Cowboy cylinder porting

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johnny650
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Well the parts arrived today so I finally managed to get my engine leak down test done and it didn't take long to discover the source of my leak.... its one of the base transfer ports.
The outer edge of the right hand side transfer port can clearly be seen to have absolutely no gasket surface that can mate with the transfer port of a standard small block crankcase mouth.

A previous owner of this cylinder has hacked the transfer ports presumably because he read somewhere that there can be power gains by opening up the transfer ports on cylinders and crankcase mouths ...........or perhaps because someone bought him a Dremel for Christmas :roll:

Its a great pity that those people who talk about porting work don't include a few lines of text giving owners some basic instruction about how to go about such work .

When carrying out any porting work on cylinders and manifolds and crankcases its essential that ports are matched together first to clearly mark safe maximum limits to ensure that after the ports are opened out there is still sufficient gasket surface area left to form an effective seal . Its not rocket science .. :roll:

A simple method is to spray paint a base gasket and mount the cylinder and head . When the cylinder is removed you should have a clear indication on both sides of the gasket of the extent of the mating surfaces of both cylinder base and crankcase mouth . This will show the limits of how much material can be safely removed from the ports.

One of these days It will finally dawn on me that there is no such thing as a 'bargain' or 'saving money' by purchasing someone elses used parts on eBay. What you are frequently buying is someone else's problem component that is either damaged , poorly constructed or simply doesn't work as intended. :roll:

If the previous owner of this 185cc cylinder kit is reading this I can only hope that, like me, he also wasted weeks of his precious time searching for the intermittent hard starting and poor running issue before he also did a leak down test.
Shame on you for selling the kit on to another fellow Lambretta owner

C:\Users\johnny\Pictures\2018-08-16\lambretta 185cc over porting 1.JPG
[img]C:\Users\johnny\Pictures\2018-08-16\lambretta 185cc over porting 1.JPG[/img]
johnny650
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[img]C:\Users\johnny\Pictures\2018-08-16\lambretta 185cc over porting 1.JPG[/img]zero editing time again I see ?
C:\Users\johnny\Pictures\2018-08-16\lambretta 185cc over porting 1.JPG
C:\Users\johnny\Pictures\2018-08-16\lambretta 185cc over porting 1.JPG
C:\Users\johnny\Pictures\2018-08-16\lambretta 185cc over porting 1.JPG
http://i130.photobucket.com/albums/p261 ... m0yery.jpg
B-Race Tuning
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Johnny, be aware the cylinder may have come from/ was matched to, for example, a Spanish casing with tons of meat around the crankcase mouth to suit said "over" porting, or even set up with a 110/115/116 rod. Utilising a packing plate (even a 3mm for 110 rod) the cylinder transfer ports at the base can usually be opened up beyond the meat of a standard casing. All of which the previous owner may not have been aware of out of ignorance of spec.
Then again, it could be just ignorance? (unable to see photos).
?????
Simon.
johnny650
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thanks for the reply Simon. I gave up on trying to post an image i'm afraid.
I cannot use my Flickr account and Photobucket links don't seem to work on here for some reason.

Interesting about the extra alloy around the crankcase mouth It hadn't occured to me . I knew that some Spanish small block cases were the same spec as the large block and are much sought after but I never thought about it being ported to match a Spanish case. Its a Scooter Restorations 185cc cylinder kit apparently.

There is zero gasket support on the outer edge of one of the transfer ports so I decided to create some artificial support by using a 1mm alloy base gasket .

This morning I put the engine back and did a leak down test and bingo !...no more leaking Yippee..
Squish measures 1.45mm which surprised me . I expected it to be 2mm+

I got it started and it ran well for about a minute until it ran out of fuel. I had forgotten to turn it on .......

Since then it has refused to start and it is clearly way too rich. i have a great spark so no problem with the ignition.

I will jet up a spare Jetex carb and try that in the morning. I am absolutely knackered from kicking it over for over an hour .

I could do with a starting point for a 185cc with 22mm jetex and 42mm AF Rayspeed clubman.
I am currently using 50 choke 45 pilot 5899-2 Atomiser ,... 118 main jet and a 150 slide .
I'll probably try a 112 main jet next
johnny650
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B-Race Tuning
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I can see those photos, yes it does look a little thin for your casings doesn't it. The "artificial" support does work. If you take that further, (other than using a longer rodded crank[costly]), It is possible to get a machine shop to take the gasket face at the base as far up the cylinder as the fin (£30?), using the fin as the gasket face and a packer to match material removed+ 0.25 bringing squish sweet to give you the gasket area to make long term safe. (Not too different to the top/tailing done with these cylinders to use a suzuki piston). Looking at your inlet port it would look like previous "tuner" 'ported' only the base of the cylinder. There's a heck of a lot of potential in those cylinders. Make sure measuring before machining that it will bring your transfers/ inlet timing to desired figures. Oh, and don't assume 3/4/5 mm plate is 3/4/5mm, get it and measure thickness first, the numbers are nominal, not exact (3mm could be 2.8-3.2)
johnny650
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thank you B-Race thats very good advice and assessment.

Yesterday I re-fitted the cylinder on a 1mm Alloy base gasket with Threebond .
and carried out a Leak-down test ........Zero leaks at last !...

Squish is now 1.45 which is quite acceptable for the time being .

Unfortunately I still cannot get the damn thing to start and run reliably. its been 6x long weeks now and I still cannot ride it ....

I have great compression , good strong consistant spark, I advanced the spark from my usual 19 degrees to 17 degrees , It now seems to be over-rich .
When the plug is dried it will usually start with no choke and run briefly but it very soon starts to bog down and then dies. Plug is wet on removal and excess fuel in hose and on plug.

Next step this morning I'll replace the choke valve and spring and ensure no possible choke leakage.
i'll reduce the Main jet to 112 and the Pilot jet from 50 to 45 .
I'll also swop the 200 slide for a 150 and see how that goes.

The frustrating thing is it has run extremely well one time only for about half a mile even with air leaks at the base gasket and a missing drive side oil seal ?

I'm very close to dumping the scoot in the back of the garage for good............ All my neighbours are sympathetic but you can tell after 6 weeks of watching me strip and rebuild the engine and hours spent kicking it that they think I'm completely clueless and wasting my time.
I need to get this heap of *%$£ running soon if only to salvage a little dignity.
Adam_Winstone
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First thing is not to trust anything Jetex for jet size as they are frequently miles out. JETEX bodies are often fine but can also be problematic.

If you're using Dellorto jets and atomized then I'd look no bigger than 45 for pilot and imagine that you may find the 5899-4 (GP150) atomized cleans up the bottom end nicely, HOWEVER, you will then typically want to go bigger on the main to balance the progression toward higher throttle positions. Choke tests will help you to test jetting.
johnny650
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yes you are so right ..... I too never trust anything ....old habit. I use jet sizing tools in conjunction with a vernier guage
I have an extensive collection of 6x jetex carbs and dozens of jets, atomisers but every combination I have tried so far hasn't given me reliable starting and running . I'm beginning to think it may have something to do with the clubman which I bought used and untested

This is a 185cc cylinder with 42mm Clubman so I expected to need more than a 5899-4 atomiser but I'll try that next.
My Li150S ran faultlessly on 5899-2 atomiser 45 pilot and 108 main jet and standard 38 exhaust.

Imageorganiser 1 by John, on Flickr
Scooterdude
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I noticed on your other tread that you only have the mixture screw out 1 turn, try 2 full turns and see if that is all thats needed.
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