9 second bagger?
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From: poway
Without the rod angle, there wouldn't be any side thrust..
Pin offsets are still popular.. Wiseco and KB still do it.. CP and JE don't IIRC.. I remember Ron Dickey saying he used pistons without offsets because he had trouble getting them machined right. I would imagine the 107 m8 pistons would have to be a little shorter than 103 TC pistons as IIRC the rod lengths are the same and a 107 m8 is basically the same as a 107 TC..
If you want to see a short piston look at the ones Honda uses in their 250 cc dirt bikes like the CRF250f.. Kinda wonder why they don't turn sideways in the bore.
I'm not sure the 4.6 bore hangs out of the cylinder that much except for in the area where the 2 cylinders spigots are cut but I've really not messed with big bores in M8s. Don't know case deck heights, cylinder lengths, spigot lengths, rod lengths or piston CHs on them.
Pin offsets are still popular.. Wiseco and KB still do it.. CP and JE don't IIRC.. I remember Ron Dickey saying he used pistons without offsets because he had trouble getting them machined right. I would imagine the 107 m8 pistons would have to be a little shorter than 103 TC pistons as IIRC the rod lengths are the same and a 107 m8 is basically the same as a 107 TC..
If you want to see a short piston look at the ones Honda uses in their 250 cc dirt bikes like the CRF250f.. Kinda wonder why they don't turn sideways in the bore.
I'm not sure the 4.6 bore hangs out of the cylinder that much except for in the area where the 2 cylinders spigots are cut but I've really not messed with big bores in M8s. Don't know case deck heights, cylinder lengths, spigot lengths, rod lengths or piston CHs on them.
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From: Dayton OH
Steve sorry I have been offline. Max Headflow already answered your questions better than I could have. I might add if you have worked with big bore M8s the shorter stroke will as you know pull a little less out of the bore than you may be used to seeing with the 4.5 stroke. Always good to read yours and Max's commentary on builds parts testing etc. Its also going to be interesting to see George's challenges commentary and results good and bad with Blue 5-0.
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Steve sorry I have been offline. Max Headflow already answered your questions better than I could have. I might add if you have worked with big bore M8s the shorter stroke will as you know pull a little less out of the bore than you may be used to seeing with the 4.5 stroke. Always good to read yours and Max's commentary on builds parts testing etc. Its also going to be interesting to see George's challenges commentary and results good and bad with Blue 5-0.
Now as you stated running a longer stroke makes it even worse. The factory 4.5" stroke uses the same rod length and the piston pin is moved in the piston so it only comes down 0.031" more than the 107 does, but the S&S 4.625" stroke uses shorter rods so the rod angle increases and the pistons come out and additional 0.062" past the HD 4.5" stroke.
For a race engine that your going to rebuild after each and every race you can get away with it, but it's by no means, a good thing to do, if say you want 5,000 - 10,000 miles of service life. That said it will be fun to see how well it turns out.
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From: Dayton OH
Thanks Steve that is good info. As Max referenced I think Moonshine's jugs that George is running has longer spigots than you referenced except where they have been cut out for clearance. For whatever support that is worth. For clarity it is a 4.600 bore 4.375 stroke.
Well it is an experimental or race engine. George has said on TTT that it will never be a kit or for street use.
Do you think 4.500 bore 4.375 stroke can make for a reasonable life street engine? Moonshine seems to be doing it with their Jugs and I haven't heard of problems with it. That is only to say I haven't heard of any plus their isn't that many roaming the streets and or for that long yet.
Well it is an experimental or race engine. George has said on TTT that it will never be a kit or for street use.
Do you think 4.500 bore 4.375 stroke can make for a reasonable life street engine? Moonshine seems to be doing it with their Jugs and I haven't heard of problems with it. That is only to say I haven't heard of any plus their isn't that many roaming the streets and or for that long yet.
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Thanks Steve that is good info. As Max referenced I think Moonshine's jugs that George is running has longer spigots than you referenced except where they have been cut out for clearance. For whatever support that is worth. For clarity it is a 4.600 bore 4.375 stroke.
Well it is an experimental or race engine. George has said on TTT that it will never be a kit or for street use.
Do you think 4.500 bore 4.375 stroke can make for a reasonable life street engine? Moonshine seems to be doing it with their Jugs and I haven't heard of problems with it. That is only to say I haven't heard of any plus their isn't that many roaming the streets and or for that long yet.
Well it is an experimental or race engine. George has said on TTT that it will never be a kit or for street use.
Do you think 4.500 bore 4.375 stroke can make for a reasonable life street engine? Moonshine seems to be doing it with their Jugs and I haven't heard of problems with it. That is only to say I haven't heard of any plus their isn't that many roaming the streets and or for that long yet.
NO the 4.5" bore M8's are not holding up well on the street. It does not matter what the stroke, as the issue is the limited room in the case. When you step bore the case to clear the case alignment dowels that sets the lower limit for support to the piston. Without the piston support and the bad rod angles in the M8 your just asking for trouble. It get even worse with the S&S 4.625" stroker crankshaft as they shorten the rods to allow the stock pistons to be used, this means the pistons come even further out the bottom with little to no support. The 4.375" bore is as far as I can tell anyone to go for a Street ridden bike that you want to last for 50,000 miles of use.
As for using a longer sleeve it's no possible unless they address the case alignment dowels and to date I have not seen anyone doing it.
Max
The Honda doesn't have a 4+ inch stroke or a 4+ inch bore either so it like comparing apples to raisins.
Last edited by Steve Cole; Oct 2, 2022 at 01:44 PM.
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From: poway
[QUOTE=Steve Cole;20856334
Max
The Honda doesn't have a 4+ inch stroke or a 4+ inch bore either so it like comparing apples to raisins.[/QUOTE]
But the crf has a shorter rod to stroke ratio than HD 1.43 vs 1.75. Side thrust on the crf is higher when scaled..
Max
The Honda doesn't have a 4+ inch stroke or a 4+ inch bore either so it like comparing apples to raisins.[/QUOTE]
But the crf has a shorter rod to stroke ratio than HD 1.43 vs 1.75. Side thrust on the crf is higher when scaled..
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On a small bore short stroke with much lighter components, that 's not so bad. The mass of the HD is a much bigger deal when you put it all together
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