lack of compression - rotax 123

[rockers]

hi all, have only been able to get my af1 125 going once and for 30secs to a min long then it stopped. checked everything else and seem fine. checked the compression using a compression tester and it read 25psi which is very very low, where do i start in finding out what causeing this ?
before i got the bike it had new piston and rings and 1st time it ran since it had a rebuild was when i got it. so may have not been assembled corectly any ideas ?

[Kickstart]

Hi

Surprised it started at all with 25psi compression.

My guess would be that someone has snapped the new rings when putting the top end on the engine.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

yes, but maybe was fine then started and put pressure on a seal or a gasket somewhere casuing it to loose compression

[Kickstart]

Hi

Unlikely. Only gasket that would really affect it like that is the head gasket, and that would probably mean that it would draw in a load of water which would (hopefully) be pretty obvious.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

probably will get killed for this but havnt got any water in the system atm as cleaning pipes etc, but wasnt intending on running it for any more that 30 secs without coolant,

my plan for tomorrow is to see if the head area bolts are torqued correctly failing that will take head off and check piston rings and barrel, is there anything to lookout for ?

Cheers

Rocky

[Kickstart]

Hi

A short run without water shouldn't really do any damage (I know someone who drag races a liquid cooled 2 squeak without any coolant in it).

The head gasket is a rubber O ring. I don't think the head bolt torque will be that critical (ie, long term might not be a good idea, but a small difference shouldn't kill it quickly). However possible that someone has put it together with the O ring out of position (it lives in a groove in the barrel).

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

ye, and what about the barrel and piston and rings, should i just be checking for broken ring ?

[Kickstart]

Hi

Without taking the barrel off you can't really check the ring. You can see if a snapped ring has damaged the barrel, and you can also see if the piston has smeared molten metal onto the barrel.

Think you would need to take the barrel off to check things properly.

Another thought. Someone could have bored the barrel out (ie, after fitting a liner) and then fitted a standard size piston. Depends on who rebuilt it.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

ok cheers, ive got full manuals for the engine so will know how to take it apart, but the gaskets if i take the barrel/head off will i need to replace them of should they go back on ok? they are new from the same time as piston and rings.

Thanks
Rocky

[Kickstart]

Hi

You shoud replace them, but bought on their own (Peter Knight will sell you the individual ones you need) they are cheap. Also the O rings for the head can normally be reused a few times. The only ones you need to disturb that cannot be reused are the power valve gasket and the base gasket.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

ok, found me problem.
took the head off noticed on the exhaust exit theres a small ding ither side of the bottem of the exit hole.
took the barrel off and the piston is messy on the front part of it one ring is pushed into the piston, so theres me problem
there is a little score above the exhaust exit about 20mm long and visable by eye and just feelable if you run your finger over it.

What now ? a rebore and new piston ?

Cheers

[Kickstart]

Hi

It is a plated barrel and cannot be rebored. You can either replace it, have it replated or have it bored out and a steel liner fitted.

However take the barrel along to someone to have a close check to see whether the damage is severe enough to warrent this. The "score" sounds like it can be ignored, but not sure about the small dings.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

if i put some pictures of the damage up on her tomorrow could you give me a rough idea?

have been looking on the net and i think that the barrel has a sleve in it, i will get pictures tomorrow.

Cheers

[Kickstart]

Hi

Can have a glance, but without seeing it in real life not really going to be that much use.

If it has a liner fitted then you can rebore it, just you need to know what size it is already bored to and get an oversize piston.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

oh ok, was looking on a website pjme and they do rebores to match a piston, so could get them to rebore and get a piston etc from them

[Kickstart]

Hi

PJ can supply o/s pistons.

Unless you have to I would personally prefer to stick with a plated bore.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

yes, will get a pic up tomorrow see if its been sleeved already. is there a disadvantage boring out ?

[Kickstart]

Hi

Not really in boring it out. Just that personally I am not keen in the idea of using a slieve in the first place.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

ok just got off my fat arse and got some pictures, https://img682.imageshack.us/gal.php?g=06122009119.jpg

Rocky

[Kickstart]

Hi

Think you are right it has a liner in it. That score is fairly deep, and the 2 chunks missing are not good. With luck it can be rebored, but possible that you might need to go 2 sizes over.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[rockers]

ok, wasnt sure as no idea what the barrel is ment to look like anyhow.

price wise looks like 25 quid for rebore and around 50 for piston rings and gaskets.
jw what caused it now as it was brand spanking new piston and rings when the chap before put them in wrong or had broke a ring putting it in.

Would you say i should run anything through the bottem half of the engine incase there is any debre at all there? water a no no dont want to use meths or petrol as willl take all the greese out of the bearings.

[Kickstart]

Hi

Could be that they snapped a ring putting it together, or possibly the ports needed to be finished off after it was bored.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing