Crankcase crack.

jseng1 said:

SteveA said:

Al....

I was in Norman White's on Saturday collecting barrels, I chatted a bit with him about cracked cases. ....

....they were getting through two sets of cases a season until they significantly reduced reciprocating weight, and by more than Jims pistons and rods alone would achieve....but if I undersstood...at a cost beyond most that of us can bear...the outcome was no more cracked cases...

......

I have Maney cases and crank and Jims rods and pistons...so I am hopeful we can avoid cracks!

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Norman is using Titanium rods I believe and they are very expensive. I also offer an ultralight setup with underdome milling etc and a lighter rod thats good up to 80 hp (endurance racing). But I don't get many (or any) takers.

There doesn't have to be anything wrong with a street bike to crack cases and cranks. It just depends on how much your revv it. I think Comstock was lucky with his motor (until it blew - and what happened I don't know).

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If Norman White is using titanium con-rods then the reciprocating weight of the rod is going to increase in comparison to an aluminium alloy rod but obviously decreases in comparison to steel. Maybe he's had problems with rods breaking as well as cases.

acotrel said:

A light flywheel can be very disadvantageous. If you spin a heavy flywheel up then climb using more gears, it is often a better thing than spinning a lighter flywheel which doesn't have as much inertia (stored energy ). If you ride a commando engined bike with the heavy flywheel and it only drops a few hundred revs on every gear change, and stays near maximum torque - that is good. Initially it won't accelerate fast, unless you have a low first gear to get it going off the start, however once it is rolling and the motor is up in it's operating rev range and pulling a lot of gearing .... ?

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The advantage and dis-advantage of a lighter flywheel is a reduction of inertia. It's swings and roundabouts, the engine will rev quicker but as you say lose revs more quickly - but how quickly? A heavy flywheel will help a low powered, low revving long stroke engine to maintain momentum once it's got up to speed. Commando flywheels have their origins in the 1950's when many low powered bikes were being used for carting a sidecar and a small family around. Heavy flywheels are beneficial here to help maintain momentum. I don't think a lighter flywheel will be so critical on a higher powered engine when the majority of miles are rider only. Plus there's the benefit of faster acceleration.

Al-otment said:

jseng1 said:

SteveA said:

Al....

I was in Norman White's on Saturday collecting barrels, I chatted a bit with him about cracked cases. ....

....they were getting through two sets of cases a season until they significantly reduced reciprocating weight, and by more than Jims pistons and rods alone would achieve....but if I undersstood...at a cost beyond most that of us can bear...the outcome was no more cracked cases...

......

I have Maney cases and crank and Jims rods and pistons...so I am hopeful we can avoid cracks!

Click to expand...

Norman is using Titanium rods I believe and they are very expensive. I also offer an ultralight setup with underdome milling etc and a lighter rod thats good up to 80 hp (endurance racing). But I don't get many (or any) takers.

There doesn't have to be anything wrong with a street bike to crack cases and cranks. It just depends on how much your revv it. I think Comstock was lucky with his motor (until it blew - and what happened I don't know).

Click to expand...

If Norman White is using titanium con-rods then the reciprocating weight of the rod is going to increase in comparison to an aluminium alloy rod but obviously decreases in comparison to steel. Maybe he's had problems with rods breaking as well as cases.

Click to expand...

Well unless we weight his rods we won't actually know that comparison. Norman's point is that significantly reducing the reciprocating weight (Yes, I would also assume compared to heavy Carrilos rather than alloy rods, but I don't know that) he says he gained reliability and stopped needing to replace cases during a season. Since a motor will run to the end of a race with a cracked case, if the trade off to saving cracked cases was a rod through the side and an instant DNF, its hard to see that as either progress or VFM :?

meaning I don't think he was breaking any rods at all, before or after, and the titanium seems to have been for him, win win, with increased reliability and reduced squish clearance giving a bit more power. It just comes at a price most of us would find hard to justify.

