Yamaha Tuning Advice

Mariner91 · 05 July 2018, 10:43

Hi all,

Due to failed crank seals and bearings, my yamaha 50 has had to come apart.. Whilst I'm this far into it I'm thinking about doing a few bits to tune it up a little..

I am thinking of looking at the following:

70hp carbs (If anyone knows of any for sale...)
CCM / Boyson Reeds
Milling cylinder head down by 1mm
Shortening exhaust 'tuner'

The important thing here is that I want to keep the engine reliable and useable day to day - is any of this a good idea?

Cheers
Jack

A1an · 05 July 2018, 18:25

Rolfhat on here is your man

http://www.rib.net/forum/f50/my-thundercat-61912.html

Roflhat · 06 July 2018, 11:40

Sounds like a good plan, the 70hp carbs take quite a lot of tuning to get right though, personally I'd just stick to the standard carbs.
Carbon reeds are good, also means you won't damage anything if they do break. You can have a look at the Hydrotec website for ideas on what the exhaust tuner should look like, they also offer phase kits for the yamahas.

Chris Applebee Engineering are who I use for the cranks, they're good but they are very expensive. Maybe worth balancing your crank + flywheel seen as they'll be apart anyway. They'll tell you how strong the press on the crank is, if it's weak then have it welded, will give you peace of mind. Can also remove the rev limiter, I think it's the grey wire looping from the CDI box if it's the same as the 70hp

Mariner91 · 10 July 2018, 23:39

Cheers Seamus,

I've also just replied to your Pm, much appreciated!

Something I have noticed is that the Top crank bearing is by far the worst and was completely dry of oil when I stripped it. It was mounted with the sealed side facing up towards the flywheel and the open side pressed tight against the crank.. How is oil supposed to get to it?

I looked in the manual, but I'm my way of looking at it, it contradicts itself (see pictures).

Unless anyone is aware of any reason why, I'm tempted to put the new one on with the open side facing up towards the flywheel, at least that way it'll stand a chance of getting some oil in it?

Davie · 11 July 2018, 05:21

I think you have confused yourself where the barb fitting is that the oil injection hose attaches to. The bearing is open at the bottom side. Hth

Mariner91 · 11 July 2018, 06:16

Quote:

Originally Posted by Davie

I think you have confused yourself where the barb fitting is that the oil injection hose attaches to. The bearing is open at the bottom side. Hth

Sorry, I don't quite understand what you mean by this? I'm wondering how yamaha expect oil to get Into the bearing when the open side is pressed tight against the crankshaft?

Roflhat · 11 July 2018, 07:26

I don't think it will get any oil with the open side facing up, then the open side sits flush with the top of the casing so it definitely won't get any? I see what you are saying though, my best guess is that oil must get to it between the open face and the crank, although maybe not as much as neccassary hence the poor wear

At least the top bearing can be pulled off without taking the crank apart, so even if you do have to replace it more often it's not such a big job

Davie · 11 July 2018, 13:23

Quote:

Originally Posted by Mariner91

Sorry, I don't quite understand what you mean by this? I'm wondering how yamaha expect oil to get Into the bearing when the open side is pressed tight against the crankshaft?

The oil will get into the bearing in the same way as the oil will get into the big end. If you put the sealed side of the bearing down the way petroil cant get into the bearing.

Mariner91 · 15 July 2018, 10:45

Thanks all - crank is away being rebuilt now and I'll be putting g the top bearing back on in the correct orientation!

Mariner91 · 20 July 2018, 01:10

Got the crankshaft back from being split - not especially happy though.. Firstly they damaged the worm drive and told me someone had taken it apart before and filed it..

It's obvious that they have slipped off with the puller and damaged it.. Not that I was going to use the oil injection but I'd prefer to not be lied to..

And for some reason they have put the bearing that I posted about just above on upside down after all that!

So it looks like I'll have to go to the effort of changing it myself or driving all the way there and back twice again anyway..

(perhaps this is the punishment I get for not going with the reccomended firm, but another otherwise highly regarded one that could turn it around much quicker)

Thankfully everything else: measurements between the webs and runout etc. are all in spec...

Before:

After: