If you are a serious engine builder then you’ll appreciate the importance of keeping your crankshaft clean while the cylinder and piston are removed. Standard practice was to “stuff a bit of rag in there” to keep out dirt while the top-end is off. That never really works too well because the con-rod extends past the gasket face and remains vulnerable to dirt and corrosion.
Sticky has recently been developing an inexpensive solution to help keep your crankcase sealed whilst an engine is unsealed. Various versions are available for most popular Vespa & Lambretta models and others are planned. Here’s all you need to know about this nifty £6.99 part.
What is it?
The Crankcase Mouth Cover (CMC) kit is a 3D-printed plastic cover for your crankcase. It has a conical section to accommodate the rod, allowing it to sit flat against the gasket face preventing dirt from entering the engine.
The CMC is held firmly in place by the supplied plastic tubes fitted to the studs and retained by the original cylinder head nuts and washers. If you want a perfect seal then you can add a greased or silicone-coated base gasket before fitting the CMC.
When would the CMC be of use?
- To protect your crank and seals while your cylinder is rebored or re-plated
- When you need to store or transport an engine without the top end fitted
- Any time you weld, paint or grind in the same workspace as an open engine
- Whenever you want to clean a crankcase without removing the crankshaft
- While working on an engine in dirty, windy conditions (race track or garden)
- When you are working with the engine in the scooter and dirt is liable to fall from the chassis into the motor
Which models are currently covered?
- Lambretta 200 engines (Innocenti, Serveta, SIL etc)
- Lambretta 125/150/175 engines (Innocenti, Serveta, SIL etc)
- Vespa Smallframe (V-series and PK)
- Vespa 200 (PX and Rally)
- Vespa 125/150 (PX and older models with M7 studs in a rectangle)
- Vespa T5 (with M8 studs in a rectangle layout)
- Lambretta smallframe (Lui, Vega, J-range, Cento etc.)
- 3D print means custom modifications and new versions are always possible.
What is included in the CMC kit?
- The 3D printed plastic CMC cover. This is a solid plastic part produced in PLA which is resistant to fuel and oil. It is printed at high-speed on-demand in various designs to suit a wide range of scooter and motorcycle engines.
- Four pre-cut to length plastic tubes used with your standard head nuts and washers to hold the CMC firmly in place.
What is CMC made from?
It’s printed using a plastic called PLA+ which is easy to print, and made from renewable sources.
Are there any limitations to the use of CMC?
PLA+ is resistant to oil and fuel so it should provide a good seal. The only limitation is that it softens at relatively low temperatures (around 60 degrees C). Do not fit until your engine has cooled down. Do not weld in proximity to the CMC or it may melt.
Can I use a CMC while washing my engine?
Yes, but if you want a perfect seal it’s better to use a greased paper gasket or better still a bead of silicone instant gasket. Do not directly jet-wash around the CMC.
Why is the top surface of my CMC not flat?
The only important surface of the CMC is the bottom gasket face which should be perfectly flat to ensure no leaks. The top surfaces are printed using a large nozzle for speed of production. This creates a rougher outer surface but also a stronger part.
I have a problem with my CMC – it doesn’t fit!
If you have a problem please email me before contacting anyone else and I’ll try to resolve it.
I need a CMC for an engine that isn’t listed
We are happy to make CMC versions for other models of vehicle. If you need one for something that isn’t listed, please contact us. If you send a base gasket we’ll do our best to design a CMC and add it to our range.
Additionally, if you require a custom modification – for example, a CMC for welded-up and enlarged casings, then we should be able to help.
Price and availability
CMC is currently only available directly through eBay priced at just £6.99 plus postage. There’s also a workshop multipack containing six different CMCs for £29.99.
Sometimes the simple ideas like this make us wonder why nobody else has ever thought of them. The CMC is a perfect way to seal an engine and at £6.99 we can all afford one.
Additional photos: Sticky and Tony Higgs
The CMC concept is registered (and priced affordably enough) that there should be no need for unauthorised copying.
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