jaylael Posted March 2, 2008 Author Report Share Posted March 2, 2008 Hodakas were invented here! It's almost as if it were an American made dirt bike because the guys who sorted out the designs are all friends of mine nowadays, though these guys were also my childhood heroes as well. As if that isn't enough reason, the Hodakas are cool and fun and well loved almost by everyone who comes in contact with them. I was riding a 1964 Hodaka 90/100 trials special built by Whitey "Hacksaw" Hartman beginning in 1972 at age 13. Should have kept riding the thing but switched to a great big cow of an OSSA in 1974. Took several years to get good at riding the bugger, but then I moved on to making my fame and fortubne as a "pro" motocross rider. If I knew then what I know now, I would have stuck with the Hodaka. Somehow I hadn't the vision of the perfect Hodaka trials bike as a 16 year old kid, and really wanted to try and emulate Mick Andrews and Joe Guglielmelli. In hindsight I realize just how fantastic they (Hodakas) really are and potentially could be. Quote Link to comment Share on other sites More sharing options...
jse Posted March 2, 2008 Report Share Posted March 2, 2008 "I have tested several different cyl. heads, and cylinders over time and definitely feel as if I am getting the best combinations narrowed down. I have been very pleased with the iron model 94 wombat cyl and the amal mk 2 carb with the old Gem reed valve, and an O3 cylinder head with no head gasket and anaerobic sealer used in place of a head gasket, applied sparingly. The silver paint thing did not work well for me, developing a combustion leak over time. (Yes the surfaces were flat lapped and torqued to 18 ft lbs.) With this combination the orange and green "Tree-Frog" runs really good and the compromise is just about right. It has schnurle loop scavenging accomplished by ports hand cut by me in the cyl running up from the intake passages to the transfer port height so they all pop open at the same time. " The Trials combustion chamber has a much wider squish band and sometimes re-machining works wonders, keeping the squish measurement to about 1mm (you could probably get away with .8mm due to the smaller bore/piston and lower RPMs). I built up and re-machined the head on my 85' TY350 to a true hemi style rather than the cone shape that is stock. It totally eliminated the famous "TY knock" and really improved the bottom end delievery. I replaced the stock 8-petal, open cage, steel reed setup with a reedcage and manifold from an 87' CR125, which is a 6-petal and has a "stuffer" in the cage (a formed insert to keep the intake charge intact) and Boyesen KX reeds. It's not such a big change to ride the TY now after being on my Pro (I fall off my TY and the Pro equally well....). The Schnurle Loop Principle is very effecient and you might want to try "progressive" port/time area changes, i.e., opening the rear boost port a few degrees before the rear transfers and the rear transfers a few degrees before the forward ports. This starts the intake loop-direction early in the cycle and helps low-RPM scavenging. I used this in the SX engines with good success and since you've got the reedvalve to work with, it's an option. Jon Quote Link to comment Share on other sites More sharing options...
jse Posted March 2, 2008 Report Share Posted March 2, 2008 Hodakas were invented here! It's almost as if it were an American made dirt bike because the guys who sorted out the designs are all friends of mine nowadays, though these guys were also my childhood heroes as well. As if that isn't enough reason, the Hodakas are cool and fun and well loved almost by everyone who comes in contact with them. The little Ace 90's were just about the most adaptive bikes I've ever seen. I saw them in just about every configuration: Trials, MX, Cross Country/Desert, RoadRace and even a little hillclimber or two. The Volkswagon of motorcycles! Pabatco was an amazing company. Jon Quote Link to comment Share on other sites More sharing options...
jaylael Posted March 2, 2008 Author Report Share Posted March 2, 2008 Now that's the kind of information you can't get just anywhere. Sweet! I will look forward to trying it. The newest bike will be a good testbed for these kinds of tuning options. I took a quick shot of my other current project. This is a reasonable facsimile of the kind of Hodakas people used to ride when I was a kid. This is based on an Ace 100 B frame, forks, with a Wombat swingarm, an early type reare hub which is 3 lbs lighter than the six bolt hub. The pending exhaust will use the chrome tool can for a glass pack. I will be using 1 1/2" header pipe. Quote Link to comment Share on other sites More sharing options...
