Standard Bore on UL question

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Pete808
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Standard Bore on UL question

#1

Post by Pete808 » Wed Nov 28, 2018 11:11 pm

Hey guys. A month of two ago I ended up burning the valve on my 47UL. I sent the jugs to a machine shop here on island to get them taken care of. I need to replace the exhaust valve and 4 valve guides. The guy recommended boring the cylinder because he felt a "ridge". He measured the bore and said it is 3.353. What is the next size up? is it 3.40? If so does that mean I need pistons and rings that are 40 over? Sorry I am new to the whole bore size thing and want to make sure I purchase the correct parts to avoid further delay. thanks



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Re: Standard Bore on UL question

#2

Post by 1950Panhead » Wed Nov 28, 2018 11:24 pm

Standard bore for a 47 UL is 3.312"
.040" over is 3.352
.050" over is 3.362

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Re: Standard Bore on UL question

#3

Post by Pete808 » Wed Nov 28, 2018 11:30 pm

1950Panhead wrote:
Wed Nov 28, 2018 11:24 pm
Standard bore for a 47 UL is 3.312"
.040" over is 3.352
.050" over is 3.362
Thanks for the info. So do I need to buy .50 over pistons and rings and have them bore it to 3.362?

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Re: Standard Bore on UL question

#4

Post by RUBONE » Thu Nov 29, 2018 12:35 am

Pete, that depends on bore roundness, bore taper, and piston clearance. Your machinist needs to make that call, not us.

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Re: Standard Bore on UL question

#5

Post by 1950Panhead » Thu Nov 29, 2018 1:30 am

Thanks for the info. So do I need to buy .50 over pistons and rings and have them bore it to 3.362?
Probably, ask the man with the hone (or boring bar) if cylinders will clean up 3.362, as Robbie says he will know.

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Re: Standard Bore on UL question

#6

Post by Andygears » Thu Nov 29, 2018 1:35 am

Pete, since your confident in your machine shop to do the work, a discussion with them about what they recommend, buy the Pistons thru them and let them decide 50 or 60 over. Those are old cylinders, not easily replaced, and this may be their last rebuild, you want it done right by a good machinist who is committed to the package he is selling you.

Just my opinion,
Andygears

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Re: Standard Bore on UL question

#7

Post by Pete808 » Sun Dec 09, 2018 12:14 am

So I am having a tough time finding 50 over pistons. I ordered some from the Good Old Motorcycle Company but he just let me know that he is out of stock and so if his supplier. Anyone have any idea where I can get some? The guy at the machine shop also had no luck. I picked up some 60 over just in case because they were priced right, but would prefer to stick with 50 if I can.

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Re: Standard Bore on UL question

#8

Post by RooDog » Sun Dec 09, 2018 12:57 am

Is there any reason not to sleeve them back to Standard Bore size? I would have on my "50 Panny Project, but I could not find a shop who would source the parts and do the work too. Hell, If I want an idiot to do my work, I'll do it myself. So, anyway I bought new an aftermarket jugs, pistons & rings kit, and was done with it. I would guess there are no aftermarket suppliers of a matched set of jugs & pistons ready to load for your engine.
RooDog

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Re: Standard Bore on UL question

#9

Post by 1950Panhead » Sun Dec 09, 2018 1:32 am


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Re: Standard Bore on UL question

#10

Post by Pete808 » Sun Dec 09, 2018 2:25 am

thanks, I forgot about these guys

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Re: Standard Bore on UL question

#11

Post by kitabel » Sun Dec 09, 2018 3:30 pm

Is there any reason not to sleeve them back to Standard Bore size?
1. money
2. accuracy
3. higher temperature

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