broken and jammed piston rings

I'm starting to work on a 1980 Garelli Rally Sport I recenlty acquired. The engine is seized in a most horrible manner.

The piston rings have broken inside the cylinder and wrapped around the piston. What I mean is this: The rings are jammed BETWEEN the piston and cylinder and jamming out (like little horns) along the sides.

Is there ANY way to rescue either the cylinder or the piston (or both)? I do have a spare Garelli engine, but that one has no piston. So I also have no idea what size piston would fit.

But I'd like to rescue this other engine first, if at all possible. How do I go about doin this? Any ideas for this tought job?

Re: broken and jammed piston rings

You will probably just have to pound it out of there.

If the cylinder was worth thousands of dollars a machinist would cut a hole in the piston top and cut the piston into 2 pieces from its inside to let it come out with as little damage to the cylinder as possible.

You could still do that with a drill and hacksaw if you wanted to.

But it must have seized/broken on the fly.. and there is already damage.

So you might just lube it up and pound it out the "short side" and then plan on boring the cyl over if the damage is too bad.

Re: broken and jammed piston rings

This brings up something I have been meaning to ask here...

And that is... What are all our different motors... Bores and Strokes ?... my intention being to find out which original equipment piston is the biggest bore diameter so that some old cylinders can be salvaged by boring to a slightly larger piston from another manufacturer.

In other words... put a Tomos piston in a Suzuki?... (if possible)

I believe a lot of the aftermarket pistons are of inferior quality.

And many would be better off with another original equip piston ... if they would fit.

But we would need 3 different dimensions.

Bore dia

"Deck height" from the wrist pin to top of piston.

Wrist pin dia.

Then we would have to have ring locator pins that wouldn't let a ring pop out into another engines ports.

Everybody bring your old pistons to that BBQ... and mark them with the make, model and year ... and let somebody take them and measure and investigate the possibilities.

A piston database?... : )

Re: broken and jammed piston rings

oh, i'm not worried about the cylinder. my other engine has a fine cylinder and head. i was only hoping i could save the cylinder. but i already figured it was a bust.

but any idea on how to measure the cylinder diameter to find out what size piston i'll need? garelli made at least three sizes, so i can't just order a "standard". i assume it should be the same size as the one from the seized engine ... but one shouldn't make assumptions.

also, a piston database would be a fine idea. though i'm not even sure what kind of pistons i'm currently using ... let alone to make comparisons ... it'd be a painstaking long work.

Re: broken and jammed piston rings

gimmejimmie /

sounds like it's tryable Fred,

what about connecting rod travel and crank spin circum.? could be a Rubic's Piston puzzle, sounds like fun, ask your professor.

I once made a PVC bazooka that fired potatos with a hair spray fuelant, kinda like a piston in a cylinder.

let her rip fred!


I think people are going to party at the picnic, not compare pistons, but being a motorhead, I would bring ALL my spare parts. (sounds like a swapmeet in the making?) but I'm too far away.... partyhardy pedders!


Re: broken and jammed piston rings

gimmejimmie /

I just went to the bathroom and it came to me....

Deck height would be the determining factor, nevermind

another thinktank moment, or stinktank.

Re: broken and jammed piston rings

I'm not talking comparing AT the picnic... just to bring them and send them home with somebody... preferrably so I can measure them later... and it wouldn't be a long process at all.

I could measure and record one pistons specs in 5 minutes.

And the only thing a "doer" of this mod would have to do is trim the piston skirt if there was interference with the crank at the time he does it... no biggie.

The only difficult part about this is getting all the pistons to one person who could/would do it... cause a lot of people have prob thrown them out.

And the point here Miguel is... to not to toss your old cyl... even if it looks bad... because with a bigger bore option.. it is still useable.. even a possible high perf option.

And if you are considering a "bore kit" for yours... the guy who will do the boring should choose probably the piston for you... As far as measuring.. you either need a dial caliper or a set of telescoping guages and a micrometer...expensive precision tools.

Re: broken and jammed piston rings

Reeperette /

Tomos uses a 38.00mm diam, and has a 38.50 diam as an overbore.

A3 uses a 10mm pin, A5 uses 12mm pin.

Mopedjunkyard has good pictures thereof and prolly knows the measurements exact.

Imma usin the only Tomos Piston I got, sooo...


Re: broken and jammed piston rings

Reeperette /

Oh..duh me...If I can find it, I will bring the torched piston from the Suzuki...


Re: broken and jammed piston rings

hey, i can order a piston ... but i need to know how to measure the good cylinder i have for a piston. the good cylinder is a fine engine. it's just a matter of popping it on the bike and riding it. the bike is in great shape otherwise (just a few scrapes and flat tire). as far as we know, after a day of work it should be ready to just ride away .... once i have a piston for that cylinder.

should i just order the "standard" garelli piston? i'd like to be riding that garelli THIS week is the thing. unless my engine for the bianchi arrives before then. ;-) either way, i still want to ride the garelli and se what she can do.

and don't worry about throwing away parts. we never do that. even seized engines have good parts in them. we have a regular junkyard going on here. you should just see it to believe it.

Re: broken and jammed piston rings

I see what you are doing...

The only way to really know is to have it measured by an experienced bore guy with his precision measuring equipment... or just take a chance that it isn't worn too far (or already bored oversize) and that a standard bore piston won't already be too loose as soon as you put it in.

Re: broken and jammed piston rings

I know a decepticon who told me he has a set of calipers for measuring cylinders. He might volunteer his time and tools if we ask him nice.


Re: broken and jammed piston rings

Hi! If you like the `ped,buy another jug and piston,re-ring it, and `ped on.(After breaking it in for 300 mi. or so first)

Re: broken and jammed piston rings

Hi! Listen. While you've got it torn down, why don't you hone your cylinder lightly and install new rings.Could be those old rings won't be too good when you reinstall them.Just break it in for 300 mi. or so and you'll have some of that old power back again.I generally don't tear anything down without putting in some new parts,unless I'm hurting for time or money. BYE!

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