jse Posted March 2, 2008 Report Share Posted March 2, 2008 Now that's the kind of information you can't get just anywhere. Sweet! I will look forward to trying it. The newest bike will be a good testbed for these kinds of tuning options. I'm not sure what the port/time area spec.'s are on the Hodaka cylinder. My TY had the usual Japanese engine problem with bikes in the 80's with too much transfer port/time area, so cutting the base of the cylinder to lower all the ports reduced all the time/area (and tightened up the terrible squish clearance, almost 2.5mm in my engine) and allowed me to re-shape and contour the transfer's for progression and re-shape and widen the exhaust. Changing the exhaust that way allowed for much better scavenging without resorting to raising the port height beyond the stock spec. Jon Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 2, 2008 Report Share Posted March 2, 2008 I built up and re-machined the head on my 85' TY350 to a true hemi style rather than the cone shape that is stock. It totally eliminated the famous "TY knock" and really improved the bottom end delievery. I can't recall if my KT250 had a squish band that didn't squish or if it was just an open chamber, but I welded it up and remachined it to have a real squish band. After that I retarded the timing from stock. I made a survey of all the trials port specs I could find and made some minor modifications to bring anything on the KT that seemed too far away from the common number back into that range. The new pipe with long header finished off the engine mods. It seems to run a bit better and doesn't have detonation problems. You sure can't trust that the factory (whichever factory it might be) came anywhere close to where they were aiming on a production bike. The works bikes will have the extra attention done to fix that stuff, but the retail customer pays their money and takes their chances. cheers, Michael Quote Link to comment Share on other sites More sharing options...
zippy Posted March 2, 2008 Report Share Posted March 2, 2008 Hey Jay, Yep that's a good enough reason if I ever heard one. Quote Link to comment Share on other sites More sharing options...
jaylael Posted March 4, 2008 Author Report Share Posted March 4, 2008 (edited) You guys have given me alot to digest. First off, Hello Michael. Great to have you on board TC. I'm sure you recognize your photo of the red bike w. alloy tank, which I pinched. I call it type 1. It was built in Y2k, and was shown at the Goldendale W/R. No longer own it or Type 2. Life goes on. JSE, wouldn't happen to be Jon Stoodley Enterprises? The Gas Gas Guru? I could be barking up the wrong tree on that one. I am great at embarrassing myself on the internet. Zippy I need to get better ecucated about these squish bands. I think I need to get more into fiddling with that. What I DO know something about in this regard is the compression tests I have done with a gage for comparison sake. Also I have had an expert machinist join forces with me who I regard as a genius, Mr. Ron Liddle. He was a so/cal tuner and learned a few secrets from some of the best tuners in that area in the mid to late 1970's. He knows his stuff and has built some incredible machines including the super hot rod Combat Wombat which I hope to unveil this spring. Anyway, Ron has made me one very special high comp head to play with which features the hemi combustion chamber. I guess I need to measure the squish with dabs of modeling clay then measure their thickness after bolting on the head is this correct? The relative tests with the compression gage rated this head higher than the stock Combat Wombat head by about 30 psi. That's some serious comp. No clue what the squish band is on this or any other. Too busy running around building all this cool stuff. In time I will get there. I put the ultra high comp head on the race bike. Figure it would be too high for trials. That thing is even a little hard to kick for a 125. Might try that head on the Sherdaka before I'm done. These Hodakas seem to run smoother at low revs with the lower comp head. I have even tried a 1/8" spacer with the model 94 head and I still have it in a box. I decided that was going in the wrong direction because it caused the bike to become less responsive and generally anemic. Anyway these are my thoughts at the moment. Gotta' go. Jay Edited March 4, 2008 by JayLael Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 4, 2008 Report Share Posted March 4, 2008 Jay, if you hadn't built the bike I wouldn't have been able to take a photo of it, so fair is fair. Setting squish clearances can make so much difference in things, especially in re detonation. People who want to add extra gaskets that widen squish (presuming they actually have some) in an attempt to lower the compression are just going at it the wrong way and may end up with an engine that is even more prone to detonation. A friend of mine has been known to not only weld in the chambers on TL Hondas to get some squish, but then build up the gasket face with weld too. This lets him have a larger volume combustion chamber (due to the extra depth) for the lower compression and the squish area too. He does then have to lengthen the cam chain, but he figures it is worth it. After I welded up the KT head and machined in the right level for the squish band I tried to recover some volume by grinding around in the top of the combustion chamber. Your best bet is to do what I forgot to do, which is measure the chamber volume before you start. Then you have something to shoot for. A low compression head with added squish bands for a two stroke probably needs to be a thicker casting than stock, unless you are lucky enough to have a head that uses a long reach plug and has enough meat around the stock combustion chamber to allow you to machine the head thinner from the inside of the chamber. Those little combustion chambers that you can see under the water jackets on some roadrace engines must be really handy as they can be made fairly readily on a lathe and mill without having to worry about starting with a much bigger piece of aluminum and then putting fins in too. If you were to do a new casting for Hodaka heads I'd suggest you design it thick enough to work as a trials head (large volume chamber) and then just machine away on the gasket face to reduce the volume for a high compression race head. I know people who are serious RR tuning types (TZ stuff) and they get into calculating the speed of the gas being forced out the squish area and figuring out what angles the squish band should be at, how wide it should be, etc etc etc. I think for a trials engine if you can get some functioning squish without driving the compression up you're probably making enough of an improvement so that the arcane technical details shouldn't be much of a worry. And the RR types are looking at 10-12K RPM operating speeds which is a bit different environment from a trials bike. Once you get the squish working and helping the turbulence in the combustion chamber (this may be something else the RR types are worrying about if they don't want to interrupt some carefully figured out scheme of loop scavenging) you can often back off the ignition timing too. cheers, Michael Quote Link to comment Share on other sites More sharing options...
