Case bore to cylinder sleeve issue on M8's?

[biggzed]

Not sure if Jim Robinson is a member here, but looks like he found a significant issue on the M8's. Documentation on his site.

Anyone else run across this situation?

http://headhoggersllc.com/m8-issue-update/

Zach

[rbabos]

Not sure if Jim Robinson is a member here, but looks like he found a significant issue on the M8's. Documentation on his site.

Anyone else run across this situation?

http://headhoggersllc.com/m8-issue-update/

Zach

Not quite sure I buy all of that. No spigot is supported to the point to prevent cracking. There must be some clearance for different exapansion/contraction rates. Even with a .005 clearance it could crack if there is some other issue in play. I have to wonder about stress risers in the spigot or the material itself. Several builds have the piston poking out of the bottom and rock. However seeing this, I'm even less warm and fuzzy about the M8.
Ron

[Geezer_Glider]

Uh the spigot on Harley cylinders has never been designed to be supported by the case. In fact if it gets snug , especially in one point or if the spigot is too thin you will have damage. Too long of a stroke with too short of a spigot is also a short life motor. Having not enough clearance between the rods and spigot, or as the roller bearings fail in the rods or mains can cause real quick destructive disassembly of the motor. (My guess for the pictured results)
Just saying (the sky ain't falling)
R Meyer

[wfolarry]

I agree it's a non issue. There has to be clearance for the cylinder to grow. Cases expand & contract. Too much clearance is better than too little.

[rbabos]

Uh the spigot on Harley cylinders has never been designed to be supported by the case. In fact if it gets snug , especially in one point or if the spigot is too thin you will have damage. Too long of a stroke with too short of a spigot is also a short life motor. Having not enough clearance between the rods and spigot, or as the roller bearings fail in the rods or mains can cause real quick destructive disassembly of the motor. (My guess for the pictured results)
Just saying (the sky ain't falling)
R Meyer

How any of those damn engines hang together and last as well as they do with the piston poking out of the bottom at BDC is still a mystery to me. Just plain wrong in so many ways , I tell ya.
Ron

[Don D]

He states:
"When doing a 114″-118″ ( base 107″ ) the cylinder sleeve is thinner, but still well within safe , where it goes in the case."

Well maybe not so safe

[rbabos]

He states:
"When doing a 114″-118″ ( base 107″ ) the cylinder sleeve is thinner, but still well within safe , where it goes in the case."

Well maybe not so safe

It also points to a substantial amount of piston rocking in order to crack the spigot, thick or thin at BDC.
Ron

[BigT]

I wonder if the cracked cylinder in the picture is a stock cylinder that was bored for their 118" piston. I'd personally have the SE 114" cylinders bored bigger knowing there's going to be a little extra meat left.

[biggzed]

I was confused by that statement as well. So is .160" an acceptable case to spigot tolerance?

Zach

He states:
"When doing a 114″-118″ ( base 107″ ) the cylinder sleeve is thinner, but still well within safe , where it goes in the case."

Well maybe not so safe

[Don D]

Yes but so is .030. I do not agree with his appraisal. If I was trying to fix this I would sleeve a stock cylinder (or look aftermarket if they are out yet) to increase the spigot thickness and not consider the case as a support of any sort. The case to spigot needs clearance or it will pinch the sleeve and seize the piston. There is expansion taking place hot.

[joe_lyons]

They can also crack if the bore is off center.  I know the earlier TC cylinders had this issue when going to 98".

[Don D]

The 4.060 TC cylinders are notorious for this. Some break even without an overbore.
The bottom line is however the case is not for support, the spigot needs to be strong enough to survive the turn around assuming the other parts of the assembly are good.

[Don D]

So what is the case bore diameter of an M8?

[choseneasy]

I have heard( but not personally seen) people claiming to run stock bore cylinders on 3 5/8 big bore cases on Evo motors. Basically a person using 3 5/8" inch cases with stock cylinders.
  As said above- more clearance is better than less- it makes me think this may have been done successfully??