TM 400 Full Circle Crank ? ?

[suzuki27]

Did anyone see the RN 370 replica on Mark's Vintage Swapmeet? It said a TM400 motor was used with a TS 400 Crank. I was wondering if this might be the source of the mythical full circle crank. It was listed on Feb 8th by J.P. Morgan.

[HuskyPete]

Rumor has it there are two of these full circle cranks on their way to OZ right now

[Lozza]

These will make fantastic paper weights if they actually exist
Here Kevin Cameron explains what the 74 750 Kawasaki triple had in the way of a crank.

What else could they do? Stuck with the small transfers, the next reasonable approach might be to raise the scavenge pressure by reducing crankcase volume. Again, they were up against a wall of physical law. In order to flow a crankcase full of mixture in the short timing allotted, the velocity through the small transfer windows had to become very large, so much that the mixture streams would curl up through the cylinder and out the exhaust well before the piston covered the opening. You might say, "Yes, but I thought the expansion chamber was supposed to send a wave that blocks the exhaust port, recovering some of the lost charge." The blocking wave has a duration and strength that are determined by, among other things, what size pipes will fit under the bike, and it can’t make up for such an extreme situation. The secret crank is not a full-circle design, and it surprises people to see that the racer is the same. Special full-circle cranks were in fact built for the higher scavenge velocity only reduced power, so they were put on the shelf.

Need anymore proof??

[firko]

They do exist. I have two on the way from the US. The full circle Suzuki crank came in the 1974/75 TS 400.
Lozza, once again you've quoted some text that merely displays that blokes opinion on Kawasaki triples. You can bet your sweet bippy there is somebody out there who's written an oposing view equally convincingly. But wait a minute, I thought we were talking about TM400 Suzuki singles here?
Me, I'll be going with the full circle crank purely based on my own hunch and that of the racers I've spoken to who've used them. I can't back my hunch that it'll work with a bunch of technical mumbo jumbo and new age science but can take the opinion of a couple of blokes who've done the conversion. If I can do something to improve an engine that has an international reputation as a piece of crap, I feel I've done something positive for mankind. If it doesn't work, at least I'll have proved to the disbelievers that the mythical full crank exists .

Now Lozza. I know this good cop/bad cop stuff is a bit of fun but does everything I do or say annoy you that much?   

[Lozza]

Not at all, I just found that when looking at an old Kevin Cameron article reaserching a build on a H2 750(basicaly 3 mx 250's stuck together engine wise anyway). If it were merely 'some blokes' opinion maybe but it's not it's Kevin Camerons' opinion(who worked closely with Gary Nixon and Erv Kanemoto back in the day). Kevin Cameron's technical writings and understanding(as well as machining and fabrication) skills are held in very high regard from his long standing column TDC in the old Cycle World magazine. That was not even Kevin's opinion it's what the Kawasaki engineers found at the Kawasaki factory race shop back in the 70's, and it's what the factory bikes used.The only thing a full circle crank making is more crankcase compression(and a bit less turbulance). If you have an alternate technical overview by all means find it and post it.I'll be happy to read it.
FULL CYCLE WORLD ARTICLE

 

[Doc]

Loz the full circle cranks do exist ( I was a doubter too) there was 1 on oz ebay just last week item# 130284490281

I put on a token bid of $35 and $37.00 is what the winner paid. Was in Dural? and only attracted the 2 bids, if I really planned to ride mine again I'd have chased it as to whether it makes any difference I've no idea but maybe in the case of a TM400 they do help. Beats me how it doesn't upset the secondary compression as 1 would think it would have a larger mass but it does kinda look physically small in diameter least one like me would think..never laid hands on one for comparison

[firko]

Being new to the Suzuki cause I don't profess to know much so I take note of those who have walked the walk before me. When I put an ad on Mark Holloways site asking if anybody could sell me one of the "mythical full circle 400 Suzuki cranks" I got many replies, some of them offering to sell me cranks, others offering advice. Not one of the replies gave me a negative on using the crank. Every single reply gave a positive reason for the move. Las Vegas builder/racer "Vegas Bob" Neilson who originally built the Tanner/Cozzy/Ray Sullivan Cheney TM400 and my Boyd and Stellings TM400 told me the full circle crank "turns the Suzuki into a Maico" while flat track racer Mike Middleton told me that legendary Suzuki dealer and racer Wayne Sumner used the full circle crank and outside flywheel ignition on his flat track teams bikes back in the seventies. Mike got Wayne to build him a Suzuki engine for his new vintage Boss framed Suzuki 400 p4roject and Wayne used a full TS400 full circle crank equipped engine as the core to start the development. Now Lozza, these blokes don't write books or dazzle us with volumetric efficiency arguments. They just build what they think works, just like the stainless steel filler rod discussion.

My theory is based on Suzukis own actions. By 1975 they'd got their act together pretty well, the RM was about to be released but the PE was still a couple of years away. Why then would the company go to all of the expense and tooling to change the crankshaft on a bike that had been basically untouched and unloved for nearly five years if it wasn't a positive improvement?

