ran for max of 1 minute and was switched off, hopefully the crank will have survived but looking through the history the crank has been reground once before it says mains 0.5mm and big ends 0.25mm how much can be the cranks be ground to, am hoping mine isnt scrap.

cheers les.

abdr500

iTrader: (1)

if your big ends are .25 then .5 should be fine even .75 for some people

les3002

what about the mains though, as i cant find any bearings larger than 0.5mm oversize, or do the mains usually survive?

thanks so far though

abdr500

iTrader: (1)

the only way to see if the mains need doing is to take crank out and see .it may just be the big ends

les3002

ill get the engine out and take the crank to a machine shop to be checked out, probably going to be best.

thanks mate.

Anonymous

As a general rule, when the big ends go, it pulls the crank out of true and you end up having to take metal off the mains to get it staight again.

Its not uncommon for this to be as much as .5 or .75 even when the big ends are only needing .25, so possibly you will find your mains need to go to 1mm or 1.25mm

1mm mains are available through people like PJ but you might have to wait a while as they probably wont have any in stock.


Only way to know how much of a grind the mains will need to straighten the crank is to do it, which is obvioulsy going to involve spending money just to find out, and then potenitally ending up with it not useable (i wouldnt ever go more than 1mm even if by some mircal you could find the shells for it)

les3002

hmm bit of tricky one then, with 1mm mains would it still be okay for around 350bhp?

maybe worth my time just finding a decent used one, how much do they go for second hand? i know burton sell new ones for like 1300.

Anonymous

Its not a case of "1mm = 384bhp is safe"

The further its ground the less time it will last irrelevant of the power level.


Depends on how bothered you are about having to pull it apart again, personally i find the engine so easy to pull out of and strip down from my car that i would be quite happy to use 1mm shells or even more, as when it goes i would just sort it out again, but if you are the sort of person who wants to just do it once and not look at it again for 50,000 miles or whatever, then i would say trying to find a good std/std crank was a better option.

The std bearings are cheaper too, by the time you have a grind and undersize shells you are looking at 200 quid+ probably if you go as far as 1mm.

So by the time you offset that against the cost of the standard secondhand crank its starting to look a better option than grinding a crank thats already been ground .5mm before.

Cost varies MASSIVELY i know someone on here who bought a std/std crank for 150 quid recently, but i doubt i will ever get that lucky and i know some traders charge 3 times that much and still manage to get it.

RWD_cossie_wil

iTrader: (9)

.75 bearings are fairly easy to get hold of, burton power list them I think, I can't say I have ever seen 1mm oversize, but I'm sure that Chip is talking with good authority . I have been told by a number of tuners/engine builders that a .75 crank won't last long at anything over stg 1, hence why I bought a complete bottom end for Ł800 with a 200 block and a std/std crank, as It worked out cheaper in the long run.

pee vee

I was concerned about this too, (before i just bought a new standard crank lol)

Cosworth themselves told me that they will supply bearings
to .5, which is where their tolerances finish,
and Still told me on a couple of occasions that .5 crank would
be ok at 500 bhp.

So i'd guess that going to .75 would probably be ok.
but to be honest the time and hassle of getting the 1mm bearings you are talking about you can just buy a crank thats already done.
I got offered a few on here before i got mine.

les3002

i think im just going to get another crank, as said i dont really want to do it again any time soon even though the sierra is nice and easy to work id be expecting it to go all the time and dont want that.

thanks for all the advice guys :0

les.