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

[hodakamax]

Hey Danny, any maps, plots or illustrations of positions and size of these holes? I did the relief on a friends Road Toad cylinder and it hasn't been started yet. I might do the hole thing on it yet.

Thanks!

Maxie

[dcooke007]

Max, 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 exhaust 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 Cooke

[hodakamax]

Ah, thanks Danny, I may tear the RT engine down one more time and do the mod. I think you had some pictures quite a while back but I couldn't find them. Appreciate it!

Maxie

[dcooke007]

I could not bring the pick forward but here is the link.

Danny Cooke

viewtopic.php?f=1&t=1963&p=13422#p13422

[hodakamax]

Ah, thanks again Danny!

Max

[viclioce]

That's my cylinder for which Max reposted the picture. The light is a bit harsh from the iPhone flash. I intend to smooth things more with a stone. I've held off doing something with this cylinder until I know whether I need to bore it and go to a larger piston. May also consider the nicaseal option, which, I'm told, will make the cylinder surface much less susceptible to damage.

For now, I'll just use the 2nd cylinder I received from Danny, along with the piston/rings I already have. I'll use the cylinder in the photo for the second motor, or I may look for another cylinder as that might be less costly than having the additional cylinder work done. - Victor

[jakecb420]

@hodakamax....thanks for the insight and the keen eye. I was afraid that my work was not up to par. Live and learn I guess. Not that I won't attempt it again in the future, but I think I am gonna have the guy boring my cylinder take a crack at it. I plan to print out the bulletin, and hope he has the tools to do it(I'm sure he will). I'll try to post some pics of the finished product before I button it back up.

[Kels]

I am going to have to respectfully disagree with some of this..

The pic shows a relieved bridge , which is great.. Relieving it too much is not a good thing but there is no way to tell from the pics posted if the bridge is "over-relieved" or not..

What I have noticed with every Hodaka cylinder I have seen, is that the port champhering ,from the factory is almost non-existent.

I would highly recommend putting a very generous champher on every port, both top and bottom... This will aid in flow and help be more gentle on the rings..

The exhaust port in question is wider at the top than at the bottom. You can safely go to about 100% exhaust chordal width with respect to the bore size .. So if the bore was at 60mm than you could safely go to 60mm port width as long as the bridge as there doing its job. If the bride was not there you can go to about 71% before ring buldge becomes an issue. Point being.. the narrower chordal width at the bottom where it was mentioned there was ring marks, appears to be well within the limits. Keep in mind the narrower port width near the bottom has more contact with the rings and is helping them remain in place.

So, I will go out on a limb and say that any witness marks one thinks they are seeing are more than likely due to the lack of champher on the port vs any excessive relief in the bridge.

I would not go out and think the cylinder needs different bridge work until one looks closer and has done some measuring of some widths etc..

But in ANY CASE, put some champhers on those ports..

[hodakamax]

Since I don't communicate with Kels, I will tell everyone else that this loss of a piston was caused by too much relief and not enough ramp. To think this was caused by lack of chamfer (is how it's spelled) is silly. It's very obvious in Jake's photos that the top ramp was getting contact and the lower ramp wasn't. Not only was the ring entering the exhaust port but the lack of the lower ramp, or the angle of, doomed the piston ring assembly and pushed off the top of the piston. Chamfers are required but it was not the cause of this disaster. Missed diagnosis Kel.

Max

[Kels]

Since I don't communicate with Kels, I will tell everyone else that this loss of a piston was caused by too much relief and not enough ramp. To think this was caused by lack of chamfer (is how it's spelled) is silly. It's very obvious in Jake's photos that the top ramp was getting contact and the lower ramp wasn't. Not only was the ring entering the exhaust port but the lack of the lower ramp, or the angle of, doomed the piston ring assembly and pushed off the top of the piston. Chamfers are required but it was not the cause of this disaster. Missed diagnosis Kel.

