Panhead cylinder replacement advice

[Headofpan]

Hi Everybody,

I hope you are all well and have had a nice year enjoying your bikes!

I am currently in the process of rebuilding a 52 Panhead.

The cylinders that were on the bike previously were ZEL (old repop) and they had been bored several times so I have opted to replace cylinders, pistons, rings, pins etc.

I purchased a "ready to run" cylinder & piston kit here in Europe from Zodiac. (I assume these might be the V-Twin kit rebranded) I opted for this package as I don't have a bore/hone here at home.

As this kit comes pre bored and honed I thought it would be best to check piston size and bore size.

My question is for you guys out there with experience is: what piston to bore clearance is generally accepted as optimal?

My OEM manual calls for between 0.001" and 0.002" and Clymer calls for between 0.0015" and 0.002", but from what I have read online some people go bigger than this.


My second question is that both of the new cylinders that have arrived appear to have a very faint scoring mark inside them. (Photo attached) This is very light however it can somewhat be felt when scratched with a nail. Do you think this will cause any issues? Any ideas what this would have come from?

Many thanks!

Tom

[image][/image]

[10Pin]

Since you ordered a package, you most likely have cast pistons. On bores under 4", with cast iron cylinders, I generally run 0.002" clearance. With forged pistons, I add an additional 0.0005". This matches guidance from KB and Wiseco, which are the two brands of pistons I most often use. If you go more snug than this, be sure to slowly and carefully warm the engine, even after the usual heat-cycling and break-in is completed. Aluminum pistons expand considerably faster than cast iron.

Regarding the scratching, it is tough to say from a photo, but that looks like tool drag to me... If it is, that would be a machining defect. Ideally you would work with the manufacturer and/or distributor that you purchased it from, and they would take care of it. In any case, if you can feel it with your finger nail, you do not want it in your brand new cylinders!

If some type of exchange isn't possible for some reason... Since you don't have direct access to the machine tools, you could "try" cleaning it up with a Brush Research or equivalent ball hone. Light pass (I said LIGHT!), clean, inspect, measure, repeat as needed. This is obviously not optimal, but it might get you on the road. If you can't get them to "clean up" without exceeding ~0.0025" clearance, only other option would be to source +0.010" pistons and have the cylinders re-bored / honed.

Just a BTW... Whenever I have to use V-Twin cylinders, I just automatically source +0.010" pistons, and give the brand new cylinders to my machine shop to fit accordingly. Even if they are supposedly "sized", I don't trust it.

[Headofpan]

Hi 10Pin,

Thanks very much for the detailed reply. Thats a great help.

I got in touch with the vendor and they have agreed to replace the entire lot. So thats good news.

When the new kit arrives I will check sizing. I am hoping that the piston to cylinder wall clearance is within spec on the new kit.

That is good information regarding the .010 over as well. I will keep that in mind next time I have to do one of these.

With regard to boring/honing, do people recommend torque plates on these old panheads?

My reason for asking is, Im sure a local shop could bore and hone the cylinders for me, but I can almost guarantee that they wont have torque plates for a 50s panhead where I live.

Thanks again,

Tom

[Mongrel505558]

You don't need torque plates for .010" over. When you get to around .060" then maybe.

[panheadrider1961]

Can you pull cotton ball over it and it pull lint off? If not gentle honing as has been suggested

[flat38]

My aftermarket UL cylinders had similar marks that could be felt with a fingernail. A few passes with a 320 ball hone smoothed them out and didn't cause any measurable difference in piston fit.

[RooDog]

In any case it's good to run a ball hone through most any cylinder after it's been "finish honed", Just a little bit will do ya'....
....RooDog....

My V-Tedd Cylinder.... As delivered before I thoroughly cleaned them with hot soapy water, and bore brushing all the holes....

DSC02020.JPG (150.94 KiB) Viewed 498 times

[10Pin]

Head of Pan - Sorry for delayed reply, I've been tied up for a few weeks.
Anyway, I prefer to ALWAYS use torque plates. However, as was stated, 0.010" on cast iron cylinders... You can probably get away without them.
My machinist is just super particular. (which I like...) We use torque plates on every bore, every time.

[kitabel]

The hone patter should be at angles (45, 60?) in both directions, not lines almost parallel to the deck surface.
If the hone is too fine, the rings will take longer to break in, but may last longer.
Chrome rings require a relatively coarse finish, cast iron much finer.

[Headofpan]

Hi everyone and thanks so much for the help and advice with this one.

As a follow up; the supplier exchanged the cylinders for me free of charge so I now have new cylinders and pistons.

The new kit they have supplied has a piston to wall clearance of 0.001” which according to the book needs extreme care during break in as to not seize it solid. For that reason I am going to get my local shop to bore/hone them to 0.0017” which should make my break in less nerve racking.

Thanks again,

Tom

[RooDog]

I just hope your new hone job, you are going to get, does not put you back to what that first pair of jugs was. I would not sweat .001" Clarence as long as I had good quality rings, and just a little care on your part.
You are not racing that bike are you?
....RooDog....

[Headofpan]

Not planning on racing at all! Going down the road without blowing up and without seizing is what I’m going for!

I’m using Hastings rings.

Do you think 0.0017” clearance is reasonable?

The machine shop would just be honing 0.0007” (+\- what the current bore size is)

Tom

[RooDog]

I find it very difficult to find someone to do what I want done, the way I want it done.
So the question is who do you trust, the machinist with his hone, or you with the throttle?
Hastings is a brand name, they make all sorts of rings including iron, chrome, and molly filled. ( BTW: there is no such thing as chrome molly rings), I prefer the molly filled rings, and each has it own hone finish spec, and break in procedure.
Again, it's up to you. Your money, your choice....
RD

[Headofpan]

Thanks Roodog.

The machine shop I’m using are engine rebuild specific. Although I haven’t used them before they do come well recommended.

I feel the same about finding people to do a job as asked…! Let’s hope that these guys can perform the job I want done!!

Will let you know how it goes…
Tom