My shiny new Mec 60mm/110 rod Crankshaft doesn't seem to fit inside my 125 crankcase.
The main issue seems to be the con rod sticking out the webs by approx 1.6 mm, the clearance between the crank case and the Conrod when spun is less than 0.02mm (feeler gauge).
The webs seem to be rubbing a little which surprised me as the web diameters are within about 0.1mm of an LI crank.
I was wondering if other people have had the same issues and what the did about them?
My options seem to be
1. Machine the crank case to make it fit:- does this reduce the crankcase pressure.
2. Fit a new con rod onto the existing webs:- this has the advantage of a good jap conversion Conrod and bearing.
3. Buy a new crank that fits.
I'm open to options and advice.
Mec 60/100 crank recovery options
-
bristolmod
- registered user
- Posts: 1741
- Joined: Wed Jan 07, 2009 8:42 am
- Main scooter: Lambretta TV175 S3- what else!
- Location: Bali-Hai bar, Locarno Ballroom Bristol, 1967!- mines a Brown Split!!
- Contact:
sorry- not with you. Where exactly is the crank rubbing?
Scootering since 1968.
on the crank casing and the webs show marking after rotating the crank
-
bristolmod
- registered user
- Posts: 1741
- Joined: Wed Jan 07, 2009 8:42 am
- Main scooter: Lambretta TV175 S3- what else!
- Location: Bali-Hai bar, Locarno Ballroom Bristol, 1967!- mines a Brown Split!!
- Contact:
nothing as simple as the crank fouling on the main bearing plate is it? I rebuild a TV175 engine a bit back and had a similar problem. Had to get a shim from MB to fit between the crank and the main bearing to move the crank over a fraction. I've dismantled dozens of engines over the years and never came across this before, but there is an "official" shim sold to correct this.
Chris
Chris
Scootering since 1968.
-
bristolmod
- registered user
- Posts: 1741
- Joined: Wed Jan 07, 2009 8:42 am
- Main scooter: Lambretta TV175 S3- what else!
- Location: Bali-Hai bar, Locarno Ballroom Bristol, 1967!- mines a Brown Split!!
- Contact:
Scootering since 1968.
Unfortunately it's not that, the diameter of the crank + extra bit caused by the Conrod is too big for the diameter of the casting.
I either reduce the diameter of the crank or increase the casing diameter.
I either reduce the diameter of the crank or increase the casing diameter.
-
olliewtf
- registered user
- Posts: 229
- Joined: Thu Feb 06, 2014 1:08 pm
- Main scooter: Lambretta Li S3
- Contact:
dont take metal off the big end it will only weaken it.
this is common on 60mm cranks, not all, but some.
grind a channel in your crankcase till the big end clears on full rotation.
and dont worry about losing crankcase compression, it will be very marginal i imagine and either way the benefitd of 60mm will overshadow this.
goood luck and make sure your are meticulous cleaning all the swarf out!
this is common on 60mm cranks, not all, but some.
grind a channel in your crankcase till the big end clears on full rotation.
and dont worry about losing crankcase compression, it will be very marginal i imagine and either way the benefitd of 60mm will overshadow this.
goood luck and make sure your are meticulous cleaning all the swarf out!
Depending on the advice I was intending to pay the local machine shop to have 0.2-0.5mm machined out but I really need to know what's an adequate clearance
-
olliewtf
- registered user
- Posts: 229
- Joined: Thu Feb 06, 2014 1:08 pm
- Main scooter: Lambretta Li S3
- Contact:
i achieved it using my dremel. not pretty but it functions. couldnt tell you what a decent clearance is, but on e thing i did notice was that its more at the opening of the mouth on the top and bottom where it will need the most work, as opposed to the full circle if that makes sense.
in terms of which is best, one costs more but looks neater, one looks a bit diy but is cheap. also allows you to check and recheck if oyu have sufficient clearance, as opposed to going to the shop, getting the work done, finding out its still binding somewhere, and having to go back.
its your choice at the end of the day, but i im not convinced someone will give you the answer you need, as all cranks are different.
in terms of which is best, one costs more but looks neater, one looks a bit diy but is cheap. also allows you to check and recheck if oyu have sufficient clearance, as opposed to going to the shop, getting the work done, finding out its still binding somewhere, and having to go back.
its your choice at the end of the day, but i im not convinced someone will give you the answer you need, as all cranks are different.
On mine it seems to be the full circle where the clearance is minimal, that what left me confused!
Others have said that a small amount needs to be removed at the mouth which I expected and was prepared to do, but I can't get it to spin freely at all hence the need remove more material.
I intended to take casing and crank and get someone to open the whole casing bore up to match the crank, but it seems a bit drastic.
Or get it rebuild with a better con rod.
There seem to be pros and cons for both
Others have said that a small amount needs to be removed at the mouth which I expected and was prepared to do, but I can't get it to spin freely at all hence the need remove more material.
I intended to take casing and crank and get someone to open the whole casing bore up to match the crank, but it seems a bit drastic.
Or get it rebuild with a better con rod.
There seem to be pros and cons for both