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Discussion Starter #1
So I have two cylinder heads. One came off a rust bucket of a motor and is pitted from rust. I took it to the local shop and they said that I should have it bored to another size so oil doesn't get trapped in the pits and cause it to smoke. I have another head from my running motor that when it was dismantled, the piston was scratched so I'm assuming the cylinder wall is scratched also (would post pics but don't have any yet) which I am also assuming will need to get bored. Was hoping to get away with a hone as I ordered a stock piston and should be here in the next couple days. Since I will more likely have to return the stock piston...which oversize should I buy? was thinking of the 70mm so no other parts have to be purchased and wait another 3 weeks for the parts to arrive.

What would you do?

Cheers!
Jim
 

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Generally ,you don't bore any more than you have to ,because if you go too big ,the next time you have to do it you can't and you must replace the cylinder or sleeve it .What does the machine shop say ?
 

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Just for clarity sake, you are talking about the cylinder, not the head. As Bruce said, normally you don't bore any more than needed to clean up the cyl. Stock bore is 67mm. As an example, machine shop bores to 67.35mm to clean up score marks. Next oversize piston from Yamaha is 67.5mm. The shop would bore and finish hone to that size. (The actual measuring and fitting the piston to the cyl. with the proper clearance is a little more complex than that, but that 's the basic idea.)
 

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Discussion Starter #4
I haven't had time to take the other cylinder in. Shop said to bore the pitted one but never said what size to get
 

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Discussion Starter #5
I will see what they say but the pistons the sell are $80CAD more expensive then if I went with oemcycles. Made the mistake of ordering a stock size not thinking it might have to get bored. Live & learn, trial by error seems to be the theme of my project...all good though
 

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The shop needs to examine the cylinder closely to determine what size they need to bore it to in order to get past the pitting. They will need a list of available piston sizes from you so they know the different target sizes.
 

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One can get away with a lot less than perfection on a cylinder. Some glaze breaking and a new set of rings on the original piston and this engine ran like a champ as witnessed by the NorCal Nut Jobs. The bike was mine but Big D rode it for many trouble free non oil burning miles.

P3080845.JPG

If you are going with a new piston may I suggest a Wiseco. They come with new rings and wrist pin and clips. They are forged, therefore very strong, and are of higher compression than stock.

I forgot to add that if you will settle for a really inexpensive 70mm cast piston and don't mind waiting the week or two it takes to get here this is a good choice.

Piston Rings Pin Clips Kit For Yamaha XT225 XT 225 STD Standard Bore Size 70mm | eBay
 

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Discussion Starter #8
Wow, thats an amazing price. I have a wiseco 67mm coming any day now but that was before the shop told me i need to bore because of the pitting and how oil can get in the pits to make it constantly smoke. The other cylinder i have, the guy that is working on the engine said i should get it ball honed because of the scratches. I will try and post pics here shortly.
 

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Discussion Starter #9
Here is the scratched piston and cylinder of the rusty/pitted one
 

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If it were me I would use that cylinder. Hone it for sure, ball hone or cylinder hone, just enough to clean up most of the surface. Also, if going with the 67mm Wiseco, the piston to cylinder wall clearance should be .0025 inch. If it were mine I would make it .003".

Your piston looks like it overheated and expanded and scraped the cylinder wall. Aluminum from the piston sticks to the cylinder wall and looks terrible! Reality is you can clean it off and the cylinder is in good shape. Steel is much stronger than aluminum and the steel usually wins. BTW, increasing the clearance to .003" is to allow for more expansion.

Be careful changing plans. Most of the time that only leads to delays and more money being spent. Good luck. Tony
 

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View attachment 99969

And here is the scratched one
That looks worlds better than the cylinder I showed. I think once you clean the aluminum up and hone it and and get the correct piston to cylinder clearance it will work fine.

You can check the clearance using feeler gauges. Not real accurate but it works.
 

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Discussion Starter #13
Thanks for your insight Tony, I really appreciate it. I will be picking up the cylinder tomorrow from my engine guy and dropping it off at a machine shop and see what they have to say. I will ask them to go to .003 as I trust your expertise. You are right about the delays and more money being spent. I am crossing my fingers that the cylinder is okay and my piston comes in PDQ. The piston and front/rear blinkers are all I need to take her on her maiden voyage, after the sanding and painting of the frame and plastics. It has been almost a year getting parts/dealing with setbacks, being a new father and a lot of doubts about rebuilding this bike...but I can't wait to get this thing on the road and start with the next journey of a tw/ttr conversion. Everyone on this forum has helped out a great deal and it is greatly appreciated. Sorry for getting sappy, it's late, I'm rocking my baby boy to sleep and thinking I can't wait until he is old enough to help me work on the bikes. Who knows, maybe one of these tw's will be his one day as his first bike.
 

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for the six diff engines i had honed i drop of cyc and they measure and supply piston of your choice and they fit that piston to that jug..... usually for a very good price....this is a engine repair shop.....
 

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Discussion Starter #15
Apparently I am supposed to wait until the piston comes then he will check the clearance but he said best option would be to bore it to the next size up. Wish I would have done more research instead of just pulling the trigger and buying the stock piston.
 

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Apparently I am supposed to wait until the piston comes then he will check the clearance but he said best option would be to bore it to the next size up. Wish I would have done more research instead of just pulling the trigger and buying the stock piston.
I detect a lot of regret here. Maybe you would be better off returning the piston for a larger one. It will be time and money well spent.

I may not have gotten the clearance thing quite right -- make it .0005" larger than the minimum. If the minimum is .002, then make it .0025. If the minimum is .0025, then make it .003. It should say on the outside of the box what the minimum clearance is. It has been a while since I honed a cylinder for a larger piston.
 

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Discussion Starter #17
I think that is what I will have to do. I havent received the piston in the mail yet so i cannot look at the box for the clearances. I think i will return it and have to wait another 3 weeks to put the motor together.

" Waiting is the hardest part."
Tom Petty
 

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Discussion Starter #18
Got my piston and the clearance is 0.0020. Can anyone tell me the maximum they can bore until for the piston to work?
 

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Got my piston and the clearance is 0.0020. Can anyone tell me the maximum they can bore until for the piston to work?
.0020 in the minimum clearance. I bet you could go .004 or even .005 and it would still work OK though I bet you machinist will be against it.

The question is what is the diameter of the piston measured at the bottom of the skirt minus the diameter of the cylinder? That is the clearance.

You can get a rough idea with feeler gauges but it scratches the piston -- the scratches are harmless but I bet it won't be accepted as a return if it is scratched.

The place to measure the diameter as told to me by Wiseco:
PA280036.JPG

One can then put the piston in the cylinder and measure the clearance with a feeler gauge. It is not very accurate but you can get a ball park idea where you stand.
A couple of things to keep in mind. The feeler gauge is flat and the cylinder/piston is round so there will be resistance from that. You don't want to strong arm the feeler gauge into place -- it should simply take up the excess space. In the picture it isn't being measured at the widest point so the measurement will be a little bit large -- it is actually about .0028 and if I pushed the piston in with the feeler gauge where it is the feeler gauge would be wedged tight in place -- which is no good.
PA280034.JPG

Best bet is take it all you your machinist and let him measure it with micrometers then make you decision what to do.

And another picture just for the heck of it. This one and the ones above are a 71mm Wiseco piston in a 223cc cylinder. I thought it looked pretty so I posted it.
PA280031.JPG
 
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