RXS engine failure, no compression, help with diagnosis ?

[Dan79]

The engine of my RXS100 died recently - my fault I suspect, was revving it at too great a speed for too long. End result is, engine now has no compression, so prime suspect would seem to be that the piston has been holed or has melted.
However i have not dismantled the engine and no qualified mechanic has had a look. Question therefore is, in order to diagnose the fault with any certainty, what should I look for on dismantling? How would I determine the need for a cylinder to be rebored, or bearings to be replaced? Are special instruments required to gauge these thing?
My level of mechanical competence is pretty basic; I'm happy with working on disc and drum brakes, change tubed tyres, change chains and sprockets, i.e. spanner monkey jobs. Is working on an engine beyond someone with my level of experience?
The way I see it, the engine is probably a goner, but as someone who doesn't fully know what they are doing, am I likely to cause further damage by dismantling it?
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Previous bikes - 1984 Honda VF500 (FII) Interceptor and 1990 Yamaha RXS100
Current bikes - 1984 Honda VF500 (V30) Magna

[Taught2BCauti...]

There's not much work involved to get the cylinder head and barrel off - and you should be able to see what the problem is by then.

There are all sorts of dials and gauges that engineers use, but well outside the scope of the DIY mechanic.

A visual inspection of the head, piston and cylinder bore should reveal anything obviously wrong - then you will need to work out whether it is more cost effective to repair or replace, depending on what's gone.

If in doubt, take plenty of pictures (a mobile phone's camera will do) take written notes, and keep all the nuts and bolts in labelled containers (yoghurt pots are good for this) which will help if the engine will be in bits for a few days whilst you get it sorted.

Good luck.
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Honda Varadero XL125(V8)
www.TheFutureIsHere.eu

[Dan79]

[bikenut]

hi dude,

spanner monkey jobs eh......

anywho, check for play ( up and down ) and roughness of main bearings by removing plugs and killing ign., hold flywheel and try for any up and down movement.

rumble or sticky bearings with play up and down?? some in and out movement.........

play in big end, with piston half way down on firing stroke, any play tween crank and piston ( some flywheel movement but no piston movement ) may be little end also.

get manual........

remove head and see what you will see.....some pics and feedback for the site.

[Teflon-Mike]

Its an air cooled two stroke. It has three moving parts in the business end of the engine; a crank, a con-rod and a piston!
THAT IS IT!
The cylinder head is nothing more than a finned metal plate with a hole in it for the spark plug, held on with , I think just four nuts on the RSX....
Take that off you can see the piston, & with the cranc wound round to bottom dead centre, most of the bore, for any score marks.
Two nuts loose the exhaust flange, and I think just one more the silencer so that can be lifted out the way.
Carbuirettor is on a rubber flange held on with two jubilee clips between the reed-block and air-box. Loose them, and you can pull the carb out the way and simply slide the cylinder off the piston.
Piston is attached to teh con-rod with a pin secured by two clips. Pull those you can slide out pin, and remove the piston from the con-rod.
'Waggling' the conrod on the crank will give you an idea if the biog end has 'gone'
rolling the crank some idea of the state of the mains.
And you will be able to see into the crank-case for any debris from a ring or piston fail.
If you are lucky, probably needs no more than a new pistoin and rebore... you have at this point those two parts in your hand. One to take to M/C shop to get bored, othet to chuck away/ keep as a suvineer.
Then you can put new piston & rings back on, probably with a new small end bearing. Slide barel back over the top, clamp head down, (all with new gaskets of course), refit exhaust and carb, squib a little two-stroke oil theough teh spark plug hole & work the engine orver to get all nicely lubricated before first start...
Then give it a prod with the spark plug in.....
There is NOTHING scary in the air-cooled two stroke; it has no valves to seat or lap, or cam-shaft to time in, NOTHING...

BUT... you wont see for yourself until you start getting busy with the spanners!

As said, if you can take drum brake apart and put it back together so it works.... you can do one of these!

Get cracking, take pics and if you are unsure, post pic & ask opinion.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'