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Author Topic: Project "walrus" Yam XS 750  (Read 29491 times)

Offline XS750AU

  • Posts: 251
Re: Project "walrus" Yam XS 750
« Reply #390 on: Jul 25, 2017, 08:17:20 »
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?
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N

Offline datadavid

  • Posts: 1069
Re: Project "walrus" Yam XS 750
« Reply #391 on: Jul 25, 2017, 09:07:33 »
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..
« Last Edit: Jul 25, 2017, 09:14:14 by datadavid »

Offline datadavid

  • Posts: 1069
Re: Project "walrus" Yam XS 750
« Reply #392 on: Jul 25, 2017, 09:14:54 »
Actually its nowhere close to redline on the vids, man, you should hear it at 9000....

Offline der_nanno

  • Posts: 203
  • Faster!
    • Greasy Greg
Re: Project "walrus" Yam XS 750
« Reply #393 on: Jul 27, 2017, 06:28:59 »
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
Real freedom starts with the freedom of thought.

My Blog:
http://greasygreg.blogspot.co.at

My Turbo TR1.1 (XV1000) build here on DTT:
http://www.dotheton.com/forum/index.php?topic=72571

My XS Triple Sidecar build here on DTT:
http://www.dotheton.com/forum/index.php?topic=74211

Offline Ryan Stecken

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Re: Project "walrus" Yam XS 750
« Reply #394 on: Aug 04, 2017, 05:01:11 »
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!

Offline XS750AU

  • Posts: 251
Re: Project "walrus" Yam XS 750
« Reply #395 on: Aug 04, 2017, 09:21:31 »
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.
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N

Offline datadavid

  • Posts: 1069
Re: Project "walrus" Yam XS 750
« Reply #396 on: Aug 07, 2017, 06:12:16 »
 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.

Offline Ryan Stecken

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Re: Project "walrus" Yam XS 750
« Reply #397 on: Aug 17, 2017, 04:40:53 »
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!

Offline XS750AU

  • Posts: 251
Re: Project "walrus" Yam XS 750
« Reply #398 on: Aug 17, 2017, 07:25:16 »
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.
“Engineering is the art of being approximately right rather than exactly wrong.”

Yamaha XS750-2D
Yamaha XS896
Husaberg FE550
Yamaha TT250
Yamaha IT200N

Offline Ryan Stecken

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Re: Project "walrus" Yam XS 750
« Reply #399 on: Aug 17, 2017, 07:30:33 »
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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