PN 993713

[Hydraulic Jack]

No doubt this has been posted before, but here is the clearest discussion on detonation I have yet seen:

http://www.klemmvintage.com/deto.htm

[Hydraulic Jack]

And in case you missed the included link in the text above, or skipped it, here is a bit more technical discussion on what detonation is and how to avoid it:

http://www.klemmvintage.com/camerondeto.htm

After re-reading this white paper, especially the bullet points at the bottom of the article, and since the rider in our case is 200 pounds on a 100cc bike, it might be better in this case to gear down instead of gearing up, and let the bike wind up more. If it is lugging hard at full throttle, this might have caused detonation where it otherwise might not have happened.

[Joe Ormonde]

Here`s one that happened to me. In 1973 I reed valved and installed a close ratio trans in my 71 Rat. I ran it like a chain saw and never seized it. Then it was time for a fresh bore a few months later. Fresh bore, all new parts. Put it back together, broke it in and ran it through all 5 gears pinned and the engine locked up. What caused it? One of the ears on the kick roller retainer actually peeled and welded itself in between the kick shaft and the kick gear locking up the engine. Put the heavy duty kick roller retainer in your engine no matter what! Back then they didn`t have one. Joe Ormonde.

[DG29]

Joe,
What was the cause of you needing to replace the close ratio transmission that was already in your 71 rat?

[Joe Ormonde]

The model 93s came with a wide ratio trans. I installed the model 91 close ratio trans. The model 97 and 98 came with a close ratio trans. That was in 1974. Joe Ormonde.

[DG29]

I learn something new every day. I'd assumed my 93a came with a close ratio. I'd gotten it as a kid and was the second owner. The previous owner of mine must have installed a close ratio in it.

[Joe Ormonde]

DG29: I`m glad you brought up the transmission. The Model 92 and 93 series have the same transmission. First gear has a ratio of 3.5 to 1. The Model 91 transmission is 3.09 to 1. The Model 97 98 transmission is 2.9 to 1. The biggest + to the close ratio trans is shifting from third to forth to fifth the engine doesn`t bog down near as much. You just shift shift shift. First gear is a little higher than stock, about the same as the 97 98 transmission. This is something I`ve wanted to post: That Model 91 transmission second gear has 30 teeth, the same as the Model 92 93 does BUT the 4 balls roll and lock in the wrong place on the gear if you use it in a Model 92 93 transmission. Then you have NO SECOND gear! All of the gears mesh, but you can see they don`t line up. My nephew had a 1970 100B with no second gear. I tore it down and second gear had 91 stamped on it. You could see they just threw the engine together to sell the bike.A very rare shifting problem but I thought worth bringing up! Joe Ormonde.

[hodakamax]

Since I couldn't add anything about injection as it was after my Hodaka time, I guess I could mention that the 91 CR transmission was originally a replacement for the Ace 90's four speed. I ordered one of the first for my racing 90. The set came with instructions as it required some machining and different shifter parts. Someone posted the instruction sheet on the Forum a few years ago.

Getting on with the story, I do have this 91 CR gear set ready to install on the 2 the Max Project. I always hated putting that beautiful splined shaft inside the engine where it always hid unseen. How cool is this to a Hodaka nut like me?

There you are----

Maxie

[Joe Ormonde]

Yeah Baby: That`s it !!! HPI still has 91 gears too!!! I built a copy of the engine I had in my 93A back in the mid 70s . This trans is what`s in it! I like the 97 trans better simply because of the larger needles used for the kickshaft . I went to Ontario High School and in 1975 my buddy Danny Cobalt bought a MT250 Honda Elsinore. Guys out there just don`t know how fast you can get one of these older 100cc Hodakas to Run. I set up my 71 Rat for a 660 feet Drag Race. He found out! After I mowed him down 10+ times, he rode his Honda back to Ontario Honda to find out what was wrong with it. They rode it, said it was PERFECT! He informed them that a 100cc Hodaka shouldn`t be faster than a 250. Well, a lot of 327 Chevys mowed down 426 Hemis too! Joe Ormonde.

[hodakamax]

Heh Heh Heh. Yes, 100cc Hodakas were rapid at the time. My favorite story is when three of the Good's Cycle Shop bikes arrived at a quarter mile short track in Joplin Missouri in the Day. We were waiting in line for first practice when a new Yamaha 250 DT-1 engined TrackMaster framed flat tracker rolled up beside us. First class. Spools on both ends, monster carb and pipe with a cocky rider that ignored us peasants while waiting. A few warm-up laps with speed building and the two team mates and I all nodded. Two Hodakas on the outside and one on the inside all flew by him simultaneously. Worse yet he couldn't catch us or even keep up. Of course we were all giggling.

After the practice the guy approached us and asked "What are those things?" I answered for the group that the other two were hundreds but I was riding a 90. He just walked away shaking his head.

