The gasket surface on the 447 cylinders is wider, but the 256 head will mount and seal.
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256 vs 447 motor differences
- Thread starter Mailman
- Start date
Aren't the gaskets different thicknesses? How do you handle gasket thickness when putting a 256 head on a 447 cylinder?
I was asked the same question,maybe the same member
use the 477 gasket and copper coat several times and let it try before using. The only difference if it's a XS1, the combustion chamber is slightly smaller in cc volume,intake ports are different other than that,it'll bolt on. I did a XS1 head years ago and this person did the exact swap.
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Like Jack says!
I don't recall a difference in thickness, Dawg, but it's been awhile since I had my hands on a 256 motor. If there is a difference, it's less that the difference between OE 447 spec. (.047") and the .060" Athena gasket that guys keep using. If it was my money, I'd use a Vesrah .047" gasket, a .040" composition gasket from Ottoco, or, depending on intentions and how things measure out, a custom thickness from Cometic or Copper Gaskets Unlimited.
I don't recall a difference in thickness, Dawg, but it's been awhile since I had my hands on a 256 motor. If there is a difference, it's less that the difference between OE 447 spec. (.047") and the .060" Athena gasket that guys keep using. If it was my money, I'd use a Vesrah .047" gasket, a .040" composition gasket from Ottoco, or, depending on intentions and how things measure out, a custom thickness from Cometic or Copper Gaskets Unlimited.
Thanks, that explains a lot. I have acquired a lot of gasket sets in boxes of parts over the years, and the head gaskets all seem to be about .060" plus or minus. Even the vintage Rocky parts gasket set above, which is labeled XS1, has a .060" head gasket.
And yeah, I'm asking for that same new member. He's restoring an XS1B, but has a bad leg, so is putting an electric start motor in it. He wants to retain the correct look as much as possible, so he bought an XS1B head and head cover from me to put on the electric start motor.
So I guess he couldn't trust me on my word even after I consulted another member for fact checking as to not mislead him in any way.
I guess more aftermarket suppliers than Athena made .060" XS650 gaskets. The reason is cost: .060"=1.5 mm.=cheaper standard stock. I won't use that stuff.
No, please don't blame him, blame me. I was double checking because it all didn't make sense to me. When it comes to how these things measure out I'm totally lost. I am under the impression that the 256 combustion chamber is smaller than the 447, so I don't know, I thought maybe using a thicker gasket to compensate made sense.
Anyways, not my problem, I'll shut up now.
Anyways, not my problem, I'll shut up now.
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I'm good on my end. The 256 had a compression ratio of about 8.8 I think and yamaha cut a 45 angle to reduce the chamber by a few CCs to lower the compression on the 477 to 8.4-8.5. I personally would use the better quality Vesrah head gasket,coat it and be done with it as that little bump in
compression wouldn't hurt and cam timing would be in check.
here are the head gasket differences. use the 477 HG when mating the 256 head to 477 block.
256 left 477 right,bore remains the same
256 left 477 right,bore remains the same
Thank you. I completely misunderstood the reason for coating the gasket. It all makes perfect sense now.
As always the Borg has the answer!
Jack I got asked, and steered him to you (and 2many) cuz I hadn't done it. I then threw the question up here to illustrate how asking a question in a thread often results in better (or more complete) answers.
Jack I got asked, and steered him to you (and 2many) cuz I hadn't done it. I then threw the question up here to illustrate how asking a question in a thread often results in better (or more complete) answers.
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And here are a couple of reasons to use Permatex copper spray when you coat the gasket, Dawg: it's easy to get even coverage with the stuff, and it doesn't force you to rush assembly, you can let the coated gasket hang for days.
Jake650
XS650 Addict
Hey guys it was me that asked the question. Only reason I went PM route was thinking I would get a quicker response as DogBunny was holding the parts. Lesson learned...
256 motors (1970-73): 22 mm. 447 motors (1974 and forward): 20 mm. First run of XS1s had needle bearing wristpins; didn't work too well....
