Case Reed 125 Hodaka Project

[thirdstone]

I enjoy reading other peoples project and get a lot of inspiration from them. Its nice to know i`m not the only slightly insane person out there.
I wanted to share my Case reed project . This is the second engine , the first was a ,"lets see what happens " type approach and now I know it works I wanted to make some improvements. I`ll be changing completely the top end and induction. The Stock size reed will feed the crankcase directly. Because of that there is no need for the stock intake ports in the cylinder so I will be resleeving the cylinder to clean that up and recover some piston support. One bonus is that I can redesign the exhaust port. I have tried making Auxiliary exhaust ports but the location of the cylinder stud holes makes it difficult so I`ve gone with a bridged exhaust port to get more time area without raising the port. In fact I`ve lowered the exhaust port and increased port area at the same time, I`m hoping I`ll get a bit more torque out of the engine by increasing the power stroke. I have used Software to come up with the port design , I`m keen to see how accurate that is in practice. I must admit I`m no guru with this stuff and you might cringe when you see my handywork , I`ve done a tonne of reading so hopefully things will work out.

[thirdstone]

The cases. The first set of cases had the reed block bolted on and during the cleaning up of the cases I lost some too much material so I had to run a center gasket. These new cases have sealed up and passed a leak check with out needing a gasket also having the block welded also reduces leak points and allows the return of a screw location that is lost in the machining process of the inlet passage.

[thirdstone]

The first design

[socalhodaka]

Wow, nice work.

[hodakamax]

Cool stuff!

[dcooke007]

Very nice..cant wait to see how this turns out.

Danny

[thirdstone]

I`m using a product called Port map anaylzer V3.0 thats available online. I could have used the , make every thing as big as you can method but I wanted to tread carefully and not waste cylinders. I guess the "make it big method" is great if you have a ton of experience however I don`t. So far my porting / tuning has gone well , I respect the original Hodaka Engineers with their port timing so the only thing I`ve done in the past is increasing port area by widening certain areas and trying to maintain good flow angles. The flow angle is something very important and often not given enough respect , very easy to screw that up. The program uses data from the Engineer Gordon Blair or Gordon Jennings. These two guys are published Engineers who many years ago applied maths to predict area and angles required to get an efficient gas flow through a two stroke engine.Its quite a science that I only understand a fraction of but it makes sense to me that the areas required are strongly related to time (rpm) . At a really basic level the EX ports job is to allow the cylinder pressure to reduce as low as possible before the transfers open so gas will flow into the cylinder so to get that right for the RPM you want is the key. This is the power (no pun intended) of the simulation.

[thirdstone]

This is a short clip of the prototype starting up within days of completion. At this point i didn`t know what would be the result. The case reed design allows the engine to rev freely , check out all the current 125 MX bikes...all case reed.
This design was fairly mild port wise and had the inlets blocked off with JB weld.
34mm Carb and Circle F pipe. Stock 97 head.
http://www.youtube.com/watch?v=Yg7ZQPA2ZgA

And this clip is the prototypes first outing at a test track. We ended up sheering all the clutch screw not long after this but I think that was from getting carried away with the jumps more than anything else. You can hear who it loves to take off in the upper rev range.
https://www.youtube.com/watch?v=ww0zcACvcV4

I wasn't able to get the links to work from within the message board however a copy paste to a web browser works if you are interested.

[gearyoliver]

Sure sounds good! 2 thumbs up!!

[matt glascock]

Holy craaaap dude!! That bike rips!!!! I'm not surprised you grenaded the clutch. Is the core bike a model 94 Wombat? I have a 94 Wombat I'm squeezing hard and detonated the stock 4-plate clutch pack. I'm now running a 5-plate pack from a Combat Wombat with improved plates and hardened screws - safety wired. You might want to look into that upgrade. The stock Wombat clutch pack is great for enduro work but (in my limited experience as above) not so much for a screamer. I won't open the wired vs. nylock nuts can of worms but am a firm believer in the clutch blueprinting instructions found on the club page. One quick question - what suspension upgrades are you running? I'd have to send out a dedicated fruits-and-veggies search party if I hit jumps like those on my Wombat with stock legs. Now that I have the motor dialed, I'm ready for suspension. What are you running? Thanks and great work!

