Cause and Effect!!!

I'd be checking for crankshaft bent too and bearings damage insights and oil pump cast snout integrity and rods and bolts might be done for to trust again. I don't have enough time and money to get involved with real racing so sit on sidelines watching in awe those that can and do, just thinking how much they might get ahead on a tri-linked wonder.

Might as well add my two cents worth. At least I have plenty of experience with similar broken cases to base an opinion on.

I think concours has it right. The cases cracked from age fatigue and stress, not belt tension. I suspect the crack actually started at the rear of the case, and progressed to the main bearing area and on to the front of the case. Every broken case I've had has broken along the same line as yours. The first couple of cases I broke were both early 750 cases, and they cracked at the rear where the case is very thin. I caught them before the crack got very far, and managed to repair them and weld in some reinforcing ribs, and one of them actually survived additional racing. The other one eventually broke again, this time starting at the mainshaft seal area. I had two 859 crankcases, both of which had been reinforced with welded plates, break at the same event at Daytona one year, both on 920 cc engines. Running them at 7200 rpm on the Daytona banking turned out to have been a bad idea, but they were really fast while it lasted. I think stock cases will eventually break in a race bike that is making good horsepower and is ridden hard. My best guess is that the force required to reverse the piston travel at TDC keeps trying to pull the top of the crankcase up until it finally succeeds. If that's the case, using the lightest possible piston and rod small end weight should help, assuming you don't just rev the engine higher with the lighter combo.

I'd also agree with hobot about checking the crankshaft for cracks. The first case I ever broke also had a crankshaft with a crack almost 2/3 the way around the mainshaft at the cheek. I had the same sort of question as you about which came first, or if it was just a coincidence.

Ken

Peel intends to risk the extra rpm of JSM low inertia kit and monitor crank sling threshold to objectively creep up on red line or impeller cavitation or sonic port choke or friction flattening the torque rise. Ken has convinced me to follow the garden tractor pullers practice to strap head down on cases and cases to mounting hard points. Peel's will strap to cradle. Garden pullers say alloy cases are taboo as surviving winners only run cast iron blocks. Their side valves flat heads make similar power and rpm as our race engines. I don't think there's been a higher rpm test case than Ms Peel's over rev event whose 2nd breath of extra faster rev up ROAR started with tach needle already against the stop to bounce it invisible for some seconds after throttle finally slammed shut - which I think was only thing that really bent Peel crank by the extra suction drag of inhalling resistance. I rode Peel with huge winter wind screen for 2000 more miles but top speed dropped to 110 indicated and would not run out from under any more so tossed in the towel and started decade of bullet proofing power potential. Peel Combat cases had all stress risers at mount flanges ground out filled in and 2 plates at top bolts one on each case which allowed an 11th through bolt clamp force to help share loads on both case halves. It survived fine. Ken has made my dream come true so far. I don't know what elite racers have in their sights but Peel's most tempting targets are 4wd rally cars up Pikes Peaks now paved damit but also means I'll seek special permission to start a new Peak event by racing back down it. Motorcycles in tights on pavement are not in Peel's league to interest me anymore but fun to zip around for our solo orgasms. Tri-links G's power hook up delivery excites me more than the Drouin power by some margin and know 1200 hp rally cars and 250 hp cycles can out hp Peel in the opens but they may not have traction enough to catch up what they lose in the bends. Its the coming robotic cycles I am most concerned with if I live long enough.

