Modern Vespa

Hi all,
I have a spare 200cc cylinder/piston/rings set lying around and the cylinder is lightly scored from a cease. The piston looks fine save for a few very very light scratches by the exhaust port but I'd like to make it a working kit so that if needed, I can have it ready to install if/when the time comes.

I also picked up a honing bit really cheap at a Harbor Freight store sale this past weekend. This bit has the three arms that press outward on the cylinder wall and an adjustable collar with a spring to put more or less outward pressure on the stones.

This cylinder that I'd like to hone is at 3rd oversize (66.9) already. I remember when I got this kit together, I also got the 3rd oversize piston ring kit and a 3rd oversize piston. I recall the rings not needing to be filed down because the rig gap was at the minimum gap, so I left it as it was.

Questions:
A. Now that I am going to hone the cylinder wall to get past the scratches, do I need 3rd oversize or 4th oversize?

B. I'm guessing I can re-use the 3rd oversize piston I have, but do I need to get a 4th oversize piston if I get the 4th oversize rings?


Thanks in advance

If those scratches are deep the machinist might recommend skipping an oversize. After a violent seize I generally go up two sizes.

you are confusing honing and boring. Honing, that which is done with the tool you have from HF, is used to take light machine tool marks off the inside of the cylinder.

Boring is done with a boring tool, some very specialized, to take a lot of metal off the cylinder. After boring, you hone, after honing sometimes you use a paste to polish the cylinder even more.

Using that tool on anthing other that a decent drill press with consistent tool motion will ruin the cylinder.

If all you have are some light scratches, you might be able to hone them out.

Make sure the nut on the bottom is secure and don't pull the tool all the way out of the cylinder with it spinning.

Have a picture of the piston and cylinder?

Case 1, light vertical scratches in the cylinder:
If the scratches are light I just do a hone to make sure the crosshatching is good, not trying to remove the scratches. I'll also hit any shiny spots on the piston skirt with some 400 grit paper. New rings are a good idea but may not always be needed.

Case 2, Grooves in the cylinder or piston deep enough to catch a fingernail:
If the groove is large enough to catch your fingernail in then you are most likely looking at an overbore and new piston. I'll sometimes hit these with a hone and then recheck the grooves. Often in this case you will see wide sections of the bore that has vertical grooves (mostly on the exhaust side).

Case 3, Damage due to broken ring or circlip:
When a ring breaks and gets caught in the port it will tend to make a very deep groove. Many times it will take more than one oversize to clean this up.

Oh, this cease, when it happened was not violent at all...once I felt it start to stumble I grabbed for the clutch...pulled over and kicked it over and started right up...literally like that. Sad that I am getting used to the ceases

Yes..I have a drill press for this.
I'm under the impression that honing would smooth very small scratches that are on the cylinder wall.
Thanks for explaining.

Thanks for the info. I'm going to try and take a picture of it tonight and throw it up here.


PS: Love your fashion sense.

Let's go a little further.

Scratches are bad for a number of reasons. Deep scratches at the top of the cylinder prevent the ring from sealing and can ruin the cylinder as hot gases slip by. Light scratches and/or incorrect hone technique will leave a rough surface and ruin the rings.

tilting the tool and not using proper technique will cause more problems than you fix. Also, if something comes loose on the tool, which has happened to me once, you can kiss all your hard work goodbye.

Make sure the tool matches your cylinder radius. Also you want to figure out your start and stop landing area, usually at the bottom of the cylinder. So you want to invert the cylinder usually.

I've mostly honed small cylinders under CNC control to maintain a nice hatch. Make sure everything is clean and if you have an older cylinder, try it first or get some wide pipe to practice on. Remember the tool has to span the ports (if any) so the legs need to be long.

The HF tools are mostly for lawn mower and other low RPM 'who cares if it blows' projects but what the hell, the only way to learn is to try.

ps: make sure the cylinder is dialed-in to the spindle and mounted to the table. I use a somewhat expensive coaxial indicator. You can get a cheaper setup online for around $89.

Funny thing is they used to have boring and honing setups for older model T and later engines to enable people to do a "roadside rebore". The mounted to the top of the engine block while still in the car.

I Honed the cylinder on my P200 following a seize with the same exact tool from HArbor Frieght. I didn't go up a size or anything I just did it hoping that I would get my bike running again. I can report to you it worked. At least for a little bit. I think I put about 200-400 miles on it following the hone and used a new piston and rings as well. After the aforementioned 400 miles or so the rings broke in and the bike would start but not run well or at all worth a damn. It's being bored to a 2nd oversize right now. Skip the hone and do it the right way or you will have strong calves like I do from pushing the bike up hills trying to get it back to your house.

luckily I have not pushed mine very far at all..only once when I ran out of gas about 1/4 mile from home (.....and I have a fuel gauge and reserve light too!).


I am going to see tomorrow if the scratches are deep enough to catch a finger nail on it, then I'll decide, I guess.

I will be looking forward to having a spare cylinder though. when one craps out, swap and good to go!


...so sad. LOL

David Webster makes references in his tuning book to using a three-stone hone to go oversize. He says it would take all day. This was back when racers took any and all chances to win and didn't have a lot of money to spend.

Fortunatley for you it will be a door stop for a long time.

The chances of needing a spare because your original Italian barrel or piston crapped out is gonna be rare.

I have many door stops...every vehicle I own is 20+ years old.
I really need to start 'trimming the excess'....

I was going to say a month on a 3 stone.

It isn't practical as the cylinder would be ruined since there would be no way to keep a consistent diameter. The rings would flex a couple of million times as the diameter changed and break. Those stones are made for taking the boring tool marks off and that is about it.

So after reading this post carefully (on a PC and not on the phone while waiting for meetings at work, etc) I think the best option is to take it to the local guy that bored the cylinder I am currently running and ask his opinion.

If he can hone it, great... if it needs a re-bore then I'll cross that bridge when I come to it.


Dcunited4life, thanks for that info...that's exactly what I do not want to happen. I'm leaning toward a more professional means of cylinder treatment.

Thanks for all the info Cncjerry and all other contributors.

This is a very imformative topic, nice going guys.
Just wandering when machine shops bore over size on these cylinders are torque plates used?

Torque plates are mostly for multi cylinder boring applications.

Since this thread seems to be in the ballpark of what I'm working with, I thought I'd bump it. Already so much useful info.

I had a busted circlip gouge the space between the two intake ports. If overboring is a consideration, what are the recommended piston-bore clearances (range)? This will give me an idea whether or not I can bore it at all.

It's a 2-port Pinasco 177cc Cast iron cylinder
Pictures to follow

This is what's available:

http://www.scooterwest.com/item_details/PISTON-FOR-PINASCO-177CC-TWO-PORT-63mm--63-4mm--or-63-8mm/5561

Clearance should be .005 or a little loser any tighter you run the risk of a seize. Hate to say it but few shops can or will bore a two cycle jug and those that do still want to be paid, it costs about the same to just replace. Keep in mind if you buy new it's a kit with a jug and piston if bore you still need to buy a piston.

I've done some further research and yes, you are correct. It would be more costly and take longer. I just ordered a new kit on SIP. Will be here Tuesday. Cost me $288 delivered.

I have run clearance .002 for watercooled, .004 for aircooled - and I think .035 is possible. But that depends on the quality of the bore, piston, rings, etc... and also what you are going to do with it.

Tierney I think you're thinking four cycle and not two cycle. Maybe there's someone who knows better than I. $288 however isn't bad for a new set up.