Lambretta sx 150 soft seize after 7 miles

[bristolmod]

they do differ- see Stickies 2nd book page 81 for measurements.

I take the point that it may not be a "125" cylinder thats been rebored- could be anything on the top. 125; 150 or even a "proper" 175 cylinder.

Check the head as well- its not unknown for a cylinder to be bored out and the original then smaller head to be used!!


Chris

[10 inch Terror]

Source a genuine 175 cylinder and crank and you'll have a smooth reliable engine. Add a BGM, Gori or Clubman type pipe and bigger carb and you'll have a 65+mph scooter. It's a faff changing over the cranks granted but the benefits will far out weight the disadvantage.

[Donnie]

The OP says he knows nothing of engines, how much does he know about running in a scooter?

perfect chocolate brown?

At all throttle positions ie plug chops? And what plugs in it?

Running in on fully synthetic? That's going to take a bloody long time better off with semi, or if you know what your doing even mineral oil.

[garethwyn66]

Hi Guys
I am taking it back to scooter hub on tuesday and we are going to strip it to have a look will get back to you with more info.. all I can tell you is the engine work was done by super tune and it cost over a £1000 to do by previous owner.. thanks for your input ...

[Adam_Winstone]

First thing I'd do is retard the timing and richen up the jetting, then reconsider plug choice (none should really be a problem at this stage), then continue on your 900 miles of running in at no more than 34mph (or something like that according to the book). If you don't know the running in history then take nothing for granted.

[davet]

I'm not an expert on this by any means but there is a long list of things which can cause heat seizes. Ranging from dodgy boring either off centre (rapidos?)or too tight, wrong rings, timing, fuelling, air leaks and jetting. Just have to strip it, piston will give some clue and start from scratch. Don't forget even if an expensive rebuild has been completed at a reputable dealer, chances are some clown may have interfered with it afterwards.

If you aren't confident with your abilities, leave it to someone who can do it, or get someone to show you what they're doing to help you for the next time. Coz with Lammy's there will always be a next time!

[wack 63]

Nothing wrong with Rock oil injector mix,in fact probably better than the premix as it suspends in the petrol better unlike the premix that sinks to the bottom of the carb and tank. Once a top end seizes it really needs a strip down to remove any high spots as it will seize there again.

[Adam_Winstone]

"Have got the timing checked and it was out by 3 degrees. Set to 19 degrees.", which way was the timing out? If it was 22 degrees then yes, it was out. If it was 16 degrees then it was probably correct!

A pal of mine had his timing 'corrected' on his iron barrelled 175 that I'd set up for him to do a number of Euro Lambretta rallies reliably on, when it went into a shop to have a winter strip/rebuild to replace old oil seals, etc. Well, this correction of timing from 17 to 19 caused him to seize and break rings, 20 miles into our trip to Avignon last year! Recovery to the ferry port and an emergency strip and rebuild was needed before they let him onto the boat. A resetting of timing back to my 17 dbtdc marks on stator and mag housing on the French side then allowed us to continue without further issue, with one day of the return trip seeing us do 450 miles in a day (not bad on an iron 175 with 22mm carb and clubman).

If you read the recent feature on a tasty TV175 III in Jetset, the owner mentions resetting his iron Gori 200 from the recommended 21 degrees down to the more commonly used 19 degrees (more commonly used a few years ago) and then needing to further reduce to 17 degrees to stop it from getting hot and seizing. There will be plenty of people that state they are running anywhere between 19 and 23 degrees without issue (and I'm sure they are) , however, this is similar to 90 year-olds that still smoke 100 fags a day... it is possible but certainly is not the norm. Indeed, I know of plenty of people that are now running high compression kits at 16, 15 or even 14 dbtdc.

As already stated by others, there are lots... and lots... and lots of reasons for motors seizing, however, running temperatures will immediately be reduced if you retard the ignition timing. I would start by resetting the timing to 17 degrees and see if this cures your issue. Whilst I agree that top end strips and removal of high spots can be a good move, I'd be tempted to leave all else as it is and try the timing first. Personally, I like to identify and eliminate the cause of problems whilst the motor is together and running, so that you can be sure you've identified and cured the issue. If you strip and dress the top end before resolving issues then you're quite likely to still have the same issue when you put it back together... and then seize it again, ending up going round and round in circles.

It could be anything on a list as long as your arm but start with the most likely and easiest/quickest to resolve, which in my opinion is retarding the timing to 17. You will need the correct flywheel holding tool and extractor to get to the stator (don't try making do without these tools or you'll damage the motor) and you should really strobe your timing to check your new firing position. If you are in any doubt about doing this yourself then get help from someone who knows what they're doing.

Good luck with it.

Adam

[garethwyn66]

Hi guys the timing was out at 22 degrees that is advanced and after listening to your helpfull coments I have decided to get a standard 175 barell and head and fit a new piston and crank.. Hopefully the work will be done on tuesday when I take it back to mansfield. The Scooterhub. Just realy gutted i ve bought this scooter from a scooter dealer thinking. Rather than buying private it would have been the safest way to go as the scooters are sold fully serviced and road worthy. Obiously not. But must say the company s after sale service has been second to none so far. Hope this is my final run to mansfield as its a 7 hour jorney round trip. Will see what we find on tueday will let you all know. Thanks

[Adam_Winstone]

Good luck with the rework, I hope that it resolves the issues.

Adam