Cracked Barrel

mj43 · Post by **mj43** » Sat Jun 13, 2009 7:54 am

Normally they crack at the back.
These were my number 1 barrels.
The strengthening (not shown) wasn't as substantial as I asked for and the barrels cracked. Both barrels have broken at the back as usual and both through the strengthening - as I said it wasn't as substantial as I wanted. But this time the barrel cracked up front - crack goes through the water jacket into the transfer tunnel. Result is that it emptied nearly a whole rad and I run a big rad into the left cylinder during the PB 90's trackday. Motor was still running and it was only when inspecting the motor prior to Anglesey I noticed the crack. Took a tea cup of water out of the rad when splitting the motor !
As crank looked ok and on the basis the motor hadn't seized and I am out of new cranks I decided to leave the crank in. Result was the big end failed in the fourth race at Anglesey.
Lessons learnt.
1) Make sure instructions about strengthening barrels are precise
2) If in doubt change the part

ScottaKR · Post by **ScottaKR** » Sat Jun 13, 2009 11:11 am

Ouch....... That's gotta hurt.

Where was the strengthening added?
Were these standard height barrels, or were they shortened to run different pistons?

mj43 · Post by **mj43** » Sat Jun 13, 2009 7:17 pm

At the back as that is where they normally fail. I have noticed that the thickness of the front web varies between barrels these must have been just that bit weaker.

I am going over to plan B as with shortened barrels the barrels are just not strong enough. On the dyno you can see them lift.

Cranks will be rebuilt with longer rods and I will strengthen the barrels - still need to skim them as the welding distorts them slightly - about 0.1mm is usually enough.

Been planning to do it for a number of years - it is just all the time I had parts there never seemed to be a need to go down that route.