Road Toad exhaust port bridge

[Strathbike]

Just finishing a restore on my 02 Toad . We've rebuilt the motor , fresh bore , relieved the ports as normal , but after reading the Hodaka book and the coments about the Toads siezing from new I'm wondering if they require further relieving of the bridge of the exhaust port ? I bought this bike about 23 years ago , very complete and original , but with damaged stator and windings . It has been an Australian delivered bike back in the day , and I haven't had it running yet .
Hope some one can give me some advise on this one .
Thanks , John

[hodakamax]

John, At least on the 99 Toads you will have to relieve the exhaust port bridge. Here's part of the bulletin I saved when I did one. I was able to take my measurements by pushing a ring in the bore and measuring with a feeler gauge. Have fun and hope this helps!

Max

[Strathbike]

Thanks Max , that's what I needed

[viclioce]

Is this a Mandatory thing, a necessary thing or just a recommended thing? I'm doing a Model 99 now and need to know. I remember Danny Cooke telling me about this when I was driving home from Colorado with the bikes. I was given a cylinder which was bored and a new piston to fit the bore. Does this apply to all RT cylinders or only after a specific oversize! And where do you get one of those stones? Thanks! ; D Victor

[Bullfrog]

It is a mandatory thing. Failure to relieve the exhaust bridge will result in seizure of Model 99 Road Toads, Model 01 Dirt Squirts and Model 02 Road Toads. You can make your own rounded corner stone - a little time at the bench grinder will do it.

Ed

[dcooke007]

Vic,

This is mandatory. I just use a medium grit aluminum oxide stone. Some applications with a bridged exhaust recommend drilling a couple of small holes through the piston skirt below the piston rings and aligned with the exhaust bridge.

Danny

[viclioce]

If the cylinder has been bored for oversizing, at what point does it become unecessary? Or does it always have to be done even if at .004 or .005? ; D Victor

[Bullfrog]

Since it is likely that no one has attempted to set up piston-to-cylinder clearance loose enough to eliminate the need for exhaust bridge relief, it is likely that no one can really answer the question. However, it is pretty certain that clearances would have to be loose enough to approach "worn out" (when new), so it couldn't really be recommended.

In addition, regardless of the piston-to-cylinder clearance . . . there is always the situation of the exhaust bridge being completely surrounded by "fire" thousands of times per minute AND only being able to conduct heat away to the cylinder wall at the top or bottom of the bridge. As a result, the exhaust bridge is hotter than the rest of the cylinder wall (tough on lubrication) AND it expands more than the rest of the cylinder wall . . . which causes it to deform. So the extra clearance is needed to help assure that the exhaust bridge and the piston don't try to occupy the same place at the same time.

Actually, relieving the exhaust bridge is not a difficult operation. The hardest part may well be working your attitude past the fear of doing something you may have never done before. It sort of spooked me the first time I did it. As I recall, you will be working with feeler gauges to do measurements - so, establish the clearance at the center of the exhaust bridge in a repeatable way. Then start your craftsmanlike hand grinding of the exhaust bridge - and check for increases in clearance as you work. It won't take too long to do.

Ed

[MTrat]

I've had luck with adding a lubricating/cooling hole in the piston as per Bultaco.

[hodakamax]

Does anyone have any advice on where to place these cooling holes and dimensions? I recently rebuilt a 99 RT for a friend and did the relief. It hasn't been started yet and if this is recommended I (or he) might try this. Thanks!

Max

[viclioce]

Now here's a good explanation, for those interested.....

"This is something common to any and all engines with a bridged exhaust port. Because the bridge is narrow it will heat up faster and expand more than the rest of the cylinder wall. It has no way to shed heat. As it heats it grows in all directions including inward toward the piston. When it does that the piston will seize at the bridge. Always. No matter the bore diameter or piston type. This is a function of metalurgy not motor design.

So it does not matter what oversize bore you have, failure to relieve the bridge by 0.003" or so will always cause hard contact with bridge and rings, and bridge and piston, and it will seize. The service bulletin was not some kind of field fix for a discovered problem. It was a notice to all of an added step in fitting pistons to new bores in engines with the port bridge in the exhaust port. It was probably left out of the manual, or by that time Hodaka was no longer publishing manuals and so issued a tech advisory, just in case someone didn't already know what to do.

So it is not optional and it applies always. If you are putting a new piston into an old bore, it should already have the relieved bridge. If bored ten over, the boring removes the 3 or 4 thousandths gap completely, and a new relief cut must be made. I would use a dremel and polishing abrasive disc, not a stone but in 1976 dremels were rare and stones were not. Stoning would take a long time.

For the most part, bore jobs are done by professionals so they would know already. DIY isn't commonly associated with boring cylinders, but so that everyone knew the need and how to do it, Hodaka published a bulletin. In case you get a cylinder back from a pro who missed the step when chamfering the ports, you will know to look for it as it is essential that it be done.

Seems no one gave you a complete answer. Hope this helps.

Greg McClintock
Prescott, AZ. "

[bchappy]

Victor, are you trying to pass yourself off as Greg?

[viclioce]

No Bill. Greg emailed me this response. He stays in touch with me via email. He's a great guy and always willing to provide me his insight. So I just copied the info from his email, including his signature block, and posted it here. Greg's answers always seem to have a lot more clarity to me. I value his many many years experience as a professional motorcycle mechanic and trouble shooter. And his answers don't just say yes or no. They provide experience and insight which I find downright helpful and clarifying, as well as refreshing. I would never attempt to impersonate him, just sharing as he has with me. ; D Victor

[MWL]

Victor, are you trying to pass yourself off as Greg?