bullfrog Posted March 4, 2008 Report Share Posted March 4, 2008 Hot dang I had fun reading all 5 pages of this thread! While the "engineer" side of me worries a bit about the combination of the "bent down-tubes" (which aren't tubes), the length of those front frame members and the hardware store variety of the aluminum bar (usually dead soft) - the "experimenter" in me is tickled pink watching this project from the side lines (and I agree that bracing to the front of the engine is a good idea . . . and further, I sure don't have any clear recommendations on how to handle it any better for low bucks on the first design iteration.) It is coming together!!!! If it turns out that the added front frame members need a tweak later . . . so be it . . . just let me know when the queue starts to form for test rides! Ed Keep the rubber side down! Quote Link to comment Share on other sites More sharing options...
bullfrog Posted March 4, 2008 Report Share Posted March 4, 2008 oh yeah, sometime why don't you take a full (direct) side view photo of the machine so we can see a sort of "engineers" view? Ed (what I said earlier about the rubber side . . . and down) Quote Link to comment Share on other sites More sharing options...
bullfrog Posted March 4, 2008 Report Share Posted March 4, 2008 Jay . . . and just one more, "Oh yeah" comment. Didn't I see a pair of genuine Hodaka head braces bolted up? Which will be big time brace/stressed engine frame re-inforcements! So the front frame members will just be helping out a bit - could be A-OK. Dibbies on first position in the test ride queue! (Well, after you of course!) Ed Quote Link to comment Share on other sites More sharing options...
Guest majestyman340 Posted March 4, 2008 Report Share Posted March 4, 2008 Some purists might be outraged by such a project. Normally I too find engine swaps to be a distasteful subject, but... after several years trying to keep from doing this, I just came home from work one day and started in on it. I guess the winter weather has effected my judgement.The front subframe has been welded together out of alloy strap material from the hardware store, and short chunks of renthall handlebar. It's very satisfying to be able to make something like that, finally having a tig welder to play with. The project has a long way to go, but should prove to be a fun ride and a great conversation starter. Also perhaps a handy excuse for lackluster finishes in modern events. Just a thought...............wonder if you have enough clearance between chassis/exhaust and front mudguard, when forks fully compressed? Quote Link to comment Share on other sites More sharing options...
jse Posted March 4, 2008 Report Share Posted March 4, 2008 "JSE, wouldn't happen to be Jon Stoodley Enterprises? The Gas Gas Guru? I could be barking up the wrong tree on that one. I am great at embarrassing myself on the internet." Guilty as charged. Don't feel too bad about embarrassing yourself on the Internet, Jay, I think I've cornered THAT market..... On the squish measurement proceedure, I've found (unless you are looking for a full chamber casting mold) two pieces of soft solder formed into curves, inserted through the sparkplug hole-one to front and one to back to compensate for piston "rock"- and then the flywheel rotated with a wrench (don't use the kickstart) will give a much more accurate measurenent. The clay mold is a LOT more work and the plasticity can lead to false measurements. If you were getting into razor thin clearances to get the absolute last ounce of performance (like building engines for the horsepower-crazy kart guys) you would probably use just one piece of solder at the front to simulate the piston angle under load, the front of the piston being the "thrust surface", but for Trials, two pieces, front to back, are a better "real world" way to do it. Michael is a gearhead like me and knows that you can get real nutty when it comes to combustion chamber design. When building roadrace engines, I'll be concerned with things like calculating "MSV" (Maximum Squish Velocity) and juggling the clearance, piston/head angles, blending radius, blah, blah, blah to get performance gains, but a Trials engine to be used by regular riders is a much more forgiving powerplant. Jon Quote Link to comment Share on other sites More sharing options...
michaelmoore Posted March 4, 2008 Report Share Posted March 4, 2008 Use some rosin core solder as it squishes with less pressure than the solid stuff does. cheers, Michael Quote Link to comment Share on other sites More sharing options...
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