What did you do today? Cobba's rebuild

[cobbadiggabuddyblooo]

I hope the info on the pistons is of help that I sent you Brett.. Sanddunes 51 (Mark ) has the oversize OEM yamaha pistons in his bike. He may have some info on how much gap (.030"?? ) he has between the piston and top of the barrells to get that little more compression from the std 10.5.. I know I'm safely limited to .048" so if you go down the route of the OEM oversize pistons, he may have some input and info to gain the most from your rebuild in this respect as all these factors may have an input to your valve timing..
I'll try to get some pics of the std and JE pistons as a comparrision and the STD cams and kent cams...

[Rod.s]

I hope the info on the pistons is of help that I sent you Brett.. Sanddunes 51 (Mark ) has the oversize OEM yamaha pistons in his bike. He may have some info on how much gap (.030"?? ) he has between the piston and top of the barrells to get that little more compression from the std 10.5.. I know I'm safely limited to .048" so if you go down the route of the OEM oversize pistons, he may have some input and info to gain the most from your rebuild in this respect as all these factors may have an input to your valve timing..
I'll try to get some pics of the std and JE pistons as a comparrision and the STD cams and kent cams...

Mate i seem to remember that the factory limits were 0.030-0.048mm, but i have looked through the manual and can't find the info anywhere, so it must have been a dream

With yours we'll have to assemble everything and then plastigauge the clearance and go from there, what fun, i just can't wait

[M.V.]

What did I do today? Nothing that interesting!

Good work guys, good to see the inside bits that I haven't seen yet

[Trixed]

Cobba let me know if u need a hand tomorrow. Happy to help. Might come over and have o look anyway. Couple a beers on a lazy Sunday, priceless!

[cobbadiggabuddyblooo]

I hope the info on the pistons is of help that I sent you Brett.. Sanddunes 51 (Mark ) has the oversize OEM yamaha pistons in his bike. He may have some info on how much gap (.030"?? ) he has between the piston and top of the barrells to get that little more compression from the std 10.5.. I know I'm safely limited to .048" so if you go down the route of the OEM oversize pistons, he may have some input and info to gain the most from your rebuild in this respect as all these factors may have an input to your valve timing..
I'll try to get some pics of the std and JE pistons as a comparrision and the STD cams and kent cams...

Mate i seem to remember that the factory limits were 0.030-0.048mm, but i have looked through the manual and can't find the info anywhere, so it must have been a dream

With yours we'll have to assemble everything and then plastigauge the clearance and go from there, what fun, i just can't wait

No you weren't dreaming Rod.. was in the info I had gathered and was showing you in the front of my folder ..Those specs came from TTS... But better to be safe and make sure we get it right first time and I appreciate your attention to detail (personally I wouldn't approach this myself without it ). We should have built up a wealth of info, specifications and photo documentation by the time we finish.

[cobbadiggabuddyblooo]

Todays time was spent between Yum Cha , looking at Pats thumb that he put through the rear sprocket while trying to clean the chain. And checking through the paperwork to make sure I have everything within it's tollerence, oil pump came up well within it's tollerences and as Rod explained this is where you'll find a drop in oil pressure and the same on the crank journel bearings if not close to the lower tollerence. Next was to check the run out on the crank and came in with .002 so I'm a happy chappy once again.


Next thing for me to get my head around was the crank and rod bearings.

So first off was to deal with the crank and make sense of whats written above and after a couple of minutes it all fell into place.
Looking onto the crank I found the numbers stamped onto the crankweb... Then time to go the the engine case and look at the numbers stamped there. I always wondered what these numbers where about. I thought someone had individually stamped the cases as a security measure But you never stop learning, there reference numbers for the main journel bearings on the crank.


So a little simple maths and look at the bible and all confirmed what colour bearing to be used and where abouts.
The 2G refers to the Conrod bearings being 2GREEN next pair of numbers 4,5 being the crank bearings with No.4 being green and No.5 being yellow and the last 3 numbers being the reference to work out what colour bearing to the crankshaft being used and numbers on it... So if you change crankshafts you can worrk out from these 3 numbers on the case and the last 3 numbers on the crank what colour bearing to use...



The top 5 numbers are from the crank with the first 2 numbers refering to the conrod bearing size...
the next 3 numbers refering to the crank journels...
This is where it became apparent that if I'm getting new conrods I have to wait till I find the numbers stamped on them to work out what colour bearing I need from the table in the manual..
And if you pull the motor down and cant see what number is on the conrod just work backwards using the table by looking at the colour on the bearing and the crank number will give you the number on the rods

As for the crank I have all the info I need with the last 3 numbers on the crank and the three numbers etched into the engine case . With the crank coming up all fine I can utilise the same colour bearings. Those being green yellow green...

