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Author Topic: I stepped in it - XS750/896 build  (Read 4177 times)

Offline Frenchtom

  • Posts: 