29 replies to this topic

[fwdracer]

Rpm won't be the issue. It'll be the bearing loadings / structural integrity this will see in a boosted engine.

Have you ever seen the damage caused when a crank lets go? It is painful to look at and even more painful on the wallet!

[fastcarl]

I suppose it will depend on how much power  the engine makes  as to whether the crank lasts ,

 

 

carl

[propernasty]

i have the eaton blower on mine, bog standard SPI bottom end and crank, so far no problems, 3500 miles on the road, 2 hill climbs and a couple of track days. I never rev it over 6000, there is no point, the blower just keeps giving no matter what gear im in so just keep changing up. Blower is the best thing i ever did to the mini. 

[mini13]

I think you need to do some research,

 

cylinder presure will actually offset  the forces of piston G at the weakest point of the stroke ie TDC, rod bolts are the weak link.

 

its stagering the amount of piston G in an A series race engine, its comparable to an F1 engine.

 

 

Rpm won't be the issue. It'll be the bearing loadings / structural integrity this will see in a boosted engine.

Have you ever seen the damage caused when a crank lets go? It is painful to look at and even more painful on the wallet!

[fwdracer]

My research is carried out first hand. I understand about primary and secondary peak forces acting at TDC, but I've never had a rod bolt let go on a race A-series and have been racing with home built engines for 15 years. That statistic isn't down to luck. As stated - the amount of lightening carried out is just too much for the stock OEM forging. I've snapped an SH crank/wrecked an engine.

[MIGLIACARS]

Just my 2 pence worth.

again been racing 10 years used to have others build my engines, ive had a bolt let go before and it destroyed everything, but this wasnt at high revs just first lap out the pits.

warm up lap.

I really think the truth is somewhere in-between.

 

High revs do kill engines!

cranks that have had to much meat off them will let go big time.

 

in reality what you need is a good combination of it all and some one who can build them correctly. 

and with all high performance A series engine good luck.

 

We now build our own units and so far so good,

quick spec

167hp at the wheels

rotex blower

7 port head

dta 

arrow rods

 

 

crank has been modded a bit not hugely as i dont see the need to in my setup!

big boost at 17 psi.

 

 

i dont rev the knackers off it any more 7400 red line and so far so good, I hope ive found a happy medium here!

[Artful Dodger]

 

 

High revs do kill engines!

cranks that have had to much meat off them will let go big time.

 

in reality what you need is a good combination of it all and some one who can build them correctly. 

and with all high performance A series engine good luck.

 

 

 

 

 

 

this is basically it.  if you guys want some decent gear / advice then get on the phone to rob selby. im having a mini7 engine built by him and everything he has done and had made are just perfection.  his crankshafts (1000cc / 1275cc) are, in my opinion, the best out there at the moment apart from other units that arnt regulation specific.  disregard what people say about him charging the earth, i feel you get what you pay for!! 

 

PM me for more info if you like:)  

[Dusky]

Just out of intrest : any pics of an engine with a snapped crank?

[Midas Mk1]

From FB:

 

[fwdracer]

Horror story pictures? How's that for you? Nowt wrong with the rod bolts

Attached Files

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Edited by fwdracer, 11 April 2015 - 08:31 PM.

[minimole23]

looks expensive, any sign of where the crack started? They certainly like to fail at the centre main.

[carbon]

Horror story pictures? How's that for you? Nowt wrong with the rod bolts

 

So that's what happens to the SH crank... it did look a bit light for a well tuned 1275.

[Gr4h4m]

I bet that didn't sound nice..

[HUBBA.HUBBA]

Do they tend to stap near the centre stap?

[Inno]

Horror story pictures? How's that for you? Nowt wrong with the rod bolts

It looks like it was cracked at the central main bearing. I am in the process of lightening my crank and without any previous experience so apologies for ignorant observations.

It was not the most lighten place actually it looks relatively similar to standard cranck ...they took much more material from journals but it looks it didn't crack there.

Can it be something else beside lightened it? May be it was bent or may be they did something wrong with structure around central main or wrong hardening process?

 

Are those conrods lightened A series conrods?