big end shims

[cezeta]

ive got a 60mm mec crank from scooter centre with a yam rod, i had expected it to be shimmed when i bought it so was surprised that it wasnt and ive hesitated fitting it.

its being used on a gt186 kit

there are some conflicting views......what do the grown ups think?

[cezeta]

19 views but nobody knows....

[rosscla]

Ok here's my tuppence worth to get the ball rolling...

I'd have thought it should have been shimmed too. Contact the vendor and ask them. Maybe it's a mistake...

If it has a large float on the big end and you decide to fit it then you'll need to use piston shims.

The idea of either is to keep the conrod centralised on the pin and bearing, otherwise there's a potential for uneven wear or forces.

[gaz_powell]

i`ll put me head above the parapet !

i`ve have lam cranks with and without

I`ve got a rd400 rodded indian without ready to go in my next build (ts1 200 with yam piston)- the crank builder with years of experience was adamant that if the webs and rod on the original dont have them then not needed.
The rd400 rod came without them

I`ve got rd250 rodded mec 60mm with them in but the webs were machined to suit - sat on the shelf (built by the late Jon Betts)

Just done a rapido classic for a mate with sil crank, nrb bearing and sil rod without on the advise of another trusted crank builder - no side play as rod and webs not set up for shims

Ive just built a TS1 with indian webs and an rb rod kit - didn`t have shim with the kit again trusted crank builder said no need - no side play

i`ve got SIL webs with an af race rod kit in both my ts1 without - built by Chiselspeed - which echoes the above

i always use the widest small end available

af supply their rb rod kit without shims and i might stand corrected (said the man in the orthopaedic shoe) but i dont think they use them in their race cranks

i would have no hesitation in using any of the above as i trust the builders

i would be confident with a crank built by a reputable dealer - if there is no visible side play

interestingly both my mec and mazz in the vespas have them

yam rods are 1mm wider than SIL and AF which dont use shims - MEC use shims - all three been the same overall width - so in theory if you do away with shims at 0.5mm each on a MEC and use a yam rod without you shouldn`t have side play and you will achieve the correct size

there`s alot of differing opinion - its a mine field like everything lambretta

hope the above is of use and ps i`m not a grown up as my wife keeps telling me when i embark on the next project

gaz

[cezeta]

so it looks like the crank i have is a 60mm mec crank with the wider yam rod fitted with no shims which then fills the space.

mmmm, so if if use feeler guages then what is the accepted gap....max/min

[tavspeed]

hi all,i have just re-assembled my indian crank with a vespa ape conrod,i have pressed it together and have .3mm clearance between the big end eye and the inside of the web,giving .15 both sides,is this sufficient.
i scribed a line across both cheeks as a reference for re- assembling,now the width of the crank at the pin is 40.53mm,exactly opposite it is 41.06mm,i'm thinking of squeezing it in a vice to get the cheeks parallel,when i have the cheeks correct do i then check and adjust the run out,i have some vee blocks and dial guage to check it with.
also i am going to tig the pin,anybody any advice,i'm thinking of welding oneside,then getting run out correct,then welding other side,thanks all.


id not be happy at .3
.5mm to .7mm be better especially if the rod has plain sides with no lubrication cut outs
grind slots around the pin on opposite sides and fill with weld otherwise you grind clean therefore removing the weld
clamp the crank securely during welding and check after all is still true

id not be happy at .3
.5mm to .7mm be better especially if the rod has plain sides with no lubrication cut outs
grind slots around the pin on opposite sides and fill with weld otherwise you grind clean therefore removing the weld
clamp the crank securely during welding and check after all is still

recieved this advice off darrell taylor from a previous post,end of the day,there should be a protective oil film between the sides of the big end eye,if that film breaks down due to excessive heat,due to load or high rpm's,having shims or whatever wont save the crank,as long as side to side movement is not excesive you'll be good to go.

[Adam_Winstone]

Cezeta,

This thread has put a smile on my face and it is nice to know that I'm not the only one dwelling on such issues. I bought a MEC 60mm with Italian TV175 rod a number of years ago as the combo of long rod and long stroke is something that I like.... and they were being sold off cheap. However, it amused me to find that it had no big-end shims and SX/GP type side play, yet the small end is as per TV and not machined flat to take piston shims. As such, I didn't like the idea of the rod slopping from side to side so it too is on my shelf waiting for the day that I decide to do something about it (use or modify).

Adam

[drunkmunkey6969]

I find the whole crank thing a tricky issue, as there are so many brands of crank out there at different price points with hugely differing qualities, and so many differing opinions. You have to think about the BHP the motor will produce, as well as the way it will produce it, and at what revs....plus the interference fit of the pin, the length of the pin, the side float of the road, the thickness and quality of shims, the bearing /rod quality, the oil/lube slots, the web thickness/area around the pin, overall crank width within the mag housing, mag housing gasket thickness relating to flywheel position on the stator.......the list goes on!

Big end crank shims certainly help with increasing surface area for reduced friction and heat build up, but if clearances are too small then friction/heat build up is inevitable so you defeat the object of the shims! And to get sufficient clearance you then machine the webs, but subsequently reduce pin area and increase chances of twisting, so then you weld pins, and then people criticize about heat distortion......makes you want to give up!! lol

Before we built our own cranks i tried lots of 'branded' cranks, and two in particular were very good. But i also sent some Indian crank webs off to be re-rodded and new 'hi-load' bearing to be fitted, it was one of the best cranks i ever had, and didn't run shims.

I now build my own cranks using indian webs and Yamaha 110/116 rods, loctited pins and usually no shims. If the customer wants us to machine webs and fit shims, we can do that, and likewise we can TIG weld the pins too, but its not standard format for us. Each to their own, I'm sure someone else will have a differing opinion or experience....lol

[cezeta]

it keeps me up at night.......its the engineer in me, i cant accept maybe as i think in binary and arrange all the answers from the forum into logic gate patterns until i find a suitable and provable conclusion.

please help me.

[cezeta]

I find the whole crank thing a tricky issue, as there are so many brands of crank out there at different price points with hugely differing qualities, and so many differing opinions. You have to think about the BHP the motor will produce, as well as the way it will produce it, and at what revs....plus the interference fit of the pin, the length of the pin, the side float of the road, the thickness and quality of shims, the bearing /rod quality, the oil/lube slots, the web thickness/area around the pin, overall crank width within the mag housing, mag housing gasket thickness relating to flywheel position on the stator.......the list goes on!

Big end crank shims certainly help with increasing surface area for reduced friction and heat build up, but if clearances are too small then friction/heat build up is inevitable so you defeat the object of the shims! And to get sufficient clearance you then machine the webs, but subsequently reduce pin area and increase chances of twisting, so then you weld pins, and then people criticize about heat distortion......makes you want to give up!! lol

Before we built our own cranks i tried lots of 'branded' cranks, and two in particular were very good. But i also sent some Indian crank webs off to be re-rodded and new 'hi-load' bearing to be fitted, it was one of the best cranks i ever had, and didn't run shims.

I now build my own cranks using indian webs and Yamaha 110/116 rods, loctited pins and usually no shims. If the customer wants us to machine webs and fit shims, we can do that, and likewise we can TIG weld the pins too, but its not standard format for us. Each to their own, I'm sure someone else will have a differing opinion or experience....lol

so if i measure the gap on one side of the rod when pushed to the other side what should i expect or hope to see? its a shame mec 60mm cranks are not yam rodded out of the box, the rods are peanuts but not when you have to get it modified and rebuilt.

i think these could be the answer http://www.simplybeach.com/products/WAX ... Multi.aspx