Relieving the exhaust port bridge - a 41 year old mystery SOLVED?

[dirtsquirt80]

well heres my two cents just so happens last year Rick Mont , Mike Perrett and my self went and got some ice cream after the ANF ride last year in PA there was no name calling and I earned two great friends that day! so I'm on your side Bulldog.
As for the one piston with the black top and a hole in it well it just isn't right! wheres Rich Gagnon when you need him? lol

[BrianZ]

Looking at the picture of the piston in question, in my opinion it looks like it's been badly beaten up by pieces of ring in the combustion chamber. It doesn't look like it's melted. Since it's a two ring piston, I think it could have run for a while after the top ring broke. I won't say I'm certain but if there was money riding on it I'd be betting on the ring catching the port as the root cause.

[viclioce]

I'm still new to these machines. I had Kawasakis when I was younger. It's been my experience that when rings crack apart, they typically get blown out the exhaust port into the pipe. At least with my Kaw's. I haven't ridden a Hodaka long enough to find out if it holds true with them. ; / Victor

[hodakamax]

Hey Victor, a broken ring usually leaves the engine but not before dinging the head/piston/cylinder and can even work its way back into the crankcase. Always a bad deal. Have you had anyone check the clearance on your exhaust bridge yet? If the relief is over .004 " you can hopefully just over-bore the cylinder until the bridge is flush again and start over. Good luck!

Max

[MTrat]

Do other makes of motorcycles with bridged exhaust ports require the relief treatment?

[taber hodaka]

MT does MT stand for Montreal?? ------------Clarence

[BrianZ]

It could be Montreal, Montana, or opposite of full.

[viclioce]

Max. I'm going to take the cylinder to my local machine shop who's done some other work for me. I'm sure the gouging of the bridge is more than .004 and will especially be significantly more than that after any attempt to smooth it out. I guess I just let my exuberance get the better of me.

Then that means finding another piston as well. I'm going to use the second cylinder to finish the first one off. The one I bought from Danny. If it's not too bad, I'll use the first cylinder, after rebore, for the second motor. But having to go to a bigger piston will definitely make the costs for the second bike go up.

A question for you would be could I reasonably get away with using a set of .030 rings on a .020 piston, and if so, what would I need to do to adjust for it? ; / Victor

[viclioce]

Bought another RT cylinder today. Got it for a reasonable price, so I can hold off on the over dremeled cylinder until needed. I'll go stone on the new one as well as the one from Danny. At least now I can finish these two bikes.

Clarence, I curse you for saying "now you know what it's like for the rest of us!" ; D Victor

[MTrat]

Aha.. But the question remains; do other motorcycles with bridged exhaust ports require relieving of the bridge. And to Clarence -- MT means the same to me as it does to you, and for nearly as long...

[Bullfrog]

I'm not aware of any bridged exhaust ports which can get away with not relieving the bridge. So, in my experience (which is largely limited to Hodies), all bridged exhaust ports do indeed require relieving the exhaust bridge.

Ed

[Kels]

Again.. the bridge is only required IF the bore width exceeds the max percentage.. There are many engines that run bridged with no relief

[bchappy]

I was just wondering what causes the Hodaka bridge to heat up and expand into the piston and others don't. Seem to me that the exhaust heat is what caused it so how do other makes keep that from happening? Also, why would other makes install the bridge at all if the the port do not go over the percentage?

[Bullfrog]

Most of us vintage guys sort of accept that if the engine designer put a bridge in the exhaust port, then there was probably a pretty good reason at the time . . . and since most of us are running pretty much stock engines or engines tweaked to the "race" specs from "back in the day" . . . if there was a bridge then, there is still a bridge. We're not debating with you regarding when a bridge is required - but I do think the Toad exhaust port is wide enough at the top to require the bridge.

Interesting to know there are engines with bridged exhausts which don't require relief. I know Hodies pretty well, but not all those other engines. (It does make me curious about what design/operation parameters allow an engine to run with no relief of the exhaust bridge.)
Ed

[racerclam]

Lots of other engines with bridges have much more material in the bridge and protrude deeper in the exaust port , better able to dissipate the heat keeping the swelling at a minimum, also many are aluminum which dissipates heat better . And I relieve all of them .

Rich

[Kels]

Ed,

I think it would be interesting to have some measurements of the exhaust port (the entire port) on the Toad.. Then we can do some math and figure out if the bridge is really required.. any way you can get that info?

