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Last year I removed the cylinder, head and piston etc from my standard S3 Li 150 (fitted new, but about 700 miles / 6 months of normal use, no issues, ran well ) and replaced it with a GT186 - all good....goes like a train couldn't be happier...........

And here's the problem.....

I recently bought a 1970 Italian DL125. The engine came without top end.. so I fitted the above surplus components from my LI + new 22m Scootopia carb, 42mm Clubman. Synthetic oil @3%. its also had new 12V electrics

Consistently the DL starts first kick, runs nicely for about 30 seconds, then a loud banging from the top end can be heard, followed by a seizure.

After a few minutes, the scoot can be started again (Still kicks first time).

I stripped the top end, there is no scoring or marks in the barrel or on the piston. Put it all back together - same result

Any ideas what to check next?

Also any theory as to why the perfectly running top end removed from the LI does this on the DL. I naively thought bolt it on and it would just simply work.

Did you check the squish when you fitted the top end? Just wondering if it's the piston contacting the head as it expands with heat? must say it is extremely unlikely that it is nipping up (virtually unheard of on tickover), it would need to have a seriously tight bore clearance for that to happen and yours has been good for 700 miles so can't be the issue.

Have you checked for anything catching on the flywheel/stator?

Hi Coaster - thank you for the quick reply

I have not checked the squish. ( I do not have a micrometre - I do need to get one....) but I did put a thicker head gasket on after the first set of seizures as I thought this may be the issue . The head gasket from the LI was extremely thin.

I have manually rotated the flywheel in both directions and it is smooth, quiet and does not catch anything.

I will strip the motor again and measure the bore clearance - do you know if the clearance can be measured from the piston crown down, or does it need to be measured from the skirt, up?

And I presume 0.15mm - 0.20mm is the figure that would be OK?

Sorry for being irrelevant but did you say that you have got a GT186 kit on a bog standard Li 150 S3 bottom end?

Cheers!

correct - the Li engine was entirely rebuilt by Diablo Moto, but essentially it is a standard bottom end. 1500 trouble free miles with the GT kit

Hi.Firstly,are you sure that the noise is coming from the top end,did you take the chaincase cover off when you got the engine,if the chain is very slack it could jam in the top chain guide.They are both Italian cases so I cant see the squish being so far out to cause it to stop,especially as you have replaced the head gasket with a thicker one.......................but then again !

I have to agree with HXPaul, if you have checked the top end out (the squish was a long shot) it is unlikey that your problem is there. As I said, it would not seize on tick over so that leaves rings snagging in the ports or gudgeon pin/circlip adrift but I'm presuming you checked those? Otherwise the sound has to be emanating from elsewhere, could something have got into the crankcase? Al Diablo knows his stuff so it is unlikely to be anything to do with the build quality tbh

Hi - to be 100% clear - Diablo Moto DID NOT build the engine I am having issues with.

The issue is with the DL i125 engine. Pretty sure its not crank case related. I will enlist a second set of ears to help me!

Next step to do as coaster suggests and check the rings & clips & pins

Any good news Covboy.
Cheers
Stag

HX Paul - it was chain case related. The rings, piston, bore, cylinder head etc all fine. I took it to Keith at reddoglambretta. Upon opening the chain case two gear teeth fell out. The suspicion is that the movement of oil upon start up was washing the stray teeth into the gearing and causing the engine to jam. 3rd gear also broken. 1 new gearbox and a rebuild later I'm ready to re-install and start again.

Bad luck there but @ least you have the initial problem sorted.

May I ask which gears actually got broken as I'm confused as to whether it was just third or, perhaps, first & third? Did the cluster suffer as well?

sorry

cluster gnarled and third

Covboy wrote:Last year I removed the cylinder, head and piston etc from my standard S3 Li 150 (fitted new, but about 700 miles / 6 months of normal use, no issues, ran well )

With the above statement from your opening post in mind, one had to wonder what was done to your engine in the intervening months to cause the gear teeth to shatter. Seems a little unlikely that they just fell off when you parked it up for the last time. Did you have the gearbox apart? did you use any sort of force on any of the drive components such as an impact driver, hammer etc?

Just wondering

Hi Coaster

The opening statement was meant to set the scene with regard to the known good components.

The next statement was intended to define the problem:
II recently bought a 1970 Italian DL125. The engine came without top end.. so I fitted the above surplus components from my LI + new 22m Scootopia carb, 42mm Clubman. Synthetic oil @3%. its also had new 12V electrics

Consistently the DL starts first kick, runs nicely for about 30 seconds, then a loud banging from the top end can be heard, followed by a seizure

The engine that I added the known good cylinder, piston & head to, was one that I bought with the GP - it came without a top end and was a unknown quantity to me. Rather than strip it down I thought I would just try it first (I am an optimist). I imagine that it was sold to me with broken gears, , but the seller did say the engine needed looking at to be fair....

sorry

cluster gnarled and third

That's a shame that an Innocenti GP125/200 gearbox has broken.

It's rare for a third gear to go unless racing, in my own bitter experience...

I'd bet that something way beyond normal 'wear & tear' occured there, especially as there is such little torque from the original top end.

If the cluster had lost a tooth off first gear in the first(!) place, it may have floated about to jam third. Even then, its the loose gear that tends to break first.

First gears often break through being crashed into gear upon bump starting.