Cylinder cracking on 61x/62T

[Waternut]

The Riva girdled system is a tie down type to hold the cylinder. (base bolts or studs with threaded top nuts, then uses tie bolts from head to threaded top nuts)
Most of the time, the tie system does not use enough torque to hold the cylinder down, bolts are often 8mm and not 10mm in diameter. So I don't like tie down system, as it can help cylinder cracking but will not prevent it from cracking.

I agree that the pinch style head is the best when it comes to cylinder cracking problems. I'm an engineer so I naturally think of benefits vs consequences for every situation. The way I see it is this... If the 10mm pinch style stud breaks while riding (very unlikely) the broken stud could cause a big crank case air leak and this could cause a seizure where you lose the engine. If the 8mm tie down stud breaks while riding (unlikely but more likely than the 10mm breaking) you lose 1 of the 6 girdle studs, the crankcase is still solid, and the one broken stud won't make a lick of difference. You'll inevitably find the broken stud after the ride or after a few rides and replace it with no harm done.

That's just how I see the situation. Remember both cases are extremely unlikely but I'm a huge fan of redundancy in critical components. Both styles fix the problem they're designed for. They just both do it a little differently and they both have their weaknesses.

 

[Frosty]

i'd recommend a girdle kit... here's what happened to mine without a kit...

 

[nokfir]

i just put a bpipe on my ski. should i be worried about this same thing happening? or are we talkin about cracking from aftermarket non girldedheads or the stock ones as well?

 

[Waternut]

i just put a bpipe on my ski. should i be worried about this same thing happening? or are we talkin about cracking from aftermarket non girldedheads or the stock ones as well?

Actually a lot of this problem is caused by the b pipe. The b pipe puts more weight on the exhaust side of the engine which pulls up on the intake side. In addition, when the engine fires, it pushes the piston down but also pushes up on the head/cylinder. These two forces eventually fatigue the weaker intake side of the cylinder and it begins to crack until it finally unzips completely comes apart like Frosty's did in the pictures above. Obviously the higher the compression, the more force you put on the engine when it fires. It is definitely a fatigue problem and not a sharp blow that causes this. That means that the cracks happens over time. The harder you ride, the faster the crack will form.

So will you be fine with a stock head? The answer is yes...for now. I wouldn't want to ride the whole season without a girdled head though so put it on your list of 'must have' items. The casting process is not perfect and it leaves very small voids in the material on the cylinder. These voids are were the cracks start. The reason you hear of some people having problems and others not is the combination of riding style and casting void location. Finally, if you put a gouge in the cylinder when you're tightening the bolts, that doesn't help either.

Think of it like ripping a sheet of paper. If you pull on the edge of the paper, it resists a lot of tension. If you put a tiny little tear in that edge and pull again, the whole sheet rips apart with almost no effort.

 

[kevbo]

Dont get too wrapped up with the need for a girdled head. Ive been watching several ported 50+mph boats run for 5yrs, 100+ rides, without girdles. I will buy one when they get rid of removable domes and O-rings. Those two features guaranty ongoing maintenance problems where cylinder cracking has proven to be rare.

 

[onesojourner]

my ski had a bpipe on it for the 3 years and it was on there when I bought it. The cylinder had no signs of cracking. I had stock compression though.

 

[Polish jet pilot]

As in other motorsports - x-ray machine could prove handy to see hat's up with those jugs..

Frosty - holy crap! That is one big crack right there!

One more question on heads: what to use if all of them (aftermarket nowadays) use the oring system and removable domes?? How do manufacturers respond to blown orings problem or wrapped heads?

 

[Waternut]

Dont get too wrapped up with the need for a girdled head. Ive been watching several ported 50+mph boats run for 5yrs, 100+ rides, without girdles. I will buy one when they get rid of removable domes and O-rings. Those two features guaranty ongoing maintenance problems where cylinder cracking has proven to be rare.

my ski had a bpipe on it for the 3 years and it was on there when I bought it. The cylinder had no signs of cracking. I had stock compression though.

The casting process is not perfect and it leaves very small voids in the material on the cylinder. These voids are were the cracks start. The reason you hear of some people having problems and others not is the combination of riding style and casting void location.

This kind of goes back to what I was saying... It's takes more than one thing to fully crack the cylinder. Think of it like lining up the holes in swiss cheese. When the holes line up just right, it's toast. The big question is... How lucky do you feel?