To say that this is true for for all 250's would be silly but we did make our point that night. Giggle, giggle.

Max and fast friends

PS--I still have my original Ace 90 racer and it was eventually stepped up to a 100 but not before necessary.

[Joe Ormonde]

What really bummed out the Hodaka guys like myself was that Hodaka didn`t tool up for a 250 race bike. We wouldn`t have cared if it was Purple and Pink as long as it was faster than the Honda. The Super Combat was and they only made it for 1 year. Why? It just seems that the people at Hodaka didn`t understand what was going on at the time or just didn`t care. All the money spent on the tooling for the Models 98 and 99 SHOULD have went into a 250 MXer. I would have bought one and Thousands of other guys would have too! Had Hodaka brought the Super Combat back in 1975 and had a 250 that scared the top pros, who knows how many investors they could have attracted! I`m still bummed out!!! Joe Ormonde

[Joe Ormonde]

Back to the Model 99! Lack of lubrication does get blamed far too often. Every Yamaha AT1,CT1, DT1 that had oil injection ran great: trouble free, UNTIL they disconnected the oil injection system. Go figure! Some guys mixed 20:1 and soon after a piston failure took place. Once again: Stock, Trouble Free: Altered, Trouble. Go figure!!! Joe Ormonde.

[matt glascock]

Wow!! This has been a really great and informative subject for discussion. I have shared the entire thread up to this point with Jay and the process moving forward, during the rebuilding of the motor, will be focused on detonation as the fatal flaw in the previous set-up. He feels that he has the machinery to emulate the torque groove concept as suggested by Hydraulic and will be using a timing light per the Captain's suggestion for point setting. Jay is an interesting guy. I have become the de facto liaison as he does not, nor will he ever, have a computer. I have been a beneficiary of this discussion and really appreciate all the time and expertise focused on solving this issue. Many thanks to all!!

PS- one of my last races on my '72 Super Rat before moving to RM250s featured my absolute demolition of a pair of fresh-from-the-crate 125 Elsinores. I still giggle about that.

[taber hodaka]

My race bikes were trouble free. The people at hodaka, did understand and they did care. When a big corporation buys out a small company, they do not care, they are only looking at the bottom line $$. I always ran for miles on overwind never had a problem, It was a 90 with everything in it, I ran 32:1 or leaner,--------------Clarence

[Bullfrog]

Matt, keep in mind that the exploded Toad experienced "creeping compression increase". The stock head was designed for proper (safe) compression with a standard bore. By the time the bore hit .060" over-size, that stock head provided compression which was a bit high. That alone MAY be the factor that destroyed this engine.
Ed

[matt glascock]

Yikes Captain! My Road Toad is on the same overbore. Do I need to worry about mine exploding too??? Last I checked I'm running just under 140 PSI. I don't run it that hard routinely, but on occasion I do take it for an highway run at WOT and also do a bit of trailing which can load it heavily on sand and hills. Other than that, its an around-town buzzer. Also, what is the theory behind the addition of "torque grooves". Adding volume to the squish area? Adding volume to the cylinder in general? Creating turbulence to effect the flame front? What's the skinny? Thanks Captain!

[Bullfrog]

You listed 160psi for the Toad that croaked . . . and 140psi for yours. That is a very important 20psi difference. I'll let racerclam expound on the virtues of torque grooves (since I don't know much about 'em at all).
Ed

[Hydraulic Jack]

The grooves create turbulence, and a side effect of cutting grooves is that combustion chamber volume is slightly increased, which slightly reduces compression. The change in compression is not really the intention. Turbulence is. If you read through the linked Klemm articles, turbulence in the squish is mentioned as an aid in reducing detonation. An added benefit, and the reason I believe they are called torque grooves, is that the turbulence increases burn efficiency, giving just a bit more power with no other changes. If you read around on the internet you will find guys that say the grooves are bunk. Don’t believe it. These guys might not understand the theory, and have never tried them. I do, and I have, and they work.

There was a fellow that used to post here from time to time who has a shop in (I think) northern Utah or southern Idaho who does a milling machine fluted surface on cylinder heads. His principal market is snow machines but the intended result is about the same. The fluted surface creates turbulence, and does what the grooves do. Whether one is any better than the other hasn’t been established with science as far as I know. Both methods can be expected to offer improved resistance to detonation. One is simpler and less expensive than the other.

[matt glascock]

Toad...Croaked... Good one, Captain. Yep, 140ish PSI. I had to check it after I got it bored because I could start the motor using my hand on the kick crank making me think about a serious lack of compression, but 140 PSI it is. Must be something to do with the architecture of the kick crank. Thank you, Captain. Hydraulic, after reading your post, I went back and perused the article you linked to regarding detonation and it all makes sense now. Thank you. You are absolutely correct. That really is an excellently presented and concise treatise on the subject of detonation. Now, I'm quite paranoid thinking of my bikes with pumped up motors.