Max

Max, The piston in this thread failed as a result of too much relief?? Not likely, the piston is MELTED.. all the ring buldge in the world will not melt the top of the piston... Sorry Einstein...

Melting aluminum comes from too much heat. Ring snagging does not cause crown heat like shown...

Maybe his oil is still in suspension...

[viclioce]

Tough room! Glad I don't work here.... ; P Victor

[taber hodaka]

The piston is melted? MELTED piston? All the ring bulge in the world will not melt the top of the piston. I cannot see any melted piston I only see a piston hammered to pieces and broken. My theory of relativity is that everyone is entitled to their thoughts, that we have different perspectives. I am not saying anyone is wrong and that only I am right. I cannot see with the eyes of others nor can you see with mine. And what does Einstein have to do with any of this Did he ride a hodaka? -------------Clarence

[Kels]

Please look more closely at the piston... It is melted...

Einstein's Hodaka.jpg (24.69 KiB) Viewed 5447 times

[Bullfrog]

. . . looks more like "media" blasted to me, where the media was chunks of piston edge and broken ring . . .

Ed

[Kels]

. . . looks more like "media" blasted to me, where the media was chunks of piston edge and broken ring . . .

Ed

Ed.. I could be but I don't think so.. The ring will not stay in the cylinder long enough to do that kind of damage..It would be nice to see a pic of the head damage.

We have seen this many times. The crown of the piston is melted due to heat.. Sure there are some indications of some foreign object bouncing around on top for a little bit.. but please look close at the crown.. You can see that it is melted as well

piston melt-3.jpg (8.15 KiB) Viewed 5440 times

image.jpeg (39.5 KiB) Viewed 5440 times

[hodakamax]

Gang, this is why I don't communicate with Kels. I don't have time to explain to him that what he says is melting is where the ring broke into pieces and beat up the top of the piston. Beating a dead horse Kels, give it up.

And Gang, I am a nice guy but I've been through this with Kels before. Done on this one.

Max

PS--Where's AZ when you need him!

[taber hodaka]

Are we looking at the same picture from the same angle? The opportunity is here to show deep respect to others, for their talent and knowledge. Leave the arrogance to others so they can boost their own egos. Off to see other threads-------------Clarence

[admin]

Clarence and my brother from my other mother (Rodney King) have the same idea...
"Can't we all git along?"
I have the utmost respect for all of you who have thoughts and ideas on what happened and how to solve it. All I ask is be respectful!!!!!
I am not going to mention names or point fingers but everyone is entitled to their opinions and can post them as long as it stays civil.PLEASE !!!!!

All I will say is whomever relieved that exhaust bridge with the dremel tool should not be a dentist. OUCH
Peace.

[hodakamax]

OK, back on the lighter side, even though I'm not Einstein, Al and I did discuss two stroke technology years ago. A silly joke from a crazy photographer friend from years ago. Seemed appropriate! Names have been changed to protect the innocent (Me). Long story.

Humor for the day,

Maxie

[Kels]

I am going to have to respectfully disagree with some of this..

The pic shows a relieved bridge , which is great.. Relieving it too much is not a good thing but there is no way to tell from the pics posted if the bridge is "over-relieved" or not..

What I have noticed with every Hodaka cylinder I have seen, is that the port champhering ,from the factory is almost non-existent.

I would highly recommend putting a very generous champher on every port, both top and bottom... This will aid in flow and help be more gentle on the rings..

The exhaust port in question is wider at the top than at the bottom. You can safely go to about 100% exhaust chordal width with respect to the bore size .. So if the bore was at 60mm than you could safely go to 60mm port width as long as the bridge as there doing its job. If the bride was not there you can go to about 71% before ring buldge becomes an issue. Point being.. the narrower chordal width at the bottom where it was mentioned there was ring marks, appears to be well within the limits. Keep in mind the narrower port width near the bottom has more contact with the rings and is helping them remain in place.

