The Hodaka Club Forum

I see ports that need matching, a slot for conrod clearance, overall length. More than you can do with a hammer.

Started the port matching . A test along the way to check flow direction in the new rear side ports using the good old water from a tap method.
I’ll make sure the flow from both sides is even and clash head on.

Boost port going in . I’m using the existing roof for the angle.

Standard sleeve only sticks out 20mm from the bottom deck.

Yes that will get trimmed later , quite a big job I keep putting off.

After a bit of adjustment I have the boost port flow where I want it. Before the flow was spraying all over the place, the transition from virtical to roof angle was instant causing the water to splash. Now I have a curve transition and it’s way more of a stream.

More flow testing. One error now evident is that I put the transfer bridge in the middle of the transfer port. I should have biased it towards the exhaust port. I was planning to put a web in the transfer for more flow direction control. I’m not sure that is now possible. BUT I’m quite happy with the resultant flow direction as it is.

Notice how the two flows are seperate occupying different areas of the bore and biased to the rear of the cylinder. This should ( I hope ) stop the gas shooting out of the exhaust port and there by give a wider power band. The pipe pulse will still pull gas out (desired) but it should be reduced a bit.
The flow from the opposite ports will clash head on reducing the kinetic energy , that’s the theory anyway.

Enjoying each and every update!
Ed

I'm with you, Captain! Of all the awesome build threads on our forum, this one is among the very best.
Thanks for sharing this really cool project, Third!

Thanks for the kind words guys it gives me motivation for days like these.

Cutting off the sleeve and making the spigot. All hand files and hacksaw.
Not Fun at all .

I would suggest busting out the Dremel, but Captain Eddie would yell at me again.

A bit of an update, the Spigot is completed . Matched to the cases and ready for a bore when I get the piston. All down hill from here.
I made a bit of a boo boo with some porting rash at the back of the boost port but I’m sure I can deal with that.

A bit excited now. I have my piston delivered so now I can get the bore done and finalise porting. Next step engine assembly so we are close.

I selected a Yamaha piston as it met the design requirements without getting attacked by a grinder. I don’t need any holes in the back of the piston in fact any hole would interfere with the boost port design so that’s why I’m not using a Hodaka piston. For a while I was going to use a 95 piston, I even bought one but the slot bothered me and I would have to chop off a lot on the rear skirt.

Yes, I'm watching!

What Yamaha piston did you use that had a 15mm piston pin hole and the correct pin offset from the top of cylinder? Inquiring minds would like to know!!!

Thanks

Just when I thought it was going well I hit a snag. The piston I bought is not what I thought it should be. I bought an 88 YZ 125 piston however it’s not what I need. I have just seen the boss area and it’s too wide. I bought a box of used YZ pistons years ago , I don’t know what years they are but one of them fits close enough to use . I might need to recut the dome of the head depending on what I find squish and compression wise when I have it assembled. So today - not happy.

Some piston comparisons, Hodaka V yam
And yes the YZ piston uses a 1mm wider pin.

I have a special step down pin to adapt the YZ piston to the Hodaka little end bearing.

Here is my problem

dirty_rat wrote:What Yamaha piston did you use that had a 15mm piston pin hole and the correct pin offset from the top of cylinder? Inquiring minds would like to know!!!

Thanks

The piston I bought was a Wiseco 559PS 86-88 YZ 125 however Yamaha has changed the pin boss thickness reducing it, I didn`t pick pick up on this until I had it. This leaves too much room for the little end bearing to move around side to side, that`s what I think any way. The piston I`m leaning toward now is one from a YZ / MX 125 from 74,75,77 Yamaha Part number 401-11631-00-96 ( the one in the picture above) for a Standard piston. The crown distance is between 0.5 to 0.75 shorter than a Hodaka ART piston. It will need an adjustment to the head which I`m prepared to do.
Earlier on I looked at ways to adapt the Yamaha piston and one of the options was a rod swap. I spoke to my machine shop and they were confident that they could get it done, I`m starting to wish I had done that.

This was discussed quite a while back about about extra space on the pin between the piston boss and upper rod bearing boss. I don't think there is anything to worry about in this case as the rod seems to self center on the pin. Maybe the Gang will have some more input on this. Meanwhile I'll try to find the discussion. Maxie

Maxine that’s interesting, I’d love to read that. At the same time I should research if Yamaha changed their rod and bearing as well. That might be the answer. It’s certainly looks like it could be a problem but hey what do I know !
One thing I do know is they changed the ring pin location to centre rear, that is s problem for me as it’s right in the muddy of the boost port . It would be nice to not have to move the pin every time I change s piston.

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