Compression Limit

[boise_banshee]

What compression over stock can you run, before you need to start thinking about getting the crank welded?

 

I am 2600 feet up, so stock for me is 115. I have some 19cc domes and pro-design cool head, which would put me at 160.

 

I wanted to get some feedback, before I install. I have to order a o-ring kit anyway, so if needed I can also pick up some larger domes.

 

Thanks!

[bansheesandrider]

What compression over stock can you run, before you need to start thinking about getting the crank welded?

 

I am 2600 feet up, so stock for me is 115. I have some 19cc domes and pro-design cool head, which would put me at 160.

 

I wanted to get some feedback, before I install. I have to order a o-ring kit anyway, so if needed I can also pick up some larger domes.

 

Thanks!

My crank let go with a stock motor that had a set of pipes on it and nothing else.I bought the bike brand new 16 months later I had a $750 repair bill, doing all the work myself. I was warned to get my crank welded, but I thought I would be OK with a stock motor. All the Banshees that I have bought since that one have been torn down and had the crank welded ASAP.

[boise_banshee]

that sucks

[BigRed350x]

To be honest, there's no set limit that it will happen. It goes to the life of the crank... how well it was taken care of, how hard its been ridden in the past, if the two cylinders were running equally throughout the cranks life, etc. There's a lot that goes into it. Generally I would say that once you go above the 155 mark, which is where normal pump gas will start to detonate, I would suggest getting it trued and welded before going higher. Timing advance also comes into the mix. The more advance you have combined with compression could lead to a shorter crank life. But just like the guy above said, even a stock crank on a stock setup can come apart.

 

I get them trued and welded anytime I go higher than 155psi static compression and +4 timing. With your 160 if you're running timing advance with it too, I would suggest getting it trued and welded. That's JMO though. Everyone will give you different opinions on this one.

 

I run 185lbs compression and a dyna with a custom curve that hits 14 degrees of timing on my big block twister, and 90lbs compression with a stock head and 4 deg timing on my little stock stroke and its got a trued and welded crank. Its just a good idea to get it done whichever way you go, if you can afford it, and can afford the down-time of tearing the engine down and getting the crank welded up.

[banshee67]

our 87 has the crank it came with when it rolled of the factory. same with our 94. so idk. in our 87 we tookk it out too glamis where it had a melt down due to deto. compression was around 180 psi. didnt know we were running too low of octane until it went kaboom.

[boise_banshee]

Well, guess I am split'n some cases this winter.

 

I might just have to send my cylinders to get ported at the same time..

 

 

Is the spot weld on a stock crank enough (hope so) or is a hotrod crank worth the investment ?

[dirtydownunder]

not even age has a factor, mine was 40 odd hours old and was quite a bit out when i had it trued and welded. and that was only 141psi and +3 ign adv.

 

if you can, get it done.

[boise_banshee]

yup, I feel sick thinking about the possibility of my crank crap'n out on me in bfe.

[boise_banshee]

Are the hot rod cranks worth it over the weld/true job?

[dirtydownunder]

you even weld or re-weld (on the stroker cranks) the hot rods.

 

the stock cranks are pretty good, just get yours trued,welded and checked out, to save you some coin.

[06specialedition]

I had mine trued and welded first thing. It's worth the piece of mind IMO... I've heard them coming apart on just a piped and filtered bike

[AKheathen]

yah, you will get 100 different answers, and really , there is a lot more out there that push the stock crank beyond what everyone testifies to, but it's all luck of the draw. i say, if you need "race gas' then you need it trued and welded, but really, any stock crank needs welded.........

[Burt Reynolds]

I wouldnt tear it down and weld but thats just me. Our 06 has been running around 160 psi for three years,we run 2 gallons of turbo blue with 3 gallons of 93 octane,mixed in a 5 gallon can of course. WE have been running the hell out of it for 3 years now on the stock crank---maybe were just lucky

[rubberneck]

ive had 3 stock motors (pipes reeds etc, but stock heads) separate cranks on me. All the bikes were used when i go them, but i will never own a banshee without first splitting the cases and welding the crank. Its just not worth a ruined trip for a relatively inexpensive and easy job. I say weld it no matter what you are going to do, then forget it. Its a perfect time to go in and upgrade all the little things while you have the side cover off anyway. Weld the crank, put in a modded shift star, check out the idler gear bushing, billet basket and billet water pump. then put it all back together and forget about it.

[sleeper06]

I personaaly like 145 psi for stock crank