[thirdstone]

Hi Matt you are right about the stock suspension.
This bike is still has pretty low cost suspension but works OK .The shocks are Progressive and the forks are 35mm 74 Honda XL350 jobs. Front wheel is a Hodaka Conical job. We have used an aluminium swing arm that has cracked a couple of times. The stock lengthened steel Hodaka arm gets some use and that is a tough as nails. That clutch was a blueprinted 4 plate job with stock screws and no cushioned hub. I now use a 5 plate with hardened screws and flat pressed steel lock nuts. I also have gone back to the cushioned hub. I may go back to the 4 plate. I think the weight of the 5 plate clutch is around 900 grams ? I did weight it once and was shocked at the weight.
The bike is a 94 frame and engine case but mainly 97 internals PVL CDI.

[thirdstone]

Matt
A few pictures from that test day.

[matt glascock]

This is really great work you're doing. Thanks for sharing. I will be interested to hear how durable the 4-plate clutch pack is with the cushioned hub. Thanks for the tip on the Honda front end. I have an XL-175 front end that I will take a look at. How much did you lengthen the stock 94 swing arm? Did you add any additional gussets or other buttressing to any of the frame components. What spring rate on the shocks? Sorry about all the silly questions. I have a pumped up M94 that I have recently decided to finish off as an open class MX bike. Unfortunately the vast majority of tracks in my district are SX. Tight turn, jump, jump, jump, tight turn, jump, jump. tight turn, rhythm, etc. etc. Less real estate and sells tickets, but would murder a stock 94 frame. Thank you!

[thirdstone]

Matt the lengthening of the swingarm is a common mod , I`ve never done it myself. I bought my Hodaka swigarm already done. 1.5 to 2 inch is what you need. I can vouch for the much improved handling with this done. Much more stable in the rough. The frame on the bike in the pictures at the test track is stock but the one for this new engine will be changed quite a bit , not for strength but to accommodate the new engine and airbox. These frames are very strong if in good condition, You could add some welds to the existing gussets if you are worried but I don`t think its necessary. One thing I would say to you is to work out a way to secure the footpegs. The bolts alone wont hold the mounting bar in place. I find the positioning wrong as well. For me they need to be full rearward , I bolted a spacer in the slot to stop them moving. On my new frame I have moved them even more rearward by grinding material and welded them in place , the pegs have been replaced with wider ones from a Honda CRF . They don`t fit straight up but with a bit of machine work can be made to fit. I have seen some guys weld on pegs like a 97 but be careful because the footbrake access needs consideration. The 97 uses a different mechanism. You cant fit a down pipe on a 94 with out some serious frame mods either.
I can`t remember the spring rates sorry.
If you can only ride a SX track then you need a modern bike . The tracks I race on are made for vintage bikes , small jumps and pretty smooth most of the time. That test track was a private track for all bikes.
I would highly recommend that you switch out the 94 rear sprocket carrier for a 97 one, it has an extra bearing. I destroyed my 94 carrier early on. While we are on that I would also try and find some new sprocket rubbers that Strictly Hodaka had made once. It will protect your gearbox from breakage.

[Bullfrog]

Woo woo! NEAT project! I'm curious about what exhaust port height you have selected.

On clutches - may I recommend the "Chapman Clutch Pack"? (Named for the originator of the concept, Phil Chapman - long time Hodaka racer and tuner.) It is an assembly order change which goes a long way to help control "racking" of the clutch - and I had a real forehead slap and "DOH!" moment when I heard about it! Simply install a toothed steel clutch plate between the steel outer cover of the clutch and the rest of the clutch pack. This assembly order REQUIRES some attention to make sure that last steel plate doesn't get pinched between the clutch cage and the steel outer cover. (The change eliminates friction forces trying to make the outer cover rotate/slip slightly on the clutch cage.) A great idea. Yes.
Ed

[matt glascock]

Agreed. I run a modern KTM 450SX-F which is perfect for our district tracks but am hoping to beef up the frame and suspension on this M94 to take the abuse and race it in open class. I like the technique for moving the pegs back and plan to do the same. I'm 6'3'' so having the peg back will help me get my inside foot up to the front hub. MY Hodaka race bikes all have 2" lengthened and reinforced swinging arms. Wheelies are cool but not fast. Thank you for sharing your project. Great stuff!!

[thirdstone]

Woo woo! NEAT project! I'm curious about what exhaust port height you have selected.

On clutches - may I recommend the "Chapman Clutch Pack"? (Named for the originator of the concept, Phil Chapman - long time Hodaka racer and tuner.) It is an assembly order change which goes a long way to help control "racking" of the clutch - and I had a real forehead slap and "DOH!" moment when I heard about it! Simply install a toothed steel clutch plate between the steel outer cover of the clutch and the rest of the clutch pack. This assembly order REQUIRES some attention to make sure that last steel plate doesn't get pinched between the clutch cage and the steel outer cover. (The change eliminates friction forces trying to make the outer cover rotate/slip slightly on the clutch cage.) A great idea. Yes.
Ed

To start with Exhaust height is 27mm , I can always go to 26 later. I`m curious to see if an extended power stroke has any noticeable benefit. Head Volume will be matched.


Hi Ed and thanks for the tip, i`ll check out next assembly time.

[thirdstone]

Trial fitting an air filter over a velocity stack. I thought I would create an airbox with a normal filter but I have this pod already. I might put this in a pod and work out how to support the rear of the filter.

[viclioce]

Looking really sweet! Can’t wait to see it finished! Victor

[Joe Ormonde]

I do see that one case had a Twisted Crank in it at one time. When I showed up at the Hodaka Shop back in the day, everyone there would look at my broken parts in disbelief! Things they had seen for the first time. The Splines shaved out of the Clutch Hub? A BENT Counter Shaft? A wrapped up and welded Kick Roller Retainer? You bet. If it`s a part iv`e broke it! I never did race on a track but when you constantly rev any Engine up to 10,000 RPMs all the time expect it to need a little patching up every now and then. I can predict that your main problem will be the big end rod bearing getting wiped out from the incoming air blowing off the oil. That`s what happened to the Kawasaki GREEN STREAKS! Constant Crank Shaft trouble. I think a V shaped deflector in line with the rod may be a cure IF you have bearing trouble. Your biggest challenge will be learning how to keep the Engine alive! You get a A+++++++++++ on your Project. Joe Ormonde.

[thirdstone]

So true , that case set has been retired now and you are correct about the twisted crank. That was the last failure on that case set. The Crank was welded at the time as well. I agree it is slightly madness modifying these engine so much , you sort of bounce from one weak spot to the next but what else am I going to do ? It’s a sickness !

[thirdstone]

Airbox coming along using plastic sheet and a heat gun.

[matt glascock]

Velocity stack!?!!! I love it. I diddled around with one for awhile, but all it had was a little mesh screen for filter which did essentially nothing. Do you think the foam will impede the air acceleration required to achieve laminar flow along the walls of the horn? Then again, who cares - it looks AWESOME. Hopefully you'll get some bonus screamin' reamin' air intake noise. You sir are certainly soldiering on in the highest tradition of Hodaka modifiers. I love it!!!

[thirdstone]

I just think it looks cool. But here is the rub ! I was tempted to buy a longer stack but I read that the shorter length is better for top end. I read that the stacks adjust the resonance of the inlet track but being a reed valve I don’t think that matters because when the reeds shut it stops the resonance through the carby, who knows ? Nobody will know it’s there except me and that will give make me grin a bit on the start line. Actually the Honda CR 250 Elsinore carb to air filter rubber boot is a valocity stack in design but that’s piston port.

[Bullfrog]

It is interesting to think about, "What are differences in air flow dynamics when the air-flow is reciprocating (mostly forward with small steps backward) versus intermittent (forward for a while, then full stop for a while)?"

While I have NO direct experience comparing the performance of a "pod" type filter configuration against a larger "ring" like filter (like the stock Wombat or Super Combat) . . . but I did stay in a Holiday Inn once . . . and I have been coached by tuners I trust that pods are simply more restrictive than larger diameter "rings". The air flow "wants" to come in from the sides . . . and the pod limits that because of its small diameter and the extended length simply doesn't contribute flow - cuz that flow from the outer end would be traveling where the small pink arrow is in the diagram. (Let the debates begin . . . )