TM400 Balancing

[firko]

Because I'm a newbie with open class Suzukis and in preparation for the Jens Olsen rebuild of my TM400 engine, I've been doing a bit or research on the model by talking to a number of people who have vintage raced them over the years. The most surprising thing I've discovered is the number of piston failures and, in two cases snapped con rods. I actually examined the broken rod and the remains of Suzuki211s TM400 piston and it ain't pretty folks! A friend of mine in the USA had a similar experience a couple of years ago that he supposedly solved by rebuilding with a full circle TS400M crank. Both Suzuki211 and Wayne my US friend are both long term Suzuki racers who have an affinity for the brand so the failures wouldn't be put down to a poorly assembled engine, bad maintenance or an oiling problem. TM/TS400 owners also report excessive vibration, something I wouldn't have expected from a Japanese manufacturer. This brings to the fore the question... Could the half circle flywheels have an inbuilt balance problem that could be a part of the problem?

Jens is going to build my engine as a serious race unit which will include porting and ignition mods and a pipe to suit. My question to any Suzuki tuning experts out there (Lozza?) is....Should I be looking at recalibrating the balance factor of the engine in an attempt to overcome any supposed vibration problem or whatever is causing piston and rod failure?
Frank Stanborough altered the balance factor of my Maico ever so slightly a few years ago and the previously 'shaky' engine bacame as smooth as an electric motor. I watched him going through the process with Alan Jones new Monark/Lito engine last week and recalling Suzuki211s experience, figured that it wouldn't hurt to recalibrate the balance factor of the Suzuki Crank,rod, piston and ignition flywheel as a unit before I take the lot down to Jens.

I'm reporting these problems as they've been reported to me and now that I am the owner of a TM400, I'm deadly serious about turning it into good, (reliable) race engine, that's why I'm going to the old Norwegian. He knows these things inside out.
So, in closing, am I on the wrong track with my balance factor theory and is it going to be worth the effort and expense?
Are there other 'problems' that also need addressing?

[Doc]

Firko I can't help with any usefull information on this but I've seen the results also and it seems anything over about 45HP from a TM400 is begging for it to spit a leg outa bed. I don't understand why either and put it down to the pork chop crank and the vibs it produces. This has to be where the full circle crank comes into play I'd reckon ya just need to find one is all. Fitting a TS400 flywheel and PE175 CDI unit may also help

[suzuki27]

Just a small point, and not exactly about crank failures, but every suzuki mxer I have owned over the years- about a dozen- the engine bolts are too small for the engine case holes. It is an easy fix,just drill out the cases etc to next closest size(Imperial) and get a correct bolt/hole arrangement. Some also needed shimming , as the gap between the engine cases and the frame was a tad too wide sometimes-and this from new. It will reduce vibration and was said to reduce frame cracks that were a problem on some of these bikes.

[LWC82PE]

yes and if you look in some suzuki parts books in the engine case or engine bolts page you can often see shims listed with AR (as required) in the quantity

[JC]

M,

Is there any consistency to where the pistons are breaking? 

If its the inlet skirt breaking off, is the inlet port too wide & deep w a too-flat floor so it effectively 'swallows' the back of the piston?

If its the rings breaking causing piston failure, are the engines (esp modified ones) running at around 8,000rpm or higher?

For  76mm stroke the dreaded 4,000 ft/min mean piston speed is exceded at almost exactly 8,000rpm, at which point ring flutter causes unreliability - potentially at least.

[Lozza]

Single cylinder engine balancing is probably the least understood concept in engine dynamics.The engine/clutch/gearbox will handle 70+Hp no problems, rod length/Stroke ratio isn't the best, but rev to 8-8.5k no problems either.You would need to dismantle the crank components weigh the reciprocating and rotating masses and calculate the balance factor from there, being a bob weight crank then you would have to ADD weight to the light side of the crank to alter the balance factor. Flywheel is never really a part of the calculation.First thing to address is the transfers,standard TS ignition/rotor is fine for mx.The only time I have ever notices vibration has been when the engine bolts were a bit loose, which has already been mentioned.

[firko]

I'm going to give the TM400 engine to Frank Stanborough to weigh it all up and to see where it stands before I pass it on to Jens. If he feels it will benefit from altering the balance factor, I'll get him to do it. Frank is a master of this rarely seen art, having headed the Honda Race Team Engineering dept during the 80s and early 90s and now developing some of the fastest and most tractable Matchless G50 and Manx Norton engines in OZ. Some may have seen his amazing Manx Norton Metisse in the Kevlar Kompound at CD5. Because I'm not using a Suzuki frame I may not have the vibration issues some have experienced. After seeing Daves broken rod and smashed piston I don't want that happening to mine.