[taber hodaka]

Kels Again is like when we were little and were told, I told you once and now I am going to tell you again. I know you don't mean it, but the perception of arrogance kinda drifts in there. I don't know what you were doing in 1964 when we were learning by doing, without a manual or anyone to discuss our problems. It would be nice it you built a racer and let us see er fly at hodaka days 2017. Again we say on the hodaka bridge give it a little relief and recommend that you a stone and not a dremel. Hope to see your bike some day, where in Idaho??l -------Clarence

[Kels]

Clarence... My engine was already at Hodaka days 2016.. Many rode it.. there are even several threads on it here.

As for "perception" of "anything" I THINK you "perceive" what you want to perceive... and you like to try and find hidden meanings in my writings.

Ya know I could do the same with your posts and locate an "arrogance like" tone in your posts.

But I know better than to take too much credence in the written word on a public forum. Since the true "tone" of the writing can not be verified.

Could it be that I simply like to just get to the point vs. worrying about who might perceive an alternate meaning from something so simply and directly written???

Ask yourself, what do I have to gain by trying to HELP you guys with information (real world) on 2 stroke engines? Honestly, ask yourself and get back to me..

I think we MAYBE can agree that if what Hodaka was doing with their engine design in the 70's was that revolutionary, that they would still be in business today and all the other motorcycle engines would have incorporated that revolutionary technology..

Ya know sometimes it might just be better to leave all the perceptions and assumptions out and maybe focus on facts about people , as well as, engines.

Maybe more fair for everyone instead of trying to force one's perception on others? Possible?

[Bullfrog]

I may have a Toad cylinder around here somewhere . . . but doing the search for one and measuring it is well behind some other higher priority items on my plate right now (like seeing if I can stabilize the coil windings on the coil cores of my 40+ year old ignition system and return the scooter to service).
Ed

[Kels]

I may have a Toad cylinder around here somewhere . . . but doing the search for one and measuring it is well behind some other higher priority items on my plate right now (like seeing if I can stabilize the coil windings on the coil cores of my 40+ year old ignition system and return the scooter to service).
Ed

Ed, understood.. No problem, just an idea based more out of curiosity than anything else... Maybe keep it on the back-burner for after you get your coil issue resolved

[taber hodaka]

Kels Sorry about the ignorance of my arrogance. Sorry if I offended anyone including you.

I think if it had not been for hodaka in the 60's we would still be driving puchs.

I thank and enjoy everyone efforts and contributions, wasn't Maxes project just awesome?

And you Kels making a wombat reach 80 miles an hour is just unbelievable.

There are people in awe about how well your scooter performed, I hope I get to share that ride sometime.

If it weren't for beginners needing information there would be no reason to offer help.

I am glad the forum offers us the opportunity to show respect and admiration to others for the shared projects and knowledge.

I will strive to be more upbeat, positive and tolerant of others.

I would prefer to knock on the door and share a cup of coffee than email, phone or write. I would like to meet you sometime and see the shop with respect Clarence 406 261 9326 Columbia Falls Montana

[hodakamax]

Clarence, I hate to admit it but you are a nice guy! (And you are darned funny--my kinda guy!) Make sure the new #27 house numbers are on and I'll put you on my Bucket List of people to come and see personally. I'll try to arrive during zucchini season so I can bear gifts.

Maxie

PS--I hope you haven't worn out those knobbies I sent up there for our ride you promised me.

[racerclam]

The Toads as well as late Rat is 41mm and in fact needs a bridge

Rich

[hodakamax]

A few years back I rebuilt a Road Toad engine for a good friend. Road Toads were after me in the Hodaka shop business and I was my first peek at the workings of a RT. I was amazed at the exhaust port design and the Aluminum cylinder and its heavy duty construction. Having built lots of 90/100 Hodaka racing engines in the day we enlarged the exhaust ports as much as we dared (or what Harry T. said we could get away with) before the ring would set up its deadly oscillation into the exhaust port. I kept looking at the RT cylinder and dreamed about what it would be like to have cylinder like that in the old racing days. So much for dreaming and I rebuilt the engine as per the old days. Only after the engine was mounted in a town far far away did I start reading about exhaust port bridges and quickly "recalled' the engine for the needed modifications. Not the first time I've had to do something twice! Anyway, all is well and I'm further educated about exhaust port bridges and have that modification under my belt.

Just another story,

Maxie

[viclioce]

I rode a Puch once. It was a test drive. I read an article about them and tested one in ABQ after moving back to NM from NC. Got it on the makeshift track behind the shop and the throttle stuck, wide open. Started feeling the bars for the kill switch until I remembered what the article said about the kill switch being hidden under a cover below the seat! Downshifted hard through the gears got it into second and brake slid it to a stop. Rolled the bike back and said "no thanks!" ; D Victor