Case Reed 125 Hodaka Project

[thirdstone]

Nice Photo
I’ve checked a Yamaha parts fiche and they list the same Rod and Bearing for both types of pistons , no spacers.
It must be okay .

[Dale]

I did find pictures but not the discussion on this subject. As I remember both Wiseco and Harry Taylor in the day did not consider this a problem. Although this looks scary the rod is always centered with needles on the rod and all seems to be self centering. I ran the set-up on the right with no problems so far. I'd get more opinions on this as really don't want anyone to run an engine like this on my word. There are even spacers for this set-up if it worries you and I think Strictly Hodaka had them at one time. Maxie

I am running a Combat Wombat with a newer style Wiesco piston (+.050) without spacers. No issues.
At the time of assembly, I believe that Paul had spacers for the 100cc pistons but not the 125's. Conversations led me to go for it and all seems fine. It does make me wonder about comparing my stock motor to Kevin's fire breathing work of art...

[thirdstone]

Just kicking back enjoying a nice Australian Reisling and contemplating what to do.
I can make the Yamaha piston work . It needs a special pin (which I have) but it also needs about 1mm taken off the head to get squish back to acceptable spec. 1 mm off the head gives 50 thou squish with a 10 thou copper gasket.

OR I could use a piston port dykes ring Hodaka piston and cut the rear skirt and just accept that the slot is there.

It’s a one way mod if I go ahead with the Yamaha piston. They are wAy cheeper and easier to get than a Hodaka piston but a lot of work and I would like a tighter squish .

Nice wine at least.

[Bullfrog]

Decisions. Decisions.


Hmmmm, I recommend another glass of wine.

Ed

[gearyoliver]

You get the BEST advice in this group!

"Hmmmm, I recommend another glass of wine."

[matt glascock]

Third, if you have time, how do you determine the squish area that best meets the demands you'll be placing on the motor? At 50 thou, is your goal focused primarily on screamin' reamin' top end? Also, what is your compression goal and what type fuel are you tuning for? Thanks!

[thirdstone]

Third, if you have time, how do you determine the squish area that best meets the demands you'll be placing on the motor? At 50 thou, is your goal focused primarily on screamin' reamin' top end? Also, what is your compression goal and what type fuel are you tuning for? Thanks!

Matt I’ve used 50 Thou before with a 20 thou head gadget . That allows going to 40 if I want to use a copper 10 thou gasket. Yamaha race tuning sheet for YZ 125 said to use 30 Thou. In any case the tuners I take note of all say go as close to zero as rod stretch will allow.
Now squish is not compression !
For compression over the years I’ve gone from stock , around 170 with my gauge to 198 PSI
But now I like 160 . The high compression engines felt great down low but didn’t rev out like the low comp ones. Maybe I should have backed off the advance with the higher comps because the higher you go the more prone to detonation you are. I run a PVL at 2.2 mm , I’ve run it up to 3 mm and to be honest I couldn’t tell you there was any notable difference. I use 98 octane pump gas , I’ve never tried race gas .
Interestingly the low comp head I use I think is an 03 Head. I use it with a 10 thou gadget and I’ve cut grooves in it. The engine flat out screams with that head. I say I think it’s an 03 because it’s hard to identify. I originally it bought over the internet by mistake thinking it was a 97. I never used it without the grooves. Funny story, I was testing the bike and I noticed that it was running better than I remembered so I left it and raced a few meetings. One day I was stripping it for regular maintenance and I noticed the head was the grooved one. I thought I had the 97 head on but I had mixed them up and fitted the wrong one. A happy accident. That’s how I was introduced to low comp.
Max RPM target is 9800. That is about all the Hodaka engine can take without flying apart. I have tested / raced my engines with a tacho fitted and that is where it gets to and stops accelerating. This tells me that is where the port timing and pipe max out. I can verify that at these RPM these engines feel like very busy.

This is where the clutch gears cop a hiding carrying a 900 gram clutch .

Putting the clutch on the main shaft like Lee Fabry did is the only answer to this I feel.

