Relieved exhaust bridge??

[two85atc250r's]

Is there a way that you can really tell if your exhaust bridge has been recessed? The machine shop I took it to said that when you bore it the bridge would recess on it's own. Is this true or is there something special that has to be done? How important is it that this gets done? The bore looks really good and the piston fits great, I just wanted to make sure they didn't ignore the exhaust bridge if anything needs to be done with it.

Also, does the chamfer need to be redone if you are only going up one size on your piston? The chamfer is the angles at the bottom of the cylinder that allow room for installation right? It doesn't look like the machine shop did anything there either. There used to be a tapered area that reached up into the cylinder a little ways but now that is gone. It is just smooth all the way down to those angles at the bottom. Sorry I'm a little ignorant here, this is my first bore job. Thanks for any help.

[machwon]

A relieved bridge has a different grain look than the rest of the hone/cross hatched cylinder. This is because its not done with the cylinder hone, so it wont look the same. You could also see the relieved area if you put a straight edge on the bridge. You will definetly need to have it done or you have a +99% chance of sticking that piston.

The chamfer on the bottom is not as important but you want to make sure all the cylinder ports have been chamfered to prevent a ring from snagging the port.

[regg187]

The chamfers are angles made on the horizontal edges of the ports, mainly the exhaust port. to allow the piston ring to get back into the area where there is cylinder wall after it bulges out(so slightly) as it goes up and down past the exhaust port(hole)
there is such a large area of off no cylinder wall in the exhaust port that the rings push out and they would snag the edge going up and down if not for the angles guiding them back in. That is why the exhaust bridge( makes 1 big hole into 2 smaller ones) needs to be releived to help guide and it gets so dam hot it grows more than the rest of the cylinder sleeve.

[two85atc250r's]

It definately hasn't been relieved then because the hone pattern on the bridge looks exactly the same as the rest of the cylinder.

So I guess I need to take it back then. Man that sucks. I just can't seem to catch a break on this rebuild. I just don't really know what I'm talking about when it comes to this machining stuff.
I will just try to tell him everything that yall said and see if he will be willing to redo it. How much does it need to be recessed?

Is it something that can be done after the bore with out much trouble? Or will the whole thing have to be redone? Thanks again guys for your help.

[two85atc250r's]

One more thing guys, the bridge looks like it is a little crooked right in the middle, like its pushed to one side. Does that happen from the bore spinning one way in there and is it a big deal? Thanks.

[machwon]

It should be .003" in the middle tapered out to the bore diameter at the top and bottom of the exhaust port. It can be done after the bore/hone job no problem. The crooked part is probably the casting mismatching the sleeve.

[two85atc250r's]

Thanks Bob, I'm gonna take it back to the shop in the morning and now at least I might sound like I know what I'm talking about. lol. Now I can give him an exact number for the recess. Man I tell you what, I don't know what I would do without this website. I really appreciate all you guys. Thanks again.

[wilkin250r]

Oh, man. If your machine shop doesn't know about relieving the exhaust bridge, or chamfering the ports, then you need to find somebody else.

No joke. I know you hate to spend a ton of money, and you REALLY hate to do things twice, but it really sounds like you need to send it to somebody that actually knows what they're doing.

It's not rocket science, it's not like you have to spend months trying to find the best in the industry, but it IS critical. It really does need to be done by somebody that knows how to do it. If your machine shop doesn't know about it (obviously, because they didn't do it) then they can't be trusted with it.

[Aceman]

I completely agree with Wilkin. If they don't know how to properly bore a 2 stroke cylinder the first time, what makes you think they'll do it right the second time?

Call your local cycle shop and find out who bores their 2 stroke cylinders.

[two85atc250r's]

I can always count on Wilkin and Ace to set me straight. lol. Thats the thing, this is the guy the Honda shop sent me to. Thats why I am so stumped. You would think he would really know what he was doing if he had all of Honda's business. They said he is the one who does all their machine work and he was great at 2 strokes. I thought that I made sure that I was really finding the best guy for the job. I am really not a short cutter and I try to do things right the first time. Now that I have already paid the guy I want it done right. Should I just bite the bullet here and go to someone else? Or do you think I can just go back and tell him what needs to be done? :confused: I dam sure want it right before I put it together. I've spent too much money on this rebuild to stick the piston first time out.

[two85atc250r's]

Well I bit the bullet and just took it to another shop. Yall convinced me I didn't want that guy touching my cylinder again. I found a machinist whose son races mx and I think he actually knows what he is doing. He knew exactly what needed to be done as soon as I took it to him. He's only charging me $25 to chamfer everything and recess the bridge. I thought that was well worth the peace of mind of knowing it was done right. Thanks again for saving my arse guys, I would have hated to install that cylinder without it being right. Now just cross your fingers for me that break-in goes well this weekend!

[wilkin250r]

Originally posted by two85atc250r's
IThey said he is the one who does all their machine work and he was great at 2 strokes.

This might be a half-truth.

It's entirely possible that this guy is great with 4-stroke bores. Consistent tolerance, straight bore, and always on-time with the jobs. He might be a great machinist, but it's the guy at the counter that says "Oh, yeah, he's also great with 2-strokes" because the guy at the counter has no clue about the differences. He knows he's sent a hundred bore jobs to this guy without any complaints, but he doesn't realize that each and every one was a 4-stroke.


Your logic isn't flawed. If my local shop told me "this guy is the best, we send him all our stuff", I would probably trust him, too. Good thing you double-checked.

[two85atc250r's]

Well I got it back from the other guy and it looks great. All the edges of everything are chamfered and the exhaust bridge has been recessed 3 thousandths now so I think I am in good shape. At least now I know who to take 2 strokes to. Glad I double checked the other guys work. Its a good thing I'm so particular about everything. I gonna try to crank it tomorrow so wish me luck!