I've been told that the factory went into damage control in '72 when it was obvious that the factory supported TM400 riders on the USA domestic scene were getting hammered on their less than adequate TMs. The factory then built a batch of bikes for riders like Rich Thorwaldson and others with frames made by C&J and engines featuring full circle cranks among other tweaks. This transformed the bikes, making them far more competitive but still not quite good enough to knock over the then dominant Euro bikes. Obviously the engineers back in Japan took note of the improvements and it was rumoured that the '74 400L was supposed to receive the full circle crank but the bean counters didn't want any extra money spent on a bike that was about to be superceded so the batch of cranks that had been made were used on the TS400 which had three more years of production ahead of it. My source told me that a number of '75 TM400s also recieved the crank but it was never officially acknowledged. Sumner told me that he remembers doing a service on a customers '75 TM400 and being surprised to find the full circle crank. A couple of the C&J framed bikes have been discovered but it's believed that most of them were destroyed so the public wouldn't get to know of the deception.
Below: The Suzuki TS400 full circle crankshaft

[firko]

Welcome back Doc.

[lukeb1961]

This is fascinating stuff - Lozza, given that these things did indeed exist and apparently worked, what do you consider the reason(s) might have been for the improvement? (all arguments against being put aside for the moment!)

[Doc]

Thanks Firko I've heard nothing but good reports about the full cranks but my gripe is why the bloody  hell couldn't I find one in the 3x '76-'77 TS400 motors I ripped apart looking! This is what had me thinking they were mythical, I know there are people with them but I am still yet to see one of these cranks come from a TS400 engine from any year sold to the Australian market. My TS400 is stock standard original even down to the piston, it's a '76 A model and it definately has the pork chop crank fitted as per original from the factory so there's something weird going on whereby Suzuki seem to have fitted them to the later model TS indiscriminately I'm so confused!! thank God I've moved down a class to play with the 250's that had no such issues

[vmx42]

Hi Guys,
Personally I would like answers to two [well 3 actually] questions in this interesting tale:

1. what is the measured static mass of the full circle crank and the comparative mass of the original pork-chop crank [assuming that their external flywheel/ignition is common to both]?

2. what is the difference in the rotational mass and the balance factor of the 2 cranks?

3. and lastly what is the difference in the resultant crankcase volume when running either of these two cranks?

Lozza, I too love Kevin Camerons stuff. He really has a gift to explain technical concepts in a way that makes it easy to understand. He also loves to debunk common misconceptions [ie. the KR750 crank story]. To me it is one of the reasons that motorcycles in general are so facinating - what works on one bike, fails on another. You have to look at the 'whole', make [what you think are] logical conclusions and work from there - and then be prepared to go back to square one when your logical assumptions are proven to be less than optimal.

In the current March 09 issue of Cycle World he has a great story on this very subject. He looks at how modern race teams have specialists for every significant area of the bike- ie. suspension, electronics, tires, etc. The assumption being that all of these individual areas work in isolation and never overlap in practice - which of course is pure crap.
 
It does go some way to explain why teams run by strong willed, confident riders [ie. Rossi] and logical, methodical, experienced crew chiefs [ie. Jerry Burgess] make the other teams look 2nd rate on a regular basis.

The same methodology goes into making a great engine [I was trying to get back to the original topic, sorry]. Logic, methodical practice, experience and commonsense will often make a seemingly dog engine into something special.

Isn't good that we don't know everything, it keeps life interesting.
VMX42

P.S. and Doc good to have you back!!!

[Hoony]

.................................... I know there are people with them but I am still yet to see one of these cranks come from a TS400 engine from any year sold to the Australian market. My TS400 is stock standard original even down to the piston, it's a '76 A model and it definately has the pork chop crank fitted as per original from the factory so there's something weird going on whereby Suzuki seem to have fitted them to the later model TS indiscriminately I'm so confused!! ..............................

G'day Doc, good to see you back as well. missed your posts, i read them all.

i'm no Suzuki expert (or Honda for that matter) but here is a different take, perhaps the full circle cranks were only fitted to the USA market bikes and the aussie models had the pork chop jobbie? but then again was there any difference in different markets back then?

 

[Doc]

mmm..I was thinking the same thing Hoony, did we get delt second rate equipment here in oz? as far as I can tell, no. The ebay item last week was local and the seller and others have mentioned they pulled theirs from local TS400's. Just typical of my luck is all but isn't it ironic now that I'm not chasing one that ebay item appeared and appeared at really nice price VMX42 has the questions I'd like answered too but without side by side comparison I can do diddly..good to be back too people, call it a moment of temporary insanity

Suzuki27, I emailed JP Morgan enquiring about the crank in this bike when it first appeared finished and before he'd raced it. Same as everyone else, he said it mellows out the power and it came from a TS400 to which he gave the engine number..a '76 model of course

[VMX Andrew]

now this would have to be one the most interesting topics ive read in a long time...
probably cause i owned a 77 ts400 when i was just 12 years old in the mid 80s..
sorry guys keep it goin dont let me distract you all.....

 

[Maico31]

I'm interested to know about this full circle crank also. Does it have something to do with extra inertia from full circle crank wheels or extra weight that makes the TM400 engine behave better?