Crank

[special brew]

Running a rb 20 , like a div I've only been running at 3% , big end totally gone , when inspecting crank it as got realy hot around big end , would running at 3% cause that

[dscscotty]

AF Advise 4% on RB's, I tend to run 4% in all my motors, although I only use semi synthetic in road engines, my advice would be to run 4%, you'll never really know if this was the cause and without seeing the crank it would be hard to say,

[Warkton Tornado No.1]

Running a rb 20 , like a div I've only been running at 3% , big end totally gone , when inspecting crank it as got realy hot around big end , would running at 3% cause that

Presuming that the carburettor was well set up, fuel delivery to the engine @ full bore more than adequate & there were no air leaks, then it is likely the issue might be oil.

However, besides how good the builder of the crank was/rod/bearing type & quality, none of which can be presumed, big end lubrication failure really does depend upon the quality of the oil. Differences go beyond whether any two stroke oils are synthetic, semi-synthetic, mineral or castor.

What crankshaft & manufacture/type of oil were you using?

[MickYork]

How accurate was your 3% ?

There was a thread a while ago showing quite considerable difference's in the measuring jugs being used......just a thought.

[Fast n Furious]

As advised above.
it really does depend on the quality of the crank build as much as the lubrication used. There's a lot of cranks out there that just can'ny take it captain. Perfectly fine for shopping trolleys. No good with rev monsters.

[gaz_powell]

Out of interest what crank was it?

[a-teamlambretta]

Any damage to cylinder or piston other than the big end, just out of interest?

[special brew]

No damage to cylinder or piston , it's a mec crank bought from Glasgow lambretta , done under 1000 miles , running on exol premium semi synthetic

[Norrie Bodge]

1000 miles ? Is that all ?? & the BIG ends gone?
I’d be on the phone asking some Q’s m8
A lot of us guys here are using exol oils at 3%

A Mec crank has good oilways cut into the Conrod for the big end bearings lubrication

[holty]

i could be wrong but i belive that rayspeed recommend the silver cage high load big end bearing from suzuki rg for the rb application, to handle the high loads and revs, plus the lack of oil as some mixture by-passes the bottom end and goes straight down the boysen ports, i do seem to remember someone saying they had a big pile of scrap mec cranks, im sure they would be fine in a standard engine, but rb20 is well known as a rev monster so i think a high performance crank would be my choice, i always think of it as the heart of the engine.

[Solid Air]

No damage to cylinder or piston , it's a mec crank bought from Glasgow lambretta , done under 1000 miles , running on exol premium semi synthetic

I paired a brand new 60mm Mazzuchelli with a GT186 and was using fully synth Exol at 3%. The engine had a similar big end failure after about 3.5k miles last year. It was a brand new build and I'd like to think well built and set-up, the only thing we could attribute the failure to was lack of 2t lubrication(?).

[burnside]

No damage to cylinder or piston , it's a mec crank bought from Glasgow lambretta , done under 1000 miles , running on exol premium semi synthetic

I paired a brand new 60mm Mazzuchelli with a GT186 and was using fully synth Exol at 3%. The engine had a similar big end failure after about 3.5k miles last year. It was a brand new build and I'd like to think well built and set-up, the only thing we could attribute the failure to was lack of 2t lubrication(?).

I'm only running 3% Rock Oil Groundsman semi-synth in both my GT186 with GT 60/110 crank and GT200 with 58/107 MEC Crank, done over 5k miles on both without any issue and ride them both hard.

I also use the 'that's about right' method of adding 2T, so sometimes could be running at 2.5% other times 3.5%

Wasn't there a dodgy batch of MEC cranks a couple years back, where a lot of people were having issues, surely that couldn't have just been down to lack of 2T?

[Solid Air]

No damage to cylinder or piston , it's a mec crank bought from Glasgow lambretta , done under 1000 miles , running on exol premium semi synthetic

I paired a brand new 60mm Mazzuchelli with a GT186 and was using fully synth Exol at 3%. The engine had a similar big end failure after about 3.5k miles last year. It was a brand new build and I'd like to think well built and set-up, the only thing we could attribute the failure to was lack of 2t lubrication(?).

I'm only running 3% Rock Oil Groundsman semi-synth in both my GT186 with GT 60/110 crank and GT200 with 58/107 MEC Crank, done over 5k miles on both without any issue and ride them both hard.

I also use the 'that's about right' method of adding 2T, so sometimes could be running at 2.5% other times 3.5%

Wasn't there a dodgy batch of MEC cranks a couple years back, where a lot of people were having issues, surely that couldn't have just been down to lack of 2T?

I can't conclusively say it was the 2t but I couldn't pin it down it to anything else either, would be interested to hear views on oil lubrication and the big end...

[Warkton Tornado No.1]

Personally, I think that Rayspeed have really tried to avoid anybody having issues with their product, especially in this instance. This link is what 'they' have to say about the speculation about suitable big ends & lubrication:

http://www.afrayspeed.co.uk/index.php?page=Per_rb20

[holty]

Personally, I think that Rayspeed have really tried to avoid anybody having issues with their product, especially in this instance. This link is what 'they' have to say about the speculation about suitable big ends & lubrication:

http://www.afrayspeed.co.uk/index.php?page=Per_rb20

thats exactly the point that i tried to get accross in my post, they make the kit and develop them, their advice on components should be followed to avoid problems, i am very lucky and only live about 50 miles away so i can and do drop in to buy my parts and talk to scott and ben to get more info from them, not so easy for others as they are busy. the link you posted does state 4 percent and says about the uprated big end bearing, they do also state that they can upgrade your bearing as well.

[dscscotty]

The MEC crank, unless fitted with an RB type 18 Roller which is in fact an RG500 Bearing will not be up to the job, also if memory is right, I'm sure the last MEC-116 Crank I worked on had a 22.9mm pin, making it not suitable for upgrade to RB/Jap type upgrade. You'll need some webs that use a 22mm pin.
This is almost certainly why the crank has failed as it was not up to the spec required for a high revving Rb.

[Fast n Furious]

The MEC crank, unless fitted with an RB type 18 Roller which is in fact an RG500 Bearing will not be up to the job, also if memory is right, I'm sure the last MEC-116 Crank I worked on had a 22.9mm pin, making it not suitable for upgrade to RB/Jap type upgrade. You'll need some webs that use a 22mm pin.
This is almost certainly why the crank has failed as it was not up to the spec required for a high revving Rb.

+1
I don't believe there has ever been a 22.9mm bigend crank suitable for a reedvalved engine.

[special brew]

Ok , thanks lads, you live and learn

[gaz_powell]

Interesting chat as always, keeping the discussion going I have just had to replace the crank after big end failure in my TS1, which has given many years and fast motorway miles service , it was a Mazzachelli with 22.9mm pin and no shims - I certainly have no complaints, however I wouldn't go that route again, the replacement is SIL webs with RB Rod kit.

The Mazz crank has been rebuilt with a new stepped pin, a 15 roller NRB Big end bearing (from AF) and an older style Mazz race rod - built for a rainy day in something else , AF were confident that this would be okay in a TS1 but did stipulate not in an RB .

Gaz

[Norrie Bodge]

Yes good chat lads
So are these MEC cranks just a glorified std type crank, with a better Conrod & BIG end bearing?
or are they rated to perform ok to a certain BHP ??

Would they’ve fine used in the likes of a std Imola/monza/TS1 ???