I stepped in it - XS750/896 build

datadavid

Over 1,000 Posts
XS750AU said:
Hi Tom
Nanno (If you search you will find his blog on this site) used 3 x Mikuni TM carbies to work on his XS750 sidecar. I think they were 36mm, but it was a lot of work, a real lot of work!! You have to figure out how you are going to get 3 carbie cables going into 1 throttle cable. And then you have the issue of 3 individual chokes - how do you activate them. You can only reach 1 of the 3 choke plungers. It has been done but Nanno has put his TM carbies on the market and is now using others that are more simple.
If you get a set from a Triumph 900 triple they basically fit straight in.

The Cruising Image pistons are meant to be made in Japan not China, but who really knows, they are what they are. As long as you have them and give them to the shop that will bore the cylinders on a proper rigid set up there will be no problems.
My machinist was pretty certain they (cruzin pistons)were not chinese. He would not have touched them if he thought so.
Some guys are picky..
 

der_nanno

Faster!
Hi Frenchtom,

Nanno here... Honestly: Don't do it with the individual VM/TM carbs. They work a treat, but sync'ing is a nightmare. Also I went with 36mm carbs and they were too big. I am currently running a heavily modified set of flatslides out of a snowmobile, but even then, simply getting Triumph-carbs is a way simpler method of doing things AND a whole lot cheaper. (See the link to my sidecar-thread or maybe on my blog, if I forgot to post on here with regards to how much work the flatslide carbs took to get going...)

That being said: Cruzin-Image is Taiwanese and as they seem to come from one of the big automotive engineering companies, they only contain a very small portion of recycled soda can's and what else was lying in front of the factory. Haven't used them on the XS-Triple, but on a Zed recently and yes, they are fine indeed. Tell you machinist to clearance on the tight side of stock pistons and you'll get lots of life out of them.

Frenchtom said:
Maybe rearsets although I do not want to lose kick start capability. I may need it with the high compression 896 kit, the starter may not do the job.

Take the starter apart and clean it from all the graphite dust on the inside. Plus add a NEW ground and live wire (get the cables made at a welding shop and tell them to solder and shrink wrap the ends as per specification for welders in humid climate, IIRC IP54 that is in American nomenclature) and you should have no problem whatsoever to start the bike. If needs must, the Honda CB900/1100 Bol d'Or run a 1.1kW starter, but if you add hotter cams anyway that will take away quite a bit of the dynamic compression and the engine will spin over just fine.
 

Frenchtom

New Member
So I dropped off the cylinders and big bore pistons yesterday at the local machine shop. Should get those back in a week or two.

I have been thinking about this whole carburetor thing and was wondering if buying a set from a 4 cylinder 1200cc bike would work? I would only need 3 of them on my 900cc engine and could use one as a backup spare. If this might work, what would be some models to look out for or avoid?

Thanks!
Tom
 

datadavid

Over 1,000 Posts
Frenchtom said:
So I dropped off the cylinders and big bore pistons yesterday at the local machine shop. Should get those back in a week or two.

I have been thinking about this whole carburetor thing and was wondering if buying a set from a 4 cylinder 1200cc bike would work? I would only need 3 of them on my 900cc engine and could use one as a backup spare. If this might work, what would be some models to look out for or avoid?

Thanks!
Tom
I think it would just be a matter of finding bikes with the right cylinder spacing. Fuel feed might be an issue as well as most 4 cyls will have t fittings between carbs 1-2 and 3-4.
Triumph carbs have a single inlet between carb 2 and 3 and makes life easier in general. Look for keihins at bike scrappers.
 

der_nanno

Faster!
Hi Tom,

do yourself a favour and get a set of Mikunis or Keihins for a Triumph Triple. You'll at most end up spending 50 extra bucks on the carbs and save yourself hours of hassle. I will build another set of flatslides for the XS-Triple in July, but Triumph carbs will definitely be cheaper.

Cylinder-spacing on the triple is even, so no carb-set out of a fourcylinder, that I have ever laid my hands on will match straight away, as they are usually 77-85-77mm spacing. (Except for some Honda Bol d'Ors and some of Yamahas FZR-line!)
 

XS750AU

Coast to Coast
Triumph carbs have a single inlet between carb 2 and 3 and makes life easier in general

do yourself a favour and get a set of Mikunis or Keihins for a Triumph Triple.

I totally agree with this advice. The standard Mikuni BST36SS from a Triumph T300 are working perfectly on my 896 after they were rebuilt. The Mikuni's are much cheaper, due to their reputation about the slide guides wearing. But parts are available. Buying the carbies and the parts to rebuild them, cost me about AU$300. which is very reasonably for what you get.
 

