Cylinder advice

[lam1962brettagg]

Hi all
looking to get a new/s/h cylinder for my s3 li150. (standard)
where the hell do I get one? looked everywhere. even fleabay which have dubious indian ones advertised for li150 but too cheap to be descent.
everything i've seen is for gp.
am I missing a trick here? if i cant get an li s3 what do i need to do to make a gp cylinder fit? thats if its possible?
has anyone else got this problem?
not that knowlegable if its not standard. sorry.
cheers for advice/help

[NorthernJordan]

GP 150 and Li 150 cylinders are interchangeable. So there will not be any issues in fitting the GP cylinder.
GP 150 cylinders will offer ever so slightly more performance than a LI cylinder so you may have to alter the jetting slightly.

I'm assuming your current engine has a cylinder on it? Is there any reason why you are looking to change for new?
Oversized pistons are easily available to make good an older cylinder.

Second hand cylinders should be easy to find if you are without a cylinder. Many will have been removed for tuning upgrades over the years and I would think a wanted add on here would find you one.

[lam1962brettagg]

Hi Thanks for reply
i was under the impression that gp cylinders were ported differently so had to be altered?
i'm after a new one because the i had a new piston and rebore. the engine would seize after six miles or so. (soft seize)
also gumming of the rings and an oil leak from the exhaust port joint.
after examination the partial seize was on the exhaust side of the piston adjascent to the oil leak.
i'm suspecting a hair line crack in the cylinder by the exhaust port. so to rule this out just wanted a new cylinder.
hope that makeds sense.
cheers

[lam1962brettagg]

hi again
tried once with a wantedd add and ended up with what i believe to be a second hand gp cylinder with knackered thread in one exhaust stud.

[NorthernJordan]

They are ported slightly differently (with slightly better performance).
However, the difference is fairly negligible but will needing jetting to suit.

There will be no issues pairing a GP cylinder with your current piston provided that the piston/bore clearance is measured.

Cast iron barrels are pretty robust and i'd be surprised if there is a hairline crack? (anything is possible though )

Consistently seizing would suggest to me:
Piston bore clearance too tight.
Jetting too lean
Timing out
Air leak

Plug colour will help determine what has been going on.
Most seizes are on exhaust side due to hot gases trying to escape.

[lam1962brettagg]

thanks for info. really helpful.
when you say air leak could that be from exhaust port where oil leak occurs?
(down pipe nut not tight enough?)

[nickw]

I'm with Jordan on this. A hairline crack is unlikely (but not impossible) Because you have indicated the seizures started after a rebore and a new piston it would suggest a tight bore. I'm no expert here but you need to measure the clearances with the rings and check the piston to bore clearance.
If you still need a barrel ebay has barrels occasionally for 150's advertised and they don't fetch a lot. Facebook may also have them on one of their lambretta parts sites.

[lam1962brettagg]

thanks for your input Nick.
cant see any cracks on the cylinder but find it odd that it only partial seizes at 6 miles or so.
no marks on the piston apart from small seize score on exhaust side. will check clearance again though. and have the cylinder honed anyway.

[NorthernJordan]

After 6 miles or so it's likely that the piston is only getting up to temperature and then expanding leading to a seize.
Like I say the exhaust port side is always hotter so you are likely to see the results of a soft seize in this area.

If you can't see any cracks then I think you might be over thinking it - easy to do when you are having issues with your own scooter....

Check bore clearance with piston(stickies book has good advice), rebuild and perform a leak down test (plenty of good threads on how to do one on here). Once you have done that report back with your findings and maybe supply a picture of your plug colour.

[HxPaul]

thanks for your input Nick.
cant see any cracks on the cylinder but find it odd that it only partial seizes at 6 miles or so.
no marks on the piston apart from small seize score on exhaust side. will check clearance again though. and have the cylinder honed anyway.

S.R. do a complete cylinder,piston and head kit for a GP 150.http://www.scooterrestorations.com/lamb ... -head-sil/

[lam1962brettagg]

Hi Paul
bought a cylinder and piston from said company in the past and found it was v poor quality so didnt fit it.

[lam1962brettagg]

After 6 miles or so it's likely that the piston is only getting up to temperature and then expanding leading to a seize.
Like I say the exhaust port side is always hotter so you are likely to see the results of a soft seize in this area.

If you can't see any cracks then I think you might be over thinking it - easy to do when you are having issues with your own scooter....

Check bore clearance with piston(stickies book has good advice), rebuild and perform a leak down test (plenty of good threads on how to do one on here). Once you have done that report back with your findings and maybe supply a picture of your plug colour.

Hi again
thanks for input. will recheck clearance but am a while off rebuild yet.
last time it ran the plug colour was ok. nice light brown colour and nice equal burn on top of piston.
maybe a while before i get it alltogether again though.
cheers

[hullygully]

"the i had a new piston and rebore. the engine would seize after six miles or so. (soft seize)"

how many miles had you done with the above rebore & new piston?

[gp200ts1]

I've got a 150 barrel you can have for the price of postage. i have a few which could be li, sx or gp. all 150 but would benefit from a rebore and a new piston fitting.

[lam1962brettagg]

"the i had a new piston and rebore. the engine would seize after six miles or so. (soft seize)"

how many miles had you done with the above rebore & new piston?

Hi
went out on it a number of times. probably 5 or 6 times. every time the same. all in all probably did about 30 or so miles.

[lam1962brettagg]

I've got a 150 barrel you can have for the price of postage. i have a few which could be li, sx or gp. all 150 but would benefit from a rebore and a new piston fitting.

hi thanks
if you can guarantee its Li s3 150 maybe with pics i'm interested.
will pay you though.
dont expect somethin for nothing.
cheers

[lam1962brettagg]

"the i had a new piston and rebore. the engine would seize after six miles or so. (soft seize)"

how many miles had you done with the above rebore & new piston?

Hi
went out on it a number of times. probably 5 or 6 times. every time the same. all in all probably did about 30 or so miles.

now fitting new casa crank bearings seals/ new casa exhaust.(sx type)
might seem a bit much but want to rule out any other possibilities. belt braces and a bit of string for good measure lol
cheers

[hullygully]

so, if you've only done 30 or so miles on a new rebore & new piston, presume you're only doin 30 miles/hr @ 25:1?

[lam1962brettagg]

so, if you've only done 30 or so miles on a new rebore & new piston, presume you're only doin 30 miles/hr @ 25:1?

yes thats right.
didnt open it up in top gear .
wanted to run it in properly.
forgot to mention that the drive side bearing (or casing nearby was too hot for my liking) so suspect possibility of dodgy korean drive bearing.