So, I will go out on a limb and say that any witness marks one thinks they are seeing are more than likely due to the lack of champher on the port vs any excessive relief in the bridge.

I would not go out and think the cylinder needs different bridge work until one looks closer and has done some measuring of some widths etc..

But in ANY CASE, put some champhers on those ports..

I guess I do not see how anything in the above 1st post I made is remotely disrespectful? PLEASE highlight the disrespectful portions so they can be addressed.

Thank you

[Bullfrog]

Um, I'm thinking the disrespectful portions of this thread started AFTER that post. I've got to ask - if all the commenting parties happened to be sitting at the same table in a Dairy Queen dining area looking at the photos under discussion, would the same comments be made?

Ed

[Kels]

Since I don't communicate with Kels, I will tell everyone else that this loss of a piston was caused by too much relief and not enough ramp. To think this was caused by lack of chamfer (is how it's spelled) is silly. It's very obvious in Jake's photos that the top ramp was getting contact and the lower ramp wasn't. Not only was the ring entering the exhaust port but the lack of the lower ramp, or the angle of, doomed the piston ring assembly and pushed off the top of the piston. Chamfers are required but it was not the cause of this disaster. Missed diagnosis Kel.

Max

Ed, I agree with you... The degrading comments started in the above post by the person complaining the most... Kind of ironic.. I just reciprocated the "kindness" which is only fair in my opinion..

As for the Dairy Queen question... My answer is yes... not sure on the others..

Back to the topic a little.. I think everybody should remember that once you break a ring, the engine will immediately cease to build compression and will "turn off" almost instantly.. so the only time there would be any ring or piston debris bouncing around on the piston would be from the residual revolutions of the crank after the engine shut off.. NO heat would be produced during this "wind down" nor would there be much pressure to embed the foreign material into the crown (especially the center portion) ..
I am still under the opinion that the crown in melted and this melting happened before and was most likely the cause of the ring breaking..

It sure looks like the port is plenty narrow near the bottom to adequately support the ring.. but until there are some measurements made, it is only an assumption.

[Bullfrog]

If the answer to my Dairy Queen question is "Yes" - - - I think we've identified a part of the problem. I'm just thinkin' that folks usually wouldn't and shouldn't talk to each other in that manner when face-to-face. So there is no excuse for it by long-distance over the internet. And one thing I learned from my wife - who was an Elementary School Principal for many years . . . I don't care who started it.

My two cents.

Ed

[Kels]

If the answer to my Dairy Queen question is "Yes" - - - I think we've identified a part of the problem. I'm just thinkin' that folks usually wouldn't and shouldn't talk to each other in that manner when face-to-face. So there is no excuse for it by long-distance over the internet. And one thing I learned from my wife - who was an Elementary School Principal for many years . . . I don't care who started it.

My two cents.

Ed

Ed that is a good way to think,for sure.

I was always taught treat people as you would expect to be treated.. If they still show disrespect... then return the favor.. different up-bringings I guess..

One is not better than the other IMO..

Give respect and you shall get it in return.

Give disrespect and you shall get it in return.

It is really that simple.

Fact is... we do not live in an ideal world.. and judging people based on internet public forums is highly INACCURATE IMO..

[Bullfrog]

Um, judging people and judging the behavior of people are two wayeeee different things. When the words issued ARE the behavior, judging that seems fair.

Back to the original topic - the chamfering did indeed not look good. AND, I have never personally examined a melted piston top which was all black . . . yet you have posted a photo of that exact thing. So, while I'm still a bit skeptical . . . I do have to rather seriously entertain the concept (which does go a loooong way to explain the "media blasting" in the center of the piston crown). Hmmmm.

So, when the engine in question goes back together with proper chamfering and proper exhaust bridge relief, there should be an engine leak test, precise timing check, compression check and cleaning of the pilot circuit in the carb to remove most of the likely variables which might lead to excessive heat at the piston crown.

Ed