[BigAl-TC]

OUCH

[cobbadiggabuddyblooo]

yer I was goin to add as for the last digit... I mean thumb.. I wondered why Pat didn't show up Sunday about a week ago so I could fit the Akrapovic cans to his Hornet900..
He was holding the rag in the palm of his hand and pressing it up on the chain from underneath. But the rag got caught and his first reaction was to put his thumb down on the chain to stop the rag and as he realised what he'd done it was too late but had his other hand on the gearlever and knocked it straight out of gear. So lucky it only found it's way an inch or two up the rear sprocket..... SO DON'T TRY THIS AT HOME KIDS

[sanddune51]

Hey Guys! I was enjoying this thread til I saw the thumb. Hope it mends as fully as possible who ever owns it (had to skip reading at that point as I'm pretty squeamish )

Any way back to the bearing shell selection. Great post covering a topic that I don't believe has had much coverage here in the past.

Mark.

[Snod Blatter]

I was hoping someone else would ask so I don't have to look silly but.. What do the colours mean?

[Rod.s]

I was hoping someone else would ask so I don't have to look silly but.. What do the colours mean?

Well they are purely a reference for you to fit new bearing shells.

Quick explanation...
A/
1, the crank is ground using a high speed fine grinding stone, then a secondary super fine stone and finally a polishing stone.
2, these stones wear as they are used
3, the resulting bearing diameter grows (from nominal) as the stones wears
4, after a production run the crank bearing diameters are measured, using (old school) a go/no-go gauge. Modern using a laser....
6, http://en.wikipedia.org/wiki/Go/no_go_gauge
5, the bearings require a gap between the crank and the bearing (this clearance measurement can be found in the repair manual, 0.020-0.038mm)

B/
1, the case and the bearing caps are bolted together and line bored to ensure that they are all perfectly aligned.
2, these are then measured using a go/no-go gauge

C/
1, we now have three dimensions, crank diameter (a), case diameter (b) and clearance (c).
2, b-(a+c) will give us the total thickness of the bearing shells
3, divide that figure by 2 will give us the thickness of one shell,

Yamaha, have a table that has a thickness range for the shells, eg 1.000mm - 1.015mm this range relates to a colour eg yellow.

4, the workshop assembler will correlate this range to a colour and select the bearing shell to suite.
5, the bearing shell has the colour printed on it side making for easy identification.

D/
1, the dimensions "a" and "b" are converted to a base number,

Eg 39.00mm - 39.015mm = 1
39.15mm - 39.030mm = 2
39.30mm - 39.045mm = 3

These base numbers are stamped on the crank and the case.

Yamaha won't tell us the thickness/diameter of the bearings or shells etc, all we get is that "number"

So we take the crank case number, say 4 and subtract the crank bearing number, say 2, 4-2=2, number 2 in the manual tell us that the bearing should be a "black".

Hope this helps.......

The issue with replacing conrods is that this same process is done for the rods. So if we replace the rods we'll have to wait until the new rods arrive before ordering the bearings as the rods will have their unique "number/letter" and we need that to do the simple formula.

If you replace the rods using "carrillo" rods, you will need to assemble the rods and using "plastigauge" determine the clearance gap and then order the bearing shells from Carrillo to suite, this is great as you can reduce the clearance to optimum, but at a considerable cost.

Unfortunately or fortunately, depending on how you look at it, we don't know the tolerance of the bearing supplied by Yamaha, making it hard (but not imposable) to tighten up the clearances by using small internal dia bearings.

For example, the limit of a "black" bearing may be 39.005mm - 39.010mm and the "brown" limit is 39.010 - 39.015mm. The bearing gap (between bearing and crank journal) is 0.020-0.038mm, so we really have a tolerance of 0.018 (0.038 - 0.020 = 0.018mm) or +/- 0.009mm.

If we measured the crank journal and it was 39.008mm close to the upper limit of a "black" shell BUT really close to the lower limit of the "brown" bearing, we also have an oil clearance tolerance of 0.018mm meaning we could use a "brown" shell also as this is still within tolerance!

So what do we do? well $ is what you need. if your cranks main bearings are marked yellow and green as Cobbas are, you buy the next smaller (dia) bearings, brown x 2 and green x1 in this case (he has two green and one yellow), then fit them using plastigauge to determine if the clearance is within tolerance! If the smaller (dia) are within spec then you can fit them, if not go back to the factory fitment recheck using plastigauge and make a decision.....then we get into crank grinding etc.

Simples

[Snod Blatter]

And here I was thinking they could surely grind them all the same by the nineties, silly me! Thanks for the explanation though

[sanddune51]

Thanks Rod,

That must be best explanation of bearing shell selection I've ever read .


Mark.

[coxylaad]

today I sat beside the pool for a while, then got up and got a glass of coke, then repeated this for the most of the day - its a hard life

[sherlock]

Had you moved the bottle of coke closer to you, then you wouldn't have had to get up.......