Crankshaft sizes and 500+ bhp

[mark shead]

650hp is fine on .25 any more and you should be using a aftermarket crank anyway.

Mark

[xpower]

Mountune used to say any competition engine over a genuine 500 bhp needs a standard grind crank and that is when you could buy them new.
Most secondhand standard size cranks will need a grind due to wear on the centre main bearing (that includes all those members on here who sold me standard grind usable cranks, all of them needed grinding)
You will have the most bearing area and therefore a greater area of oil with a standard size crank as well as a crank which is physically stronger.
Any crank which has run a bearing I would scrap as they bend like a banana and unless they straighten in a press all you can do is grind them straight.
Often when you see a difference in finished grind sizes, that will be the case and when they are ground like that they will need balancing.

Steve

Hi Steve

Mountune would never ever use a ground crank in any yb engine full stop , even if it was a 300bhp rally engine

If a crank is bent I wouldn't even bother straightening , it goes straight in the bin !

The std crank in a yb is good for over 700bhp if revs are kept sensible and the weight rods and pistons kept to a min. It will be very hard now to find a new crankshaft , So only option now is to go with a arrow crankshaft

I am trying to think when I last saw a std yb crankshaft break! ( not due to bearing failures )

Bee interested if anyone's out there has photos of one, where it's failed by crack! And what revs torque and bhp it was running?

Regards Piero

[DAI COSSY]

Hi Steve

Mountune would never ever use a ground crank in any yb engine full stop , even if it was a 300bhp rally engine

If a crank is bent I wouldn't even bother straightening , it goes straight in the bin !

The std crank in a yb is good for over 700bhp if revs are kept sensible and the weight rods and pistons kept to a min. It will be very hard now to find a new crankshaft , So only option now is to go with a arrow crankshaft

I am trying to think when I last saw a std yb crankshaft break! ( not due to bearing failures )

Bee interested if anyone's out there has photos of one, where it's failed by crack! And what revs torque and bhp it was running?

Regards Piero

What's your view on a standard crank revving to 8-8.5 rpm running 500 is it a short life for the crank

[xpower]

What's your view on a standard crank revving to 8-8.5 rpm running 500 is it a short life for the crank

My view is build the engine to give 500 bhp@7250 rpm , why would you want it to rev to 8500rpm, to achieve 500bhp it will be more reliable less revs and not wear so quick Yes the crankshaft will go to 8500rpm, but you will need to make sure oil temps oil pressure and oil flow to bearings is addressed as well as other major components being up to the job
Regards piero

[steveboyslim]

Hi Steve

Mountune would never ever use a ground crank in any yb engine full stop , even if it was a 300bhp rally engine

If a crank is bent I wouldn't even bother straightening , it goes straight in the bin !

The std crank in a yb is good for over 700bhp if revs are kept sensible and the weight rods and pistons kept to a min. It will be very hard now to find a new crankshaft , So only option now is to go with a arrow crankshaft

I am trying to think when I last saw a std yb crankshaft break! ( not due to bearing failures )

Bee interested if anyone's out there has photos of one, where it's failed by crack! And what revs torque and bhp it was running?

Regards Piero

Piero,

I was referring to what was discussed with Dave over a curry after one the infamous driver who race an Escort Cosworth had enquired about the availability of new original YB crankshafts from Mountune probably after they were no longer available.
I do agree about bent crankshafts and in my opinion cranks which have run a bearing, I consider also to be scrap.
I have seen two examples of YB crank failure one many years ago at Oulton Park one of the Labbatts RS500, engine exploded, broke the crank even smashed the power steering rack, so much damage you could not tell what had happened first and the second was a 3 door rally car snapped just in front of the fifth main bearing.
The best bit in both cases the cranks were on standard sizes.
The problem is now non the available original cranks are new.

Steve

[steveboyslim]

Was my one ok Steve?


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Rob,

Yours is in mint standard condition, standard sizes ends and mains just needed a polish.

Steve

[c20tbo]

Rob,

Yours is in mint standard condition, standard sizes ends and mains just needed a polish.

Steve

Nice one Steve, did you receive email mate?


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[richyx]

Why not spend the money and have a farndon crank, I'm sure you can buy direct as well

[mark shead]

Why not spend the money and have a farndon crank, I'm sure you can buy direct as well

Until the nose falls of it. Buy a arrow or nothing imo.

Mark

[cossiedavid]

Why not spend the money and have a farndon crank, I'm sure you can buy direct as well

Waste of money buy arrow and forget

[lee2cossies]

What's the rough cost of arrows crank?

[DAI COSSY]

My view is build the engine to give 500 bhp@7250 rpm , why would you want it to rev to 8500rpm, to achieve 500bhp it will be more reliable less revs and not wear so quick Yes the crankshaft will go to 8500rpm, but you will need to make sure oil temps oil pressure and oil flow to bearings is addressed as well as other major components being up to the job
Regards piero

I understand what you mean,don't think my tuner would agree tho,which is why I ask as its good to hear other opinions my engine is built by Karl nms solid lifters etc forged pistons,standard crank,rods revs to 8 with t4 in all fairness it works well with the t4 I think you get the best out of that old turbo to be fair with the extra revs

[mark shead]

What's the rough cost of arrows crank?

From mem £1750+vat for the stroker version. I would not bother with a crank unless you are changing the rods which are the weaker link of the two.

Mark

[DAI COSSY]

From mem £1750+vat for the stroker version. I would not bother with a crank unless you are changing the rods which are the weaker link of the two.

Mark

Will arrow cranks rev higher as well mark

[mark shead]

Will arrow cranks rev higher as well mark

Matching everything correctly means it will be more reliable at higher revs the. You start to run in to oil pump problems along with higher bearing loads.
rods last engine did 8800rpm for 11k miles of hard use at 2.8bar boost on a Gtx4202 turbo.
But I don't see the point of revving a engine with a smaller turbo that high as the natural tendency of a yb is max power at 7250rpm unless you have the cam spec wrong.

Mark