Lis 125 starting issues

[Kristof Lammy pie]

Would you say this piston has suffered a partial seizure?

It's heavily marked with carbon and burn marks,

There is a light score on the piston directly underneath it.

[HxPaul]

If the shims dont appear worn i would use them again.As for the piston rings,if you insert them into the cylinder and measure the gap.The gap should be from 0.16mm to 0.6mm.

[HxPaul]

have a look at the top of the piston Chris It should be marked if its oversized .
If the bore is ok and the piston is not scored I would be tempted to hone the cylinder very lightly with some 250 grade wet n dry to remove the glaze and fit new standard rings to the piston and put it back together.
Its a pity you didn't test the compression before you removed the head because that would have told you something about the state of the engine components

If there is no score marks in the cylinder,I'd do as jonnyXS says and clean the cylinder and piston and check the ring gaps and rebuild.

[Kristof Lammy pie]

Ok cheers


Thanks for all the advice fellas. Really appreciate it.

Kris

[johnnyXS]

its difficult to see what has happened to the top of the piston from the image but I would suspect it is the result of detonation. At some point in the past the engine has run lean and hot and with the wrong timing perhaps .
I would just dress it off as well you can so that carbon doesn't accumulate. The burn mark on the piston is very typical and looks like the underside as it is fitted. it will wear , get hotter and burn more than the sides and top of the piston due to gravity Its not due to seizing and not a problem

[Kristof Lammy pie]

Cheers Johnny first class info again.

I thought the detonation would be on the spark.


Final question before I actually I do something for myself.

I bought a 42mm Ancillotti Scootopia exhaust for my TV175 and was impressed with the fitting.



Would this work ok on a small bore 125? If not what's the best exhaust system for it?
Ta
Kris

[johnnyXS]

thank you Kris . Unfortunately I have no experience of exhausts I'm afraid. But I know a man who does

Mark of MB Developments has written lots about all his research into design of performance clubman exhausts and I reckon his has got to be up there with the best of them judging by the amount of testing he did .
http://www.lambrettaspares.com/info/mb-*-tech-articles/engine-tech-*-mb-clubman-x+38.html
http://www.lambrettaspares.com/info/scooters-*-lambretta-/new-product-*-clubman+210.html

[coaster]

I've only just noticed this thread and read it from start to finish. Whilst there have been some very relevant suggestions, it seems daft to me to have progressed so far without checking the points and setting the timing. Especially all the buggering about adjusting the carb. If you now find a problem with the ignition the carb will have to be adjusted all over again anyway.

Before splashing out on a new exhaust, try slackening off the manifold nuts, all nuts should be left slack until the whole exhaust is fitted. Only when everything is snuggly in position should the nuts be tightened. Also, as Storkfoot said earlier, the exhaust flange can be easily dressed with a file, there is probably not much wrong with your old one other than that the flange has bent down at the ends (they all do this over time).

[Kristof Lammy pie]

I will get a gasket set and rings and get the barrel and head on and go from there.

The original u bend was knackered. I will check the exhaust again but to me it look miles off.

Once I've sorted that and I've got an exhaust that fits I will see how it runs.

[Kristof Lammy pie]

Measured the rings in the barrel and the gap is 0.6. I take it that's just acceptable?

[johnnyXS]

according to stickys manual the maximum permissible gap is 0.55m for 125 and 0.6mm for 150 so they are useable but on the limit . It would suggest that the engine wasn't rebuilt a few hundred Km ago
I would put some new rings in regardless but make sure you really clean the ring grooves thoroughly and with new rings you'll definitely need to take the glaze of the bore with some very fine wetndry or better still buy a cheap honeing tool like this one .http://www.ebay.co.uk/itm/19mm-62mm-Car-Engine-Brake-Cylinder-Hone-Flex-Shaft-Bore-Honing-Tool-New-/191393445002?hash=item2c8ff0348a:g:ywQAAOSwQPlV-AEY
Bung it back together and run it so that you can test everything like the gearbox, brakes etc and then you'll be in a better position to make an assessment as to how much work you want to do on the scoot .

[Kristof Lammy pie]

I think in going to have to get a piston too.

There is a flat on the side and I can get a 0.05 feeler gauge in.

[johnnyXS]

mmm that sure doesn't sound like an engine that has supposedly been rebuilt does it.

Now you are defintely going to be better off by far buying a complete cylinder piston and ring set . that way everything will be matched and fit well and you won't have any expensive Engineering costs.
I saw a 150cc kit the other day for about 80 quid. here we go http://www.ebay.co.uk/itm/Lambretta-Li150-Cylinder-Kit-Barrel-Piston-and-Head-SX-GP-/281918325374?hash=item41a3a4427e:g:XZkAAOSwksVTzn0h

Phone them and check it is the right one for your model as I am not that au fait with the 125 series .

[Kristof Lammy pie]

It's was probably a rebuilt motor using all the old parts! Lol.


I might take the motor out and do check it all I think. If he has skimped with the piston and head everything else could be failing too.

[johnnyXS]

now you're talking
See what happens when you just prod that little bit of rust !.....the whole World falls in on your head

[Kristof Lammy pie]

Exactly that!

[Kristof Lammy pie]

Slight change of plan due to my gp150 seizing.

I'm going to buy a new piston and rings and exhaust and put this back together and get it registered.

Then I can sort out the gp150 seizure.

Going to order the bits at the weekend hopefully I can get started on it next week.

[johnnyXS]

excellent plan Kris ! its easy to get overwhelmed sometimes when there are so many jobs vying for attention.
You've motivated me to get my shed sorted yesterday so I'm going to start rebuilding my spare engine this weekend too. See .....its contagious
Hope you'll keep us informed of progress....a couple of pics ouldn't go amiss

[Kristof Lammy pie]

Thanks Johnny


I will keep both threads updated with pics and probably questions.


Long term plan for me is to get a spare motor to practise on.


What lambretta do you have Johnny?

[johnnyXS]

I just have a 64 LiS150 special . I was lucky I bought mine just before prices started to go crazy.
I have been collecting parts to build a second scoot but prices for frames are just too rich for me . its more economical to buy a complete scoot really than try to build one from individual bitsso I shall probably have to look out for another complete LiS150 special or a TV175

I also have a yamaha XS650 twin from 1979 which I love riding and fettling equally. Back in the late 60's I wanted to be a rocker with a motorbike but all my mates were Mods so I got a scooter instead but I've always been torn between the two . Now i'm retired I had to have one of each .
This June Haynes Motor Museum Sprarkford are running a 2x day 60's Mods & rockers weekend. I'm going as a Mod on the Sat and as a Rocker on my bike on Sunday ....... happy days