[matt glascock]

This is great information, Third. Thanks so much for taking the time to offer your rationale. I dig the "happy accident". I have a M94 that I'm pumping up so your experience here is applicable. One more likely stupid question. Are the torque grooves you cut into the combustion chamber dome volumetrically significant when tuning for compression? I was considering tuning for 105 octane race gas/racing castor at 20:1 which is what I run in my TM at ~182 PSI, but you've got me thinking that I can get out of this 94 what I need without turning it into a one-moto wonderbomb. Great stuff here, Third. Thanks for sharing.

[thirdstone]

Hi Matt
I have no problem sharing I wish more people would do it. There is too much secret BS. In the vintage world. What is really refreshing is that THE MOST successful Hodaka tuner MR Taylor was very free with his thoughts.
Of course the grooves have volume but quite small
I don’t think it would make a big difference.
Notice I didn’t groove the squish band .
The Volume shown on the head is the CC volume with plug fitted and without head gasket . I didn’t ever do this without grooves .
I must be very clear here because this groove thing is quite controversial. I don’t know if they are an improvement. I did read some time ago that a tuner I know ( name withheld) noticed a 500 rpm increase in idle with fitting a grooved head. That to me showed more efficiently burnt fuel. I have not noticed any detonation however like I said I run this head a fairly low compression.

[thirdstone]

For comparison my radial head is 13.5
CC and s 97 head is 12.5 CC

[thirdstone]

So you are pumping up a 94 .... that’s where i started and continue. Some quick comments , excuses me if you already know this.
Convert to Reed and get someone ( or yourself) to reshape the exhaust port and raise to 97 spec
Sort out your head to match.
Find and fit a 97A gear set
Go to straight cut primary gear.
A stock reed manifold with KX 80 dual stage reeds work well Boyesen part number 646 is a good start.
Fit a good pipe and you are almost there. Carby size from 30 to 34 is my pick.
A4 plate clutch will handle that no problem and make your engine more responsive.
Go to CDI for even more snap.

If you can get a 97 cylinder and head then you will save a lot of work , still need to widen the exhaust port
An 03 cylinder / 97 head is also very good once the exhaust port has been changed.

Of course there are more things to do after all that but it’s a great start.

[matt glascock]

Awesome info, Third. Here's where I am. Mild port work. Exhaust port raised. I'm still on the fence regarding conversion to reed induction. I don't mind if its a bit pipey as it will be campaigned exclusively on VMX tracks so it should be easier to keep on the pipe compared to woods work, etc. That said, while the motor is apart, now is the time for port work. My toaster tank SR is ported for reed induction and it totally rips. It has a VM 32 on it right now so it sounds like I'm in range. I have a competition Only Torque 125 pipe that should still work even if I up the ante at the porting table. It has a close ratio gear set on it now. Great suggestions, Third. Thanks for taking the time to share.

[thirdstone]

Matt no problem

I’m thinking you are on the iron cylinder 94.
I have no experience on the piston port design having said that , Honda CR 125 Elsinore is piston port and they haul ass.
There are some things that will cut lap time as much as any porting.
Ditch the 30 mm forks and the 94 front wheel. Bigger forks like the TDog 34 mmm jobs and a conical hub from a later Hodaka with drop seconds off your lap time. While you are at it get rid of the 94 sprocket carrier . It has one bearing on the inside , that caused me a DNF . I fitted a later carrier that has two internal bearings .
Your airbox wil need to be changed as it will suffocate your engine .
It’s hard to rectify because the 94 frame doesn’t have the down tubes to frame an airbox.
I did have an aluminium box made but it cost a lot. A uni filter POD as big as you can get will help as long as it doesn’t rain . An airbox is better.
In my opinion The stock swing arm is too short . I have two arms , one 1.5 inch longer the other 2 inch. Surprisingly this makes s big difference. My internet friend Jim Stein put me on to some cheap tyres that work really well because they are very lightweight.
Kenda 100
59m k760 track master
K3173
P/n 047601807C0
I once fitted Michelin star cross 5 100 tyres . They kept flicking the chain off. 100 is not always 100
I had to trim them with a razor.