Al-otment said:

After stripping down of primary drive and spraying penetrant dye and developer over the suspected area of the drive side crank case, the crack can be clearly seen and runs horizontally, 1/4" above and to the left of the top stator stud (Mk3), and runs left for 2.5". I was expecting to find a crack starting from the main bearing housing. This one has appeared in what I assume is a relatively low stress area and I reckon has been caused by a faulty casting.

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With this additional info it does sound as if you have had defective cases. It does also beg the question; are they repairable?

You have a solution that should keep you happy for thousands of miles, so.....if you want to sell them to me for a very modest sum I will see if I can get them repaired

I will not be mounting primary cases or alternator stators etc. or in fact anything around the top stud area of a MkIII

Al-otment said:

acotrel said:

A light flywheel can be very disadvantageous. If you spin a heavy flywheel up then climb using more gears, it is often a better thing than spinning a lighter flywheel which doesn't have as much inertia (stored energy ). If you ride a commando engined bike with the heavy flywheel and it only drops a few hundred revs on every gear change, and stays near maximum torque - that is good. Initially it won't accelerate fast, unless you have a low first gear to get it going off the start, however once it is rolling and the motor is up in it's operating rev range and pulling a lot of gearing .... ?

Click to expand...

The advantage and dis-advantage of a lighter flywheel is a reduction of inertia. It's swings and roundabouts, the engine will rev quicker but as you say lose revs more quickly - but how quickly? A heavy flywheel will help a low powered, low revving long stroke engine to maintain momentum once it's got up to speed. Commando flywheels have their origins in the 1950's when many low powered bikes were being used for carting a sidecar and a small family around. Heavy flywheels are beneficial here to help maintain momentum. I don't think a lighter flywheel will be so critical on a higher powered engine when the majority of miles are rider only. Plus there's the benefit of faster acceleration.

Click to expand...

I don't know the weight comparison details, but given that titanium is stronger than alloy, my guess is that the rods look similar to Carrillo's. if so they'll be lighter than both alloy rods and Carrillos.
whatever the weight situation, I do know that Normans primary objection to alloy rods is the amount they stretch and flex. By reducing the weight and preventing stretch, he was able to tighten up the squish, which as Steve A says, was less than .020" !! Try that with alloy rods and you'd not finish the warm up lap!!

When I was racing with stock parts - 1st my 750 cases cracked. Then I checked my 850 by putting the motor underwater and running compressed air into the breather. There were 7 hairline cracks around the PTO area. So I started developing the lightweight pistons and welded a reinforcing plate to the PTO side case. This was back the late 1980s



The 1st light weight 850cc pistons. One fin was milled off the cylinders to fit the shorter pistons.

Did you subcontract hobot to lighten up the parts?

Hee hee

Dud Dudes hobot is a late comer long after Jimmy first took over a drill in hand with gleam in his eyes... He still exceeds my scope of holey-ness plus he's drilled his already light modern JE pistons further yet. Ludwig left a comment on his featherweight wonder that there wasn't much he could take off engine mass, oh well.

Split the cases today and after applying penetrant dye and developer to the inside of the d/s case the crack can be seen to run from close to the top stator stud and makes it's way toward the cam shaft. No signs of any problems during the strip down, camshaft and crank turn smoothly etc. The developer has produced lots of small pink spots on the inside of the case in the area where I sprayed above the main bearing. I noticed this on the outside too but thought it was because I hadn't cleaned off the dye completely - I reckon this is indicating porosity within the casting although the only leak was from the crack - which I think is a result of flaws within the casting.

Sorry there's no pictures but if I'd bought a camera it would have been sold to help pay for the bits. At least the bike should be back on the road within the week. Another track day at Cadwell 17th May - plenty of time to get some miles in before then.

