Big End Bearing colour (again) discrepancy

[Bellerophon]

Hi All,

So I have still got my engine in pieces and although the big end bearings are still in tolerance (just!) and aren't too scuffed up , I may as well replace them. I followed the instructions* to find the colour in the manufacturer's and Haynes manual and I need 2x Brown bearings. The bearings in there also look like they have a brown marking. So all should be good right?

However, eBay and cmsnl.com have the bearing codes listed with a different colour to that in the parts list (http://www.xs400.com/attachments/yamaha_xs400sh_parts_catalogue-pdf.8985/).

For instance on the cmsnl.com website (I have linked the codes to the webpage):

• 36y-11656-00 - shown as Purple, should be Blue
• 36y-11656-10 - shown as Blue, should be Black
• 36y-11656-20 - shown as Black, should be Brown
• 36y-11656-30 - shown as Brown, should be Green

I emailed them querying this and they said:
"There seems to be a discrepancy with the catalogue and the actual parts. The XS400 catalogues all have different description with these bearing. While other models have the description correct with the colours. We've checked all our stock and this matches the pictures we have on the website. I'm not sure how we can solve this issue. Sorry I can't be more of service."

So finally, my question is:
Do I go off the original parts manual and go for the Brown "36y-11656-20" or use the 'new' colours and buy "36y-11656-30" ???

Also, I understand the codes are to do with the bearing thickness - does anyone know which direction the thickness goes between codes? ie is '00' the thickest and '03' the thinnest or vice versa?

If anyone can offer any insight, it would be greatly appreciated. I am going a bit dotty with this.

*I am not going to go into the method, as there's plenty of info out there on how to determine the colours for your setup & don't want to distract from the issue, sorry.

 

[NewHavenMike]

Usually the last digits indicate the oversize.

36Y-11656-00

36Y is the model prefix. 11656 means something like the specific part type/size, this is usually a generic number within Yamaha parts. You will see parts that have 11656 in the part # and be for a completely different bike and have a different prefix, made in a different decade, until the part was superseded and obsolete. The 00 will indicate the oversize. Seeing a 10 or 20 will mean that its .010" over or .020" over original size.

Ive had trouble finding parts for my bike, which has the 1L9 (1976 XS360C) prefix. When the XS400 came out, 1L9 was essentially made obsolete and only a few parts carried on into the 400 until the part was superseded and replaced with the next prefix, which most likely became a 2L0 or 12R, among a few other prefixes. 36Y carried on into the late 80s in the FJ1200.

Honestly, you may have opened a can of worms. Bearings are very very hard to find and if you do, youre getting one half of a plane bearing thats been opened and was tossed around in the pile for years and years. If the bearings dont show signs of foreign material and arent galled, continue to use them. Opening the bottom end of an old motorcycle engine is always the last resort. Never do it because you want a piece of mind or "while youre in there".

I havent needed to look up engine parts like that in a long time now, but I had a lot of trouble finding bottom end parts. The crank bearings always confused me too but I didnt need to replace them, even though I did research to find them. What I found was half shells and old opened misplaced bearings that had no part # because the packaging was lost and someone had written the part # with a marker on a post-it note.

Maybe your experience will differ from mine, youre overseas and many of the parts I had to acquire were from places like Germany, Japan, and England, everywhere but the USA basically lol

You will need to measure crank/bearing clearance with Plastigauge and go from there

 

[Bellerophon]

Wow, thanks for all the information Mike that really helps.

The 00 will indicate the oversize. Seeing a 10 or 20 will mean that its .010" over or .020" over original size.

So just to be clear the bearings get thinner and the bore gets bigger as the numbers go up?

Opening the bottom end of an old motorcycle engine is always the last resort. Never do it because you want a piece of mind or "while youre in there".

I'm actually doing a 250 to 400 conversion, so a full rebuild was pretty much on the table anyway. I probably could have got away with not taking the crankcase apart but after the amount of gunk I found in there, I'm glad I did.

Maybe your experience will differ from mine, youre overseas and many of the parts I had to acquire were from places like Germany, Japan, and England, everywhere but the USA basically lol

Haha, I've had the complete opposite problem, all the eBay listings I find are in the US.

You will need to measure crank/bearing clearance with Plastigauge and go from there

I did do a plastiguage test, I can't quite remember the measurement but they were just in spec still. I also only tightened the big end bolts to the minimum torque spec as I understand these bolts are meant to strain harden when tightened. To be fair they are not in bad nick, I may take your advice on board and just keep them as is. I will try and post a photo later. I am still replacing the case bearings as these are worn.

Honestly, you may have opened a can of worms.

So it sounds. It's a bloomin minefield!

 

[Bellerophon]

So managed to take some photos. I know it's tricky but what do you think?

 

[xschris]

Remember that rod bolts are a one time use. They need to be replace with new one after a full torque happens. Use the old ones for your plasti gauge test then new ones for the re-build.

