Project "walrus" Yam XS 750

Thanks data!
I´m currently collecting information on which parts will be available...some oil seals (part numbers:93102-24154, 93103-50103) are also not available which is for me a big NO NO...i´m always doing all seals gaskets when I do a motor....

Next up will be doing the cylinder head:

How do I make sure that this head is the later "better" more horsepower XS 750 head?What are the differnces to the old head design?

Already bought the right tools and fresh viton valve stem seals, grinding paste and all the good stuff 8)

Since its my first time (regrinding and checking valves) could anyone point me in the right direction,already watched a few good videos on what to do and not do, but I´m pretty sure there is more to it :D?

First step will be removing the camshaft (checking for signs of wear), and valve buckets with shims.
Then I will use my spanner tool to slowly push down the valve springs, removing the little retainers.
Next up check the "side lash" of the valves in the valve stems.
Checking the valve seats for chipping and wear.
Regrinding the valve seats (using little grinding paste, NO paste should go into the valve stems) by hand.
My manual says that I must measure the fresh grinded new valve seat surface and see if its in spec.
Reassembly-->check for leaks with gasoline
Start NEW or call it a day :)
 
Re: Project "walrus" Yam XS 750

I think there is a difference in the combustion chamber shape, i think my heads had either domes or little domes around the valves. Supposed to aid breathing and combustion. The xs11 also has these peculiar multi-dome shapes.
Like this:
5d34d6cb973f83a7f86556f12081173b.jpg
 
You don't grind them, just lap them. Max. seat width on valve and seat, see manual.

Generally, if it's more than 1mm you've got to get the seats recut and the valves re-faced. (This is a rule of thumb-value, but in general you're pretty much on the money with this one...)
 
Re: Project "walrus" Yam XS 750

datadavid said:
I think there is a difference in the combustion chamber shape, i think my heads had either domes or little domes around the valves. Supposed to aid breathing and combustion. The xs11 also has these peculiar multi-dome shapes.
Like this:
5d34d6cb973f83a7f86556f12081173b.jpg
+1 for the combustion chambers and cams are the major changes on the later heads. Sorry don't have a photo of the head on my other bike to compare with.
 

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Found some not so good photos of a 2D head online. You can see that it does not have the twin chamber. The twin chambers reduced the combustion chamber volume, hence increased the compression ration.
 

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Re: Project "walrus" Yam XS 750

....looks like the PO sold me the "better head" for a normal head :-(....my bad I should have not trusted him....looks like I will need to run with the normal heads.
Will the 825ccm piston and cylinders be compatible with the old heads?

Cheers
914683e64d6cbd074476458d00f01c47.jpg
 
Re: Project "walrus" Yam XS 750

No problem using that head on a 825. You will get a higher compression with the larger capacity relative to the fixed compression volume.

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Re: Project "walrus" Yam XS 750

XS750AU said:
No problem using that head on a 825. You will get a higher compression with the larger capacity relative to the fixed compression volume.

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Thank you!
Just checked my 825cc pistons are just a few millimeter bigger than the 750?


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Re: Project "walrus" Yam XS 750

Too bad my late heads have all been eating valves.. i could weld up and reshape the polyspere shapes, but a lot of work, heads are easily found for these bikes.
 
Re: Project "walrus" Yam XS 750

datadavid said:
Too bad my late heads have all been eating valves.. i could weld up and reshape the polyspere shapes, but a lot of work, heads are easily found for these bikes.

Dave - has the same issue happened on more than one head? Can you put is down to any particular reason? From the videos it does look/sound like you are pushing the redline!
Now I could be wrong, but I think the compression ratio when bored out to 896cc would be up around 11.5:1. Does anyone know if that could affect the durability of the valves?
 
XS750AU said:
Dave - has the same issue happened on more than one head? Can you put is down to any particular reason? From the videos it does look/sound like you are pushing the redline!
Now I could be wrong, but I think the compression ratio when bored out to 896cc would be up around 11.5:1. Does anyone know if that could affect the durability of the valves?
Haha, they came like that in the parts lot!
Last registration on my bike was 1984 sometime, and the leftover pistons were for over 1000cc bore. No oil cooler found anywhere, and probably no deep sump was used either, my guess is it overheated and blew up. At least twice!
I think my machinist calculated the compression to 10.5:1 actually, se talked about skimming the cylinders to raise comp, but i wanted to be able to run 95octane pump gas. My cooling is so good it almost takes too long to reach operating temp, thinking about switching to the shallow sump actually..
 
Re: Project "walrus" Yam XS 750

Actually its nowhere close to redline on the vids, man, you should hear it at 9000....
 
You'll just loose a bit of compression-ratio, but it will certainly work.

Have a look around and try to source an 850 head or a late 750 head, if you're really concerned with the power-output.

Cheers,
Greg
 
hey guys!

so I´ve done a bit of searching on the interwebs and found this head in the UK,alltogether with cams...ould you guys take a look if its buyable:

http://www.ebay.de/itm/YAMAHA-XS750-XS-750-CYLINDER-HEAD-CAM-CAMSHAFTS-/322483449021?hash=item4b1582ecbd:g:jMYAAOSwCWFY8Lt3

thanks in advance!
 
You should be prepared to spend some money on it if you buy it. Looks like it has been exposed to water and it is impossible to know how much damage has been done from the photo.
The good is, it is the correct head casting and all the cooling fins are intact. One exhaust stud is missing and could be stripped, easily fixed with a helicoil. The cam lobes look good but obviously the cams have been removed at some point. Just hope they are the original cams and have not been replaced with earlier cams???? It would be good to see the journal surfaces for wear.
From all the carbon build up in the exhaust ports and valves the engine was cactus, so I would have expected more marking on the cams. It is a bit like the triumph carbs I bought, be prepared to spend more that you paid for it to get it serviceable. At the least you should budget for new guides and valves.
 
Re: Project "walrus" Yam XS 750

Worst thing that can happen to it is if its ran out of oil at some point, you really dont want to repair that, otherwise, to get max power and service life from it, change guides and valves, and recut all valve seats. You also want to get new valve springs.
 
So I decided to run the "old" head for now...I will dissasemble this weekend and post some pics.I can still swap out for the "better" head down the line...

I have a question for you guys:

There a few screws missing on my motor (screwed from down below),do you guys have measurements and/or pics of these screws?

I marked them red in the pic.

Thanks!
 

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Ryan
You are lucky as they are only a standard M8 flange head bolt grade 8.8. Not sure of the length, so I will check on the weekend. The journal bolts are specialised OEM bolts that are far more difficult to source.
 
Re: Project "walrus" Yam XS 750

Thank you tim!

A question on measuring the tolerances of the crank:
Bought some red plastigauge and finally got the right torquw wrench to go down on the bolts.
Am I right that when I place tze plastigauge on the surface (how much of a strip would you place?) that its suffice to tighten the 4 journal bolts?

Thanks in advance!

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