Al-otment said:

Split the cases today and after applying penetrant dye and developer to the inside of the d/s case the crack can be seen to run from close to the top stator stud and makes it's way toward the cam shaft. No signs of any problems during the strip down, camshaft and crank turn smoothly etc. The developer has produced lots of small pink spots on the inside of the case in the area where I sprayed above the main bearing. I noticed this on the outside too but thought it was because I hadn't cleaned off the dye completely - I reckon this is indicating porosity within the casting although the only leak was from the crack - which I think is a result of flaws within the casting.

Sorry there's no pictures but if I'd bought a camera it would have been sold to help pay for the bits. At least the bike should be back on the road within the week. Another track day at Cadwell 17th May - plenty of time to get some miles in before then.

Click to expand...

Don't you have a mobile phone? ;-)

I'm not going to bet you don't make it......

SteveA said:

Al-otment said:

Split the cases today and after applying penetrant dye and developer to the inside of the d/s case the crack can be seen to run from close to the top stator stud and makes it's way toward the cam shaft. No signs of any problems during the strip down, camshaft and crank turn smoothly etc. The developer has produced lots of small pink spots on the inside of the case in the area where I sprayed above the main bearing. I noticed this on the outside too but thought it was because I hadn't cleaned off the dye completely - I reckon this is indicating porosity within the casting although the only leak was from the crack - which I think is a result of flaws within the casting.

Sorry there's no pictures but if I'd bought a camera it would have been sold to help pay for the bits. At least the bike should be back on the road within the week. Another track day at Cadwell 17th May - plenty of time to get some miles in before then.

Click to expand...

Don't you have a mobile phone? ;-)

I'm not going to bet you don't make it......

Click to expand...

I do have a mobile phone but apart from being able to make and receive calls just about it's only other function is a torch...and some games, we're not talking state of the art here. My head can only deal with so much stuff at once. Spending time learning how to take digital photo's, down loading etc. is quite a way down on my list of priorities for the foreseeable future. I'll get around to it one day......

I have an iPhone......it makes a good torch too....with the right 'app'.....

It's well past time for me to upgrade and get a 20Mega Pixel Camera (far better than any camera I ever owned) that has a phone thrown in for free!

Actually I am not sure if I can call the phone bit free, the whole thing is thrown in with my contract......just waiting to upgrade because with this package I get 25M per day of data thrown in (free!) with European roaming!

Phone?....the thing I do least on it is make phone calls.....camera, text, email, weather reports, notepad, calendar, alarm clock, facebook, twitter, torch, gps/maps, soundmeter.....just need to get it set up for my easyJet boarding passes....

Catch up man!

SteveA said:

I have an iPhone......it makes a good torch too....with the right 'app'.....

It's well past time for me to upgrade and get a 20Mega Pixel Camera (far better than any camera I ever owned) that has a phone thrown in for free!

Actually I am not sure if I can call the phone bit free, the whole thing is thrown in with my contract......just waiting to upgrade because with this package I get 25M per day of data thrown in (free!) with European roaming!

Phone?....the thing I do least on it is make phone calls.....camera, text, email, weather reports, notepad, calendar, alarm clock, facebook, twitter, torch, gps/maps, soundmeter.....just need to get it set up for my easyJet boarding passes....

Catch up man!

Click to expand...

As far as keeping things simple go I'm way ahead!

Cell service is very poor in my area so didn't have cell phone first decade here after having radio phone before cell phones and each new cell phone while in major city. Mine is base line cheap kind but does have camera I've used twice and don't know how to send from phone to 'puter so just use digit camera instead. Some folks are camera shy anyway, like Ken Canaga who described his antics to hone bores and custom tapper bore for Peel, standing/bent over a wood base stand on floor using power drill going up and down timing his holding it more in one area than another then work up to smooth the transitions. Begged him to just turn on his GoPro on a bench to show us the athletics involved in his craft but nope. I'm half fast shopping for a smart phone but no interest in the cell service just the apps for engine monitoring and G force performance and weather and video streams and programing ignition curves. Likely a tablet will work best for this.