[matt glascock]

Yes, Iron cylinder 94. I'd love to find an alloy cylinder with a good bore or three left on it but they are getting scarce. Ditto the forks. I'll probable try to squeek out a bit more travel and reinforce the 30s. I had an 03 front end but I (hate myself) traded it for a motor. The search is on for that in earnest. I will look for the Kendas. In my humble opinion, don't mind the narrower power band of the piston port motor. For woods work, absolutely. I'd like to get a still air box fabbed. For now I'm running a stock 94 air box with a bunch of holed drilled trough the inner cover and the snorkle aperture opened. I'd love a box like yours, but I don't know if I have the juice to fab one that nicely. I'm looking at a late model RT roller so that would answer the conical hub question. Thanks again, Third.

[thirdstone]

Matt that might be your answer.
Check the parts listing , it might have the stronger sprocket carrier as well.
Is the swing arm longer and use the same method of fitting?
Someone here might know

[matt glascock]

Oh, the swing arm has been extended 2" and braced. I forgot to mention that detail. That makes the 94 adequate for the project. It was just too hard to keep the front wheel on the ground before that mod. I've extended the swinging arms on all my race Hodies.

[Joe Ormonde]

The cheapest way to get more clearance or lower compression is to custom make a THICK Base Gasket. You can buy Gasket Sheets in several thicknesses. That`s the method of my madness! Joe Ormonde.

[thirdstone]

A quick way to change your port timing as well Joe

Cheers

[dirty_rat]

Matt,
For forks, you can look at other brands besides Hodaka for 34mm forks (as long as you have the proper triple clamps). Quite a few Japanese bikes in the mid to late 1970's had 34 mm forks (almost all made at the same factory, only differences were the spring rates and damping rates). Look around at some salvage yards or on e-bay and you can get them rather inexpensive. Some of the other brands triple clamps even work. A friend had a set of early Yamaha YZ 250 forks that bolted right up to his Hodaka. Worth a look around.

[matt glascock]

Thanks Dirty! I'll check it out. 03 Forks are impossible to find these days. I wonder how many sets I've crossed paths with over the years and said something brilliant like 'I'll never need those'. I've heard that Kawasaki forks will fit. I have the frame reinforced, but I would like to beef up the front end as I plan on racing this in open class. On it. Thanks again!

[olddogs]

Mid 70s Suzuki TS 250s used 34 mm forks that bolt right on and accepted Hodaka conical hub wheels and axles. If I remember they are totally different on the inside and used a shorter spring with a spacer tube. They fit great and I believe were softer than the SL 250s by quite a bit, but no internals interchange.

[matt glascock]

Hey old, Good to know. I have a bud with an excellent Suzy parts stash. I'll give it a look-see. As I recall, the TS line were not particularly light bikes. I bet you're right. The softer ride must be due to a different design principle as opposed to simply different spring rates. I will look into the travel of the TS.

[thirdstone]

Matt if your are racing mx at anything intermediate and above changing the forks and brake are a must.
Renown Hodaka racer Jay Lael uses 74 Honda CR 125 forks with great success. I’m pretty sure they are 30mm . Not quite as stiff as 34mm forks but way lighter.Ive riden a mates Elsinore that had the
Elsie forks with race tech springs and emulators and they were pretty good. The brake was bad though. Just another option for you.
I’ve got Honda 35 mm forks and triple clamps on one and Husky 35mm Forks on another . Plenty of 35mm forks out there .

[matt glascock]

Any head tube mods to get the Honda triples in play? They are way easier to score than the Husky set-up. Thanks Third!

[olddogs]

Just in case their are some "new" to Hodaka members following this discussion, its the triple trees that cause the hurdle when trying to upgrade forks. All of the big 4 bike makers, Honda, Suzuki, Kawasaki and Yamaha used tapered bearings in the frame head, where Hodaka used what I like to call the loose ball bearing style. I call it this because sometimes you remove the triple tree and the bearings run loose in your garage. Bill Cook contacted me years ago and was looking to develop a tapered bearing conversion kit if enough guys were interested, but I never heard if any progress was made.