 

[Bellerophon]

Remember that rod bolts are a one time use. They need to be replace with new one after a full torque happens. Use the old ones for your plasti gauge test then new ones for the re-build.

So says the Haynes manual (and it says you may need to replace them) but the Yamaha manual doesn't - unless you have seen otherwise?

It's kind of a moot point tbh as they are as rare as hen's teeth / rocking horse sh*t. I think I will go to the maximum torque (or one over) and hope for the best.

 

[xschris]

Keep in mind the pressures these need to take every time the piston goes up and down.

 

[lhaolpa]

Been a while since I was on [illness and an old Fart].but you could take the rods to a machine shop if you could find one and have them checked for hairline cracks. You'll probably have to find a race car builder that actually builds engines rather than just throwing parts in. I have a '82 xs 400 rj DOHC that I've had in mothballs and will start building it,probably into a rat bike soon. Good luck !!

 

[NewHavenMike]

Using my phone so my response is limited for now. There was a set of ARP bolts that should be compatible with our conrods. They were for a Mitsubishi car. Not sure if they work but ill look into them.
250 cranks are a bit lighter in weight so that may be beneficial.

 

[lhaolpa]

Any GOOD automotive machine shop could measure the rod bearings and order some. A check with plastigage will tell you if they need to be replaced. Having said that,any time I open up the lower end of an engine,if I don't know better I replace all bearings and seals.

 

[Bellerophon]

Any GOOD automotive machine shop could measure the rod bearings and order some. A check with plastigage will tell you if they need to be replaced. Having said that,any time I open up the lower end of an engine,if I don't know better I replace all bearings and seals.

Sadly, in the UK we don't really have that many automotive machine shops.

 

[lhaolpa]

If you have access to a micrometer,you can get the thickness,width and the size of the crankshaft and get a bearing from the interweb. You'll need to get an idea of clearance and allow for that. I once rebuilt an old engine that had bearings that had to be poured and machined for clearance. I adapted it to modern bearings,so most anything is possible. There is,somewhere in the archives,a reference to an alternate part from a British sports car engine that has similar bearings. It has been a long time since I read it,but maybe someone,maybe Drewpy that will remember it. Try to find a shop that works on old Leyland stuff. Good luck!

 

[NewHavenMike]

So just to be clear the bearings get thinner and the bore gets bigger as the numbers go up?

Crankshaft refinishing involves regrinding the bearing surfaces on the crank to a mirror finish, resulting in less diameter on the crank. The bearings are oversize to make up the difference.

Im pretty sure the 400 cylinder will only fit to a 400 and late 360 case. I found this out when I bought a square block 400 cylinder to fit on the 360. Ive never seen a 250 around here but Im thinking the sleeve holes would be quite a bit smaller than the 400.

I would use the 250 crank in the 400 and a US spec 400 cam.

With the connecting rod bolts, I dont know if I would risk reusing them. There was a thread here about the ARP bolts as a replacement.

 

[Bellerophon]

If you have access to a micrometer,you can get the thickness,width and the size of the crankshaft and get a bearing from the interweb.

I have measured the crankshaft for ovality with a mic and it is still in spec - I couldn't find the shaft size listed however. I don't really want to go down custom bearings tbh, I think it'll be safer to carry on with what exists.

Crankshaft refinishing involves regrinding the bearing surfaces on the crank to a mirror finish, resulting in less diameter on the crank. The bearings are oversize to make up the difference.

Thanks. Not to be a pedant, but if the crankshaft is ground to a smaller dia. the bearing would be undersize not oversize.
I have dry fitted my XS400 (round) cylinders and head to the XS250 casing and it fits well. Also the camshaft and head are identical.
I'll have a dig with ARP and see what I can find.

 

[lhaolpa]

I have measured the crankshaft for ovality with a mic and it is still in spec - I couldn't find the shaft size listed however. I don't really want to go down custom bearings tbh, I think it'll be safer to carry on with what exists.



Thanks. Not to be a pedant, but if the crankshaft is ground to a smaller dia. the bearing would be undersize not oversize.
I have dry fitted my XS400 (round) cylinders and head to the XS250 casing and it fits well. Also the camshaft and head are identical.
I'll have a dig with ARP and see what I can find.

I think that the confusion comes from the fact that the bearing thickness is greater and the ID is less,thus the undersize. I would think that Yamaha would use established sizes of parts in a lot of similar sized bikes,with some having overly robust parts,others simply adequate.

 

[NewHavenMike]

Bellerophon

What youre saying makes absolute sense and now Im confused haha.

http://www.xs400.com/threads/xs400-budget-build.15972/

ARP kit # 107-6002

I dont know if that user had success with them. The instructions for the bolts give you a little bit of a choice. You can tighten them by measuring stretch or torque them to the ARP spec.

ARP specs 26 lb/ft and my XS manual specs 23.9 lb/ft - 27.5 lb/ft.

I do not know if these will fit.