Showing posts with label Engine. Partial strip and full rebuild details. Show all posts
Showing posts with label Engine. Partial strip and full rebuild details. Show all posts

Sunday, August 23, 2020

Engine. Partial strip and full rebuild details

Firstly, in all the years I have been scootering, the one area I have left alone on Lambretta's is the engine. I have never had the need to break open an engine casing as I am lucky enough to have a few of the very best builders in the country on my doorstep.

My best advice, if you are reading this blog in order to assist you to strip a scooter, is that it is likely you won't have the knowledge to strip and re-build a Lambretta engine. That's not to say you can't. Everything is possible. If you have engineering or mechanics skills, then it may not see to be quite a challenge to you.

BUT, you should bear in mind that when you take the engine apart, you will need to know if bearings are worn beyond repair, have the tools for the job and be able to recognise damage to gear cogs, chains, layshafts and so forth. With this in mind, if you are confident, then there will be a link at the end of this section to show you how a professionally built engine is put together. Taking it apart is the same, but in reverse.

What I have done here, is strip the engine casing of most of the parts (where possible) and I am then going to have it professionally re-built. I know it will then be safe for the new owner, have the correct components fitted AND come with a guarantee of workmanship.

Here's what I have done with the engine so far...

This engine appears to have been stood for many, many years. And if this project is anything to go by, taking it apart will fight me every step of the way. Usually, a simple job like removing the rear wheel takes under a minute. Not on this scooter. On your machine, underneath the large nut in the centre of the wheel is a locking plate with 2 or three holes. In one of them, will be a grub screw that goes in to one of the three holes you can see below beneath the washer. On this bike, it is missing and a normal washer has been used. This means that the rear wheel has been overtightened, squashing the washer and almost welding itself to the hub. I simply don't have the correct tools to remove it, so i will simply remove the wheel rim from the hub and leave it in place for the dealer to remove and thus, hopefully prevent any damage I might do attempting the almost impossible.

To take off the cowlings attached to the engine, you need to remove the exhaust unit. First, undo the two large bolts (or studs) at the upper front end of the scooter engine.

Then, look under the engine for a "tab" on the exhaust that is bolted to the block you can see in the picture below.

And finally, the tail of the exhaust should have a ring clip attached to one of the side casing bolts (or
studs). As you can see, the majority of the tail part is missing from this scooter.

Normally, at this point, you should be able to remove the exhaust silencer section from the downpipe attached to the barrel. however, as usual, this one is seized together, so the downpipe will have to be removed with it complete.

So now we will have to remove the cylinder head cowling to get at the exhaust manifold. Take out the spark plug if fitted.

Look at the edge of your cylinder head cowling, it is fixed via 2 bolts to the mag housing and one bolt right in the centre of the cowling. remove all three.

Now you can ease the cowling forward a little, enough to expose the exhaust manifold attached to the barrel. It is attached by bolts on two studs as you can see in the image below.

Removing them can be a bit fiddly, but luckily, these came off OK.

As you can see, there may just be a little bit of rust and dirt in the exhaust port.

But with the exhaust removed, you can now take off the cylinder head cowling.

Next, the flywheel cover should be removed. It is normally attached to the flywheel housing via 4 bolts, depending upon your model, there may also be holes for rubber grommets, which assist with anti-vibration. On this scooter, the bolts have all been replaced with oversize screws and will have to be ground off and then professionally removed.

With them all off, the housing can be pulled away.

Removing the cylinder head is simple. Remove all 4 bolts and make a note of the position of the larger one. This is hollow and threaded on both ends to allow the large bolt that holds the cylinder head cowling to be threaded in to it.

This is the position of the larger bolt in configuration with the engine.

With all 4 undone, you can take off the cylinder head. If it is in good condition, it can be re-profiled and the barrel honed or re-bored. So be careful not to damage the fins or join surfaces.

The barrel is locked on solid. The piston is seized inside and is not going to move for me. Another job for the experts. However, I'll press on removing parts that CAN be used again after cleaning.

Remove the two bolts holding the carb manifold.

Remove the two bolts holding the clutch and gear cable adjuster housing. You can also remove the gear linkage, gear selector arm and brake arm. Circlips hold the latter two in position.

Remove the rubber, engine bump stop. Simply pry it out with a screwdriver. Under it, there should be a thick washer. Don't lose this.


Remove the circlip from the rear brake arm and pull away.

That's about it for me with the engine. The rear drum is almost welded on, the barrel is seized and the kickstart pedal was missing.

So, because this engine is going to be totally re-furbed with new parts by the dealer, i might as well stop. In any event, it is going to have a brand new 12 volt electrical system, so the flywheel and stator plate are going to be replaced, uprated crank, seals, bearings, chain etc. might as well let the pro's do it.

If you want to continue with yours, scroll down.

Here is an excellent piece, written for the Lambretta Club of Great Britain by Rick huggins.
My sincere thanks to him for putting this together for us. It shows you EXACTLY how to re-build your engine and all the tools required for the job. My advice to you is to get advice before you start. If you can afford it, let the professionals do it, but if you feel good about it, go for it!