Frenchtom

New Member
So I removed the valves from 2 sets of heads that I have. I noticed that on my black colored head, the exhaust valves had a bit of play in them as I removed them from the guides. The intake valves had no discernible play at all. On my silver colored heads the exhaust valves had less play in them than the black heads but one of the intake valves had the slightest bit of slop. I am thinking new guides are in order no matter which head I use. How hard is it to replace valve guides?

I was thinking of smoothing out the intake and exhaust runners but after looking at them I cannot see and real opportunities. Both runners are real smooth and clean. Any advice on what I should do here?

Also, what should I look for on the valve and seats when it comes to damage or problem areas? What are some things I should consider now that the heads are apart - re-machine or polish the seats, polish the back sides of the valves, clean everything, etc.?

Thanks,
Tom

First pic = black head
Second pic = silver head
third pic = intake runner
Fourth pic = crud on exhaust seat
Fifth pic = valve tool on bench
 

Attachments

  • P1030359.JPG
    P1030359.JPG
    2.8 MB · Views: 308
  • P1030364.JPG
    P1030364.JPG
    2.8 MB · Views: 313
  • P1030363.JPG
    P1030363.JPG
    2.6 MB · Views: 295
  • P1030360.JPG
    P1030360.JPG
    2.8 MB · Views: 300
  • P1030358.JPG
    P1030358.JPG
    544.4 KB · Views: 297

der_nanno

Faster!
Both inlet valves need a bit of play in their guides or otherwise they will seize up, once used under normal running conditions. If you pull out the inlet valves and have them 5-10mm off their seats you should have a forward and aft play of about 1mm. If you're not sure, whether the guides are worn, try moving them left and right. If you have (about) the same play in that direction as well, then the guides and valves are still good. If not then your should have a closer look. Usually the guides will have gone towards and oval shape, if worn. This can be seen very well if you put a light under the head, so it shines through the guides.

With regards to touching up the ports, as the pictures show, there's quite a bit, that can be done to these, but I have the nagging suspicion, that this would be your first go at porting? (no problem, just asking)
 

Frenchtom

New Member
Hi Nanno - yup, this would be my first time. But luckily I have two heads in case I screw one up so I would like to try some king of porting although I am not seeing what you see as far as opportunity goes. These ports look pretty clean to me but then again, I am no expert.
Tom
 

der_nanno

Faster!
No problem.

There's basically two schools of thought on how to port an engine.
1) increase port speed
2) increase amount of flow through the port (volume basically)

Unfortunately 1 and 2 contradict each other. Because the bigger the port gets, the lower the speed. Which incidentially is also the reason why installing a HUGE carb on a small port won't work. (Because the vacuum created in the jet's orifice will be weaker...)

Luckily the above only partially applies to your problem, as you don't plan to go berserk on the poor port, but just improve what's there. In this case this means, to knife-edge the bosses around the valve guides, so the air flows nicer around them (increasing speed and decreasing turbulence in the port. The second part will be clear up the area BEHIND the valve stem as you want to slow down the air-fuel mixture, but leave a knife-edge separator to help aim the gasflow towards the combustion chamber. What you want to end up with is a teardrop-shaped boss around the valve stem, with a small knife-edged ridge going to the back. (on the inlet) The walls on the inlet-port can do with a gentle touch up with a mini-flap-wheel on a dremel, but DON'T polish it as that will actually be counter productive.

On the outlet all you want to do is to knife-edge the boss and blend it in towards the valve guide. The exhaust port can be polished, but it's more to give you that warm-fuzzy feeling of having done something to the exhaust port as well.
 

Frenchtom

New Member
Hi Nanno and thanks. I understand everything you described although "knife-edge" is a bit interpretive. I found the following image and I am thinking that this is what you mean?

Also, do I remove the valve guide or leave it in when I do the machining work? I have an air tool set and plan to use flapper wheels and maybe a grinding stone if I am feeling confident. More than likely I'll stick with some kind of sandpaper based bit.

Tom
 

Attachments

  • exhaust.jpg
    exhaust.jpg
    41.4 KB · Views: 937

der_nanno

Faster!
Hi Tom,

yep, that gets pretty close. The line on the front is called a knife edge and depending on port design, it can be more or less prominent. Keep in mind, that the port you're showing here has the valve-boss sitting almost perpendicular to the port, whereas it is more countersunk on the XS. You leave the guide in and at best (for a first try) don't touch it. Remember you have to do this in an equal way three times, so best keep it (relatively) simple at first. Also in the port in the picture, they decided to go with lots more volume (and thus a lot lower port speed), as they could then directly reach the valve, shortenning the distance dramatically the gas has to travel through the port.
 

XS750AU

Coast to Coast
I don't want to dampen your enthusiasm, and it is great that you have 2 heads and can afford to experiment with one and not worry about losing a head.
I started having this debate when I was building the 896. The debate about gas speed vs volume worried me as I was not experienced with porting. I was all for opening up the exhaust port but was warned about reduced exhaust gas speed affect on ultimate power. In the end I just cleaned up the ports and polished up the exhaust side.
The gas flow on my XS896 has been improved by Mikuni BST36SS cabies and using triumph 1050 header with a shorty can.
It pulls hard to redline in all gears and does not run out of puff, it runs out of gears! So I am not sure that you will actually get any measurable/felt improvement by porting alone?
Both your heads are the later design which is good and provides a higher compression ratio, and more aggressive cam timing.
Sure give it a go, but without carbies and header work you may be a little disappointed.
 

datadavid

Over 1,000 Posts
I just sanded off some casting imperfections in my intake ports to decrease turbulence and it wheelies in first, no clutch and body weight forward, so it must have worked!
 

Frenchtom

New Member
Hi guys and thanks for the input. For some background, I just want to try my hand at machining the ports and make some marginal improvements since I probably won't have the interest once the bike is reassembled. I am going to do some other speed shop stuff like getting the pistons and rods all the same weight and try to balance the crank. My goal is an above average, smooth running bike although pulling wheelies in first gear sounds like a lot of fun!
Tom
 

datadavid

Over 1,000 Posts
Since it does that basically untouched, who knows what a mild port job can do? I just got the advice from several people that it looked quite good and just needed some light smoothing on the casting surface, but it can definitely be improved.
 

Frenchtom

New Member
Well folks - a bit of progress this weekend. I got the engine pulled from the frame and will begin dismantling the whole thing next weekend. I also got my cylinder back from the big bore conversion. I am thinking I should have cleaned the outside of the case before getting the bore work but I can still do the cleaning, just need to be extra careful. I also weighed my pistons on a drug dealer scale accurate to a gram. I thought I had 3 exact weights in a row on my piston assemblies but wouldn't you know it the last one came in 2 grams light and now I have to lighten the first two. I verified that the weight difference is in just the pistons. I'll check the rods for equal weights when I get those pulled and try my hand at balancing the crank on some air-fed bushings. Should be fun!
Tom
 

Attachments

  • IMG_0189[1].JPG
    IMG_0189[1].JPG
    1.6 MB · Views: 293
  • IMG_0185[1].JPG
    IMG_0185[1].JPG
    2.7 MB · Views: 296
  • IMG_0183[1].JPG
    IMG_0183[1].JPG
    1.8 MB · Views: 284
  • IMG_0181[1].JPG
    IMG_0181[1].JPG
    2.1 MB · Views: 295
  • IMG_0179[1].JPG
    IMG_0179[1].JPG
    2.1 MB · Views: 297

doc_rot

Oh the usual... I bowl, I drive around...
DTT SUPPORTER
DTT BOTM WINNER
I just had a go at porting my KZ750 head under the guidance of my good friend who has ported lots of heads on both cars and motorycles. his words of wisdom and suggestions (for a mild street motor) were something along the lines of "the big thing is to smooth out the transition from the port to valve seat. On most older Japanese heads I have seen there is a sharp ridge here where the valve seat was machined. You just want to radius this portion slightly. If you remove too much it will lower gas velocity, so you just want to smooth out the transition a little."

this ridge was VERY pronounced on my KZ, almost a 90 degree bend with a sharp ridge. I used a small carbide burr to remove material followed up by "beehive" sander on a die grinder to blend everything out, the most important thing is to have complete control over the die grinder. Use both hands and make sure the head is fixed in some way. work all the way up to the 60 degree cut on the valve seat. Took about an hour. I removed very little material but the internal shape is much smoother. I then sent it out for a 3 angle valve job.

i made this crude drawing to show what i mean.
 

Attachments

  • porting.jpg
    porting.jpg
    715.2 KB · Views: 302

DTT Bike Of The Month Gallery

DTT Light or Dark

www.jadusmotorcycleparts.com
www.cognitomoto.com
https://www.townmoto.com
www.speedmotoco.com
www.lostapostle.ca/
www.sparckmoto.com
Top Bottom