Scooterotica

Hey! I have a crankshaft question, mostly regarding the use of piston shims or not. Story is- I had a gp crank with 22.9 crankpin. I bought an AF "reverse" stepped crankpin, 22.9 for the webs and 22 in the middle for the bearing, with special bearing. I had the webs machined, fitted a 115mm yamaha rod to it, used 0.30mm big end float upon assembly, but....omitted the big end shims, as 22mm shims will not fit over a 22.9 step.

My question is that without the big end shims, should I be using small end shims to align the rod? Or, as with original early cranks, just use the big end clearance I have to keep things straight? There's certainly more surface area for the bearing to catch and keep oil with the yamaha rod vs stock. Also, using a wiseco ts185 piston.

I have Indian GP200 webs and an RD400 115 Conrod. I was told by the professionals that pinned and balanced the crank that it was good to run without thrust washers. I also have no small end shims but, as with yours, there's little side to side movement at the big end anyway.

I have one the same as Storkfoot ready for my new TS1 200 with IT 17T piston - no shims tolsd the same by the crank builder -

i will be using a wider IT/DT small end bearing with it

gaz

Thanks guys! I figured i would run without piston shims, but just wanted other opinions. Yeah, I'll be running the wider little end bearing too!

[quote="gaz_powell"]I have one the same as Storkfoot ready for my new TS1 200 with IT 17T piston - no shims tolsd the same by the crank builder -

You will love that motor

Found this on FB and it settles the argument. Unfortunately I didn't use shims, maybe the later SIL webs are harder but I doubt it.

try to keep my finger on the pulse and keep on top of forum questions. Sometimes it's boring and nothings happening the questions are boring and stupid and sometimes I'm infuriated at some of the comments from the know it all p155 taking pricks. Lately there's been some right nobs having ago at MB over the smallest of descriptions on our web site or some thing they heard made up down the pub pissed up once way back that was incorrect in the first place! Then there's the know it all's giving advice from biker type people who's never ridden a Lambretta! In the last few weeks there's been a few crank questions, one that pops up is 'should I fit crank shims to a Yamaha con rod conversion and can I use a wide Yamaha small end bearing'? And all the experts quote the experts saying no need. Well seen as I invented this conversion 28 years ago you could say I know a little bit more than these none scooter riding experts or experts who haven't done the mileage or supplied a large number of customers. In the early days to gain width in crank webs to take the wider rod I tried con rods without crank shims. Guess what these cranks came back to me where the rod wore into the crank webs and over heated the rod, turning them blue and big ends suffered. To get around it I tried to reduce the amount of friction on each rod trust side and guess what they failed as well. I then used 0.5mm shims and guess what we saw some of these warp and fail and moved to the 1mm shims which in 20 years I've never seen a problem. Today because of crank pins and crank designs it is common to have to use 0.5mm crank shims. And the question develops can I use a wider small end bearing? Who found that in the first place? Ok lets look at these things, a con rod needs centralising. This can be done in 2 ways, 1) crank shims line up the con rod, then you can do what you want to the small end bearing providing you do this correctly. 2) you can line up the con rod with the piston. In the photos you can see some cranks that's come in this year for me to do and yes they have been fitted with after market rods and yes the rods have worn into the webs, run them like that for long and the rod and bearing will pack in. This is made worse with the Yamaha rods as the small end area is narrower than a standard Lambretta con rod and a Yamaha con rod can never centralise using a Lambretta piston and it's made even worse using a Jap style piston. The Lambretta con rod was used to line up the crank with no shims. The only after market rod used with the standard small end is the AF con rod. With this rod you can use it with no shims, providing it is fitted with a piston like our MB Race-Tour piston where it is designed to run the standard width small end bearing (20mm) and no piston shims. If the rod is say 19.50 – 19.90mm wide the rod is centralised by the piston and the big end side thrust wont wear out the crank webs (providing there is clearance) But the AF rod is 107mm and totally limits how an engine can be set up so we have stuck to the 100/115mm Yamaha con rods since the 80's. Using the piston and piston shims is old Innocenti designs. Today modern engines don't do this they use shims on the big end and lets the small end move around as it's needed. Arrrhhhh ….... So the question is why do I write my articles on the Tech-Site? Does any one read them, does no one listen, or do people think I make these things up, do I not have more experience than the grubby biker type down a wooden shed? I wouldn't mind but over the years people are still giving false advice which is dangerous and all I'm trying to do is offer the best service and advice to help you Scooterists out.

Lol, I believe Marks response is directly linked to rhe question

Sent from my GT-I9300 using Tapatalk 2

What are big end shims made from?
Steel?
Hardened Steel?
Or a bearing material such as Bronze, Aluminium?
Just curious.

SF

I don't know what they are made of but they look like aluminum in colour, at least the ones I've seen. Although, MB kindly pointed out this error I wonder if anyone has not used shims and had many happy miles. My crank has no shims and the motors runs well but I don't fancy the idea of stripping it down to check if the Yam rod is wearing into the web.

"...And all the experts quote the experts saying no need...."

Bit harsh, never said I was an expert

Well, having taken the advise of long time bike crank builders on two occasions, I'm knackered on both my TS1 with .5mm thrust washers on a Kawasaki conrod, and my GT186 with no thrust washers on a Yamaha conrod.

I'm no engineer but common sense tells me thrust washers would be good engineering practice. So, Mark is right But, the TS1 crank has been in for over 3 years now over many thousands of miles without a blip. The GT186 has, unfortunately, only done 1500 miles and is now without a scoot to run it in

I suppose time will tell.