Good analogies all round guys, thanks for your input, yes could well have missed a crack in the case leading up to the failure, and perhaps the backfire and loss of a bottom gearbox bolt didn't help, some of my friends had quietly mentioned, "wonder how long before his cases's split", like i said in a previous post, I had to start with something, so started with stock frame and running gear, and stock cases. Who knows what sort of life they lead between the UK & USA before landing in NZ!!!
Yes all will be done to check non damaged internals, it will run again and watch this space (hopefully under another topic heading) for a set of billet cases and crank to match!!!
Certainly not going to wait years for its revival!!!!
Found another fault a bit unrelated, but would have caused on going issues, exhaust valves to tappet geometry is not great, so as the valve rotates, the tappet is slowly eroding the edge of the valve.Inlets are fine
Regards Mike

Brooking 850 said:

Good analogies all round guys, thanks for your input, yes could well have missed a crack in the case leading up to the failure, and perhaps the backfire and loss of a bottom gearbox bolt didn't help, some of my friends had quietly mentioned, "wonder how long before his cases's split", like i said in a previous post, I had to start with something, so started with stock frame and running gear, and stock cases. Who knows what sort of life they lead between the UK & USA before landing in NZ!!!
Yes all will be done to check non damaged internals, it will run again and watch this space (hopefully under another topic heading) for a set of billet cases and crank to match!!!
Certainly not going to wait years for its revival!!!!
Found another fault a bit unrelated, but would have caused on going issues, exhaust valves to tappet geometry is not great, so as the valve rotates, the tappet is slowly eroding the edge of the valve.Inlets are fine
Regards Mike

Click to expand...

A good method to get the tappet sliding centrally on the valve tip (got this idea of a forum post) is to smear the valve tips with marking blue and turn the engine over. You can see where the tappet pushes across the valve tip, alter push rod length for each valve as req. I made up a set of pushrods with threaded adjusters so I could alter the length and then machine the rods going in the engine to the adjustable rod length - well worth doing on any pushrod engine.

hobot said:

I don't know what elite racers have in their sights but Peel's most tempting targets are 4wd rally cars up Pikes Peaks now paved damit but also means I'll seek special permission to start a new Peak event by racing back down it. Motorcycles in tights on pavement are not in Peel's league to interest me anymore but fun to zip around for our solo orgasms. Tri-links G's power hook up delivery excites me more than the Drouin power by some margin and know 1200 hp rally cars and 250 hp cycles can out hp Peel in the opens but they may not have traction enough to catch up what they lose in the bends. Its the coming robotic cycles I am most concerned with if I live long enough.

Click to expand...

I would think a Honda CRF 450 would be a good Pikes Peak race for you. They are in the 70 HP range (~ 2.5 hp/cu in), handle well and win with regularity. A year or 2 back they took all the fun out of the race by going to individual time trials rather than allowing the racers to run as a pack and compete neck and neck with their competition.

Ugh WZ no one but hobot understands how corner crippled everything else is to tri-linked Peel and seems to forget she once had the POW to literally run out from under me till 90 and i never ever found a way to upset her and live in conditions that make the unpaved PP event look like well groomed extra wide freeway. I get tripped out on my heated race tire SV650 every time I start to work up some turning G's, front or rear skips and shudders back through forks and frame, so my heart sinks back to ordinary corner crippled commuting rates. Just wish others could experience it to share the lasting highs. Its crazy making to me too to do it on such an antique with a few mods. I've been crazy in the bad ways too from fever, poisoning and trauma likely just aggravating karmic birth defects but Peel type crazy I seek no cure just more forever. Some few times if I didn't enter turns hot enough I'd get passed by a close follower soon as we started to get upright again. So I want to be able to run rpm up on less than WOT not to loose ground with Peel's ability to plant more power down than fat tired cycles leaned over some. In your engine breaks doing this what ya gonna do but lose it or spend some more.

Al-otment, there is a possibility the exhaust guides were put in incorrectly before my ownership, by the way the ports were 'attacked' before we got to , anybodies guess, so whats happened is the tappet lines up with the inboard edge of the valve even when fully depressed, almost as if the rocker arm is 3 mm to short!! Its not , just bad geometry

Hobot, this thread has got nothing to do with Peels handling , good or bad, as much as I get amusement from your comments.
I seem to have read your threads on handling in everyone elses thread , relative or not at the time,please dont rob mine.
Time to get Peel running my friend so we can all get some sense of reality from her travels, Emma Peel was one of my favourites to , dont let her memories wither away in your lounge room sitting on a milk crate.
Regards Mike