I have a 1999 270 contact Gasgas that hasn’t started for a good while. I’ve removed the head and the piston is approx 2 inches below flush with the top of the cylinder with a bit of rust (cleaned off fairly well) at one side. The cylinder doesn’t feel scored, just a few marks possibly from me rubbing a cloth around in there so it seems not too bad. I don’t want to go putting my weight through the kick start but having put a bit of pressure on it, and not getting much movement, I’m starting to wonder if the piston rings have rusted or dislodged and jammed in the exit up front where the manifold/exhaust bolts on. (clueless with bikes/engines so be gentle!)

I have ordered up cylinder head o-rings, a pair of piston rings (can return them if the piston isn’t the same) along with some other bits and bobs like fluids. I planned to drain it, top it up, fuel it and try and start it but I worry that if it’s seized, I might damage the gearbox trying to put my weight through it. The next step I think would be a good move would be to remove the exhaust and have a look in the front of the cylinder to see if anything looks odd. I also thought about laying it over and removing the clutch cover to see how it looks in there (bit of water in it laying about for a number of years worries me) but then I thought that I might be going a bit too far by doing the clutch cover as it’s still seized.

Am I on the right track here or is there something I should do or try before launching all my weight into something and causing more damage?

Help would be superb!

Thanks

Martin

Boiling hot oil is the usual cure for a well seized engine, but probably a good knock to the piston with a rubber mallet/block of wood will suffice!

Rather than use the kickstart, put it in top gear and rock the bike back and forth.

Now that you’ve got the head off squirt some penetrating oil down the bore, put a rag in the exhaust port if it is uncovered by the piston.
The most important thing is to not try and start it until you know that the piston is moving freely in the bore.
If it is liquid cooled drain it an flush through with distilled water before filling with fresh coolant. Check the gearbox oil for moisture as it is a good indication of a failed crank seal.. That should keep you busy for a while but do not attempt to start it yet.

built and run more trials bikes than i can count.. plus gas ( not wd 40) fill the top of the piston leave a couple of days and try rocking in gear.. then if not diesel is your friend pour on top of the piston and let it marinate for a couple of day then wipe it out and then hot oil is your next ingredient pour on top of piston and rock it back ward and forward in gear.. repeat if necessary half a dozen times till either its free or you know its completely solid.. if your sure its solid either a lump of wood hammered on the top of the piston or lift the barral.

once you get it moving flush out the engine with petroil and put it back together.. then sell it.. it is a gasgas after all.

then sell it.. it is a gasgas after all.

😆

I’m not familiar with the exact engine you’re talking about so bear with me. It sounds like the rings are siezed into the bore (as you’ve already found out) It’s no biggy but be careful as like a stuck seat post it’s possible to do a lot more damage if you’re in a rush to get results.

First thing I’d do is get some thin oil like diesel down the bore & let it sit. In itself this probably wont do a great deal but will provide a little lubrication once the siezed parts start to shift. I’d give this several days and numerous applications to find its way in.

I’ve found through experience that applying direct force to the piston crown if the best way of initiating movement. Using the kick start or rocking the bike incurs the disadvantage of a large increase in gear ratio.

You need to ensure the piston isn’t at BDC before you attempt to drive it down the bore. There’s no reason for the rings to have moved & caught in any of the ports if the engine was running before. They’re pegged into the piston & can’t rotate.

Fabricate yourself a drift out of softwood & with the aid of a lump hammer give the piston crown a few good hits with the drift. Mark the bore with a Sharpie to monitor your progress. If frame clearance is tight you may have to remove the engine.

A results depend largely on how badly rusted the rings & the bore are. (Is it a Nikasil bore ?) If the rings are simply (lightly) rusted to the bore then they probably wont put up much of a fight. It the bore has rusted round the piston the compressional forces on the piston can be huge & make it V difficult to remove without damage.

Once you get the piston free from the cylinder everything has to then be scrutinised minutely. The bore will probably have circumferential lines where the rings were stuck. These need to be removed completely. The piston……I’d ditch this along with the rings, circlips & small end bearing if you’ve had to use much more than minimal force. The ring lands can be damaged during the removal process.

Good luck.

D.

tbh Once you’ve freed it off take off the barrel to check and change the piston rings anyway, it is a 2-stroke.

Great, thanks folks. I’ve had a puddle soaking on the top of the piston for a week and have ordered up a clutch cover gasket so I might also pop that off and have a look too. The cylinder doesn’t look too bad and I reckon it might be O.K.

I’ll report back tonight after a few attempts.

Thanks.

“Fabricate yourself a drift out of softwood & with the aid of a lump hammer give the piston crown a few good hits with the drift.”

From bitter experience: make sure that the ‘drift’ is the full diameter of the bore and bears on the edge of the piston only, or you may find it’s easy to punch a hole in the piston crown.

(Give it a couple of days soaking in diesel first, though).

Unless you have to *really* welly it, I reckon it’ll be as right as rain.

Just spoken to a chap that was going to have a look at it for me. He is the guy to go to for all trials stuff in the area apparently. I asked him what it could cost if it was seized. He said it could possibly go to around £300 but if it’s been laying around with water and seized further down it could go up to 650+

I’m going to have a fettle right now. A gentle fettle. I’m not planning on thumping it just yet!

I’ve dropped it off with a guy that deals in trials bikes and he removed the cylinder and ran through a number of things up with it and the prices for repair. I can’t remember everything but piston kit and conrod were mentioned. At least £300 labour plus extra for some pressing on of the rod/bearing? Approx 500 parts.

I’ve never removed an engine on a bike before and I cringe at the thought of the parts springing out on me like a road sti unit! I’m wondering if I should get the engine out,split it and try and learn a bit about it all.

The other side of me really can’t be arzed as I fix bikes throughout the day (and would rather ride them after work, not continue faffing with them) and although some folk like these ‘hobbies’ I’m wondering if I’d be opening a can of worms by spending time, then more money, only to not have fixed it very well by missing out crucial stuff. Folk tell me 2 strokes are a piece of pi*” but it’s not going to be a piece of P for someone that’s got no clue of engines. I could easily miss stuff out. It reminds me of folk that try and fix their bicycles but make a dogs ear of everything as they are too confident for their own good. If I delve in here, things could go this way and I’m having thoughts of just getting something that’s actually running and usable.

Anyone want to buy a bike? :O)

Strikes me that you should cut your losses. Unless its damn near perfect you could get another for not a lot more and have your old one for bits or a project when you do it yourself.
Plenty of old trials bikes out there.

Yeah, it’s either strip it and see what goes on and learn a bit. Or put it back together and sell it for spares/repair. Would like to see for myself what has gone wrong though! I’m wondering if it’s really 480 quids worth of parts damaged due to rust. Surely not! Or am I in for a big shock?