I was thinking the same thing.....

[bchappy]

Good to hear from Greg again. Thanks for forwarding it Victor.

[viclioce]

Bill. Did you even think about how Insulting your comment to me might have appeared? It left me feeling that I had to defend myself and explain something which was clearly identified as a quote and the name of the quoted person included. I'm sure you didn't do it intentionally, but, please, consider how you say something in the future. How did my sharing a personal reply to me from a now quiet member of this forum, become something perceived as an attempt to pass myself off as that person? I can truly understand why Greg chooses not to respond here any longer with this type of posting being generated. It certainly left me feeling uncomfortable. Just saying. I always try to be honest with my posting. If the idea isn't mine I say so. I'm not the type of person who takes credit for other people's thoughts, words and ideas. And clearly, the wording alone demonstrates that it was Greg's words and not mine. Anyone who read Greg's postings often enough surely would recognize this as his, because his postings were undeniably his.

[bchappy]

My Bad. Please accept my apologies. I truly didn't notice the quote marks and I knew that you knew Greg and really thought you were adding his name because it was such a detailed explanation. Now, I guess I am the one that needs to stop posting as I may be hurting someone's feelings. Lets don't hash this out on the forum. My email address is [email protected] if you want to write me directly. Again I apologize. In looking back on it I can understand how it made you feel.

[motovate]

Back in the 80's I was a Honda MC Tech. At one of the Tech Schools I went to we were taught the stoning method to relieve port bridges. I also seem to remember a tech bulletin or a suggestion from one of the Traveling Honda Service techs that suggested using a Ball hone to not only cross hatch the cyl but also that the individual balls would walk into and out of the ports and have the effect of rounding over and relieving the port bridges. Honda also recommended using ball hones to cross hatch and even had it down to the grit and speed of moving the hone up and down in the cylinder. I do remember switching to ball hones and paying attention to the bridges. I suspect I would of used some feeler gauges to measure clearances at least to begin with but I don't remember any measurements that I made. I do remember never having any issues IE "comebacks" with bridge seizing so maybe it worked OK ------ or I just got lucky. That was a long time ago and memories are fleeting.

I'm curious what the Techs like Danny think about the ball hone method.

LBM

Vic,

This is mandatory. I just use a medium grit aluminum oxide stone. Some applications with a bridged exhaust recommend drilling a couple of small holes through the piston skirt below the piston rings and aligned with the exhaust bridge.

Danny

[viclioce]

Bill. I appreciate your last remarks. I don't think it needs to be said off line. I believe I handled it tactfully. Enough said. But thank you. I am the type of person who's tough enough to bust my knuckles and not cry! And I'm tough enough to handle something that may not have been intensional. But having spoke with Greg a lot about people on the forum who make less than friendly posts and then seeing something associated with what he told me, did set me aback a bit. No worries my friend. I trust in you! ; D Victor

[dcooke007]

Back in the 80's I was a Honda MC Tech. At one of the Tech Schools I went to we were taught the stoning method to relieve port bridges. I also seem to remember a tech bulletin or a suggestion from one of the Traveling Honda Service techs that suggested using a Ball hone to not only cross hatch the cyl but also that the individual balls would walk into and out of the ports and have the effect of rounding over and relieving the port bridges. Honda also recommended using ball hones to cross hatch and even had it down to the grit and speed of moving the hone up and down in the cylinder. I do remember switching to ball hones and paying attention to the bridges. I suspect I would of used some feeler gauges to measure clearances at least to begin with but I don't remember any measurements that I made. I do remember never having any issues IE "comebacks" with bridge seizing so maybe it worked OK ------ or I just got lucky. That was a long time ago and memories are fleeting.

I'm curious what the Techs like Danny think about the ball hone method.

LBM

Vic,

This is mandatory. I just use a medium grit aluminum oxide stone. Some applications with a bridged exhaust recommend drilling a couple of small holes through the piston skirt below the piston rings and aligned with the exhaust bridge.

Danny

I use a ball hone to resurface cylinder bores that are not going to be bored. I like the surface finish and the little balls do a good job of radiusing the port edges.......after they have been chamfered. I have not trusted ball hones to relieve the exhaust port bridge though and do not think it would accomplish that task. Using the proper size ball hone is also important for good results. Keep in mind ball hones purpose is to provide proper bore surface finish.

Max, I did note your question about drilling holes in the exhaust port side of the piston. I am using a Wiseco piston on a non Hodaka project with bridged exhaust and the instructions detail the task. Two holes centered on the bridge .060 - .090 inch diameter starting .300 inch below the bottom ring , .375 inch between the two holes. That should give you a good idea of the process. Interesting their illustration shows three holes though. Before performing this on your piston you should verify these dimensions will work before drilling. All good machinists, carpenters, craftsman number one rule is measure twice cut once. I also lightly chamfer the holes on the outer side of the piston skirt....on the inside also if I can get to them.

Danny

[hodakamax]

Ah, thanks for the info Danny. Road Toads were after my time in Hodaka history. I did rebuild one for a friend recently and was intrigued by the cylinder design. I kept thinking about what it would have been like to have that available in the early days of Hodaka racing. That large exhaust port would have been quite the advantage in the day but exhaust port bridges add a new problem. I'll probably not be building any racing RT cylinders, only dreaming about the possibilities.
Thanks again!

Max

[dcooke007]

Hey Max,
Here is a picture of the drilled exhaust skirt. You can see I drilled three holes instead of two.
Danny

[hodakamax]

Cool (so to speak) Danny! I would certainly do that if I was building another bridged exhaust engine especially for competition. Thanks for show and tell!

Max