Cylinder dilemma...

[Kuda]

So after thrashing for three straight days to get the pan back together (basically a frame up rebuild started last Dec), I finally got it together and after 4 kicks it fired up to a nice high idle. Glorious! For about 2 minutes, then I heard the tell-tale crack of an exhaust flame. Thought it was a head gasket, which would've surprised me, but no, it was a 1/8" hole in the rear cylinder. Victem of the dreaded "core-shift" mentioned here. It's a Zel cylinder, only .40 over, so it should've been fine, but after pulling it back apart the cylinder is paper thin in that spot. Now the question: my first choice for a replacement would be good used OEM cylinder that I can match to about the same size (like .030 to .050), but they're rare as hen's teeth apparently. So now I've got to choose: either a new repop, (which frankly make me nervous quality-wise) or a .070-.080 OEM cylinder. I've heard that it doesn't make a difference having different sizes, but I'd like a second opinion on that. The easiest, cheapest solution is buy a new repop with a matched piston (double checking the sizing, of course) and then weigh it and match the weight to the old piston (to avoid changing the balance). OR I could get the over-bored OEM and a new piston and repeat the above. What're the thoughts on those options?

-Kuda
'49 panchop

[Cotten]

Kuda!

Balancing a v-twin only considers the total reciprocating mass. Your pistons need not match each other, as it is not figured in the equation at all.
After all, the tops of the rods cannot be made equal.

After dropping a head off a valve early one summer, I ran for the rest of the season with .050" in the rear, and .070" in the front with absolutely no impact upon vibrations or even plug burn.
Only when I tore it down that winter did I find that the rear was standard compression, and I had installed a low in the front.

V-twins are very forgiving.

As I mentioned many times previously, I prefer an overbored OEM to aftermarket, however the uses of torqueplates when fitting is manditory.
It may have even saved the ZEL, if the coreshift had been detected in time.


....Cotten

[RUBONE]

True Cotten,
But by matching the weight of the new piston to the old, not to the other cylinder which I assume was being left alone, he would not change the overall mass!
Robbie

[Hauula Pan]

Just so info. to chew on. I am currently running .070 on both front & rear. As far as I'm concerned that's max. I wouldn't go .080 its just getting too thin. I would be very concerned with any after market cylinders. I've just had way too much poor quality with the after market arena. Running mis-matched holes shouldn't be too much of an issue unless they are like way way different, say stock or .010 and .070, then I'd be concerned about heat and plug fouling. Given a choice I'd try to find some stock jugs and bore them before going the after market route. But that's just me & my experiences. I'm sure there are others who've run after market jugs etc. without any problems. I just don't trust em.

[NightShift]

I've done them .100" over.

Just gotta know the tricks.
Ifn you don't, boom.

Really respectful ,

NightShift.

[LittleAl]

stupid question: can't OEM jugs be relined? I thought they had a cast iron sleeve that could be replaced.

[RUBONE]

Al,
Factory cylinders are cast as one piece, no sleeve. However, any cylinder can be sleeved but most people only do that as a last resort due to strength issues.
Robbie

[Cotten]

Dixie imports fine quality pistons to .100" oversize.
Please inspect any large overbore for wall thickness, and as I must emphatically restate: the use of torqueplates when fitting is manditory.

I have written previously about a 61" Knuck that I produced at .155" overbore.
After nearly a decade, the most recent owner (who shows it no mercy) has brought it to his local service shop for a fresh top-end, who contacted me.

Only because they have no torqueplates, they are compelled to replace the cylinders. I look forward to inspecting the cylinders someday, as testbeds of such documentable history are quite rare.
And I would love to have them for my own use, as at .165" over they will achieve a square motor.

...Cotten
PS: A sleeved cylinder should be torque-plated even at standard bore.
Sleeved cylinders suffer more from heat retention than from the weakening of the casting.

[Kuda]

Thanks for all the help guys, I really appreciate it. Still unable to find a useable OEM cylinder (well, I did find one that was .070, cracked fins (3), and needed to be surfaced top and bottom for $140, but I passed on it ). But I did find an old aftermarket cylinder cheap that hopefully will be here tonight. My thinking is that if it's used, at least it's seasoned and any obvious problems will have shown themselves. Without access to a magnaflux set up, I'm kinda at the mercy of the machinist. Got an appointment tomorrow morning with a very good machine shop to have it bored to .030 and finish honed to .040 (only local with torque plates for a pan) so I can use my old (with 2 minutes running time on 'em) pistons. I'm going to keep my eye out for a set of OEMs for the next go around, I guess I'm just putting too damn many miles on this thing not to have spares. Hoping to get the pan back up Saturday and get some break in miles on it, leaving in less than 3 weeks for another trip: DC to Houston, Texas to New Orleans to PA, then upstate NY for the Rendezvous, then back to MD. 'Bout 5k miles in 9 days. Won't be my longest trip, but it'll be the first one I've done that's not solo. Sure hope that evo and twinky can keep up...

-Kuda
'49 panchop

[preacher]

why cant you just weld it up and grind it down?

[NightShift]

I'd a passed on that OEM cylinder too.

Scrap ain't never been THAT high.

But if it was an overhead oiler, they go for that much. Worth fixing because repops will never be right.

NightShift

[Kuda]

why cant you just weld it up and grind it down?

I thought of that, but didn't think it was a safe option. I've since been told that it might work. I'm keeping the cylinder to do just that and keep it as a spare. Still trying to score some decent OEM cylinders for back ups. Oh, and thanks to all again, she's back up and running as of late Saturday. Still getting used to the Linkert and "dead" (unsprung) throttle, but on my short warm up run everything seemed to be OK. Noisy as hell, but it IS a pan.

-Kuda
'49 panchop (alive and kicking...)

[LittleAl]

Mule has a pair posted in the for sale section

[Kuda]

Mule has a pair posted in the for sale section

Thanks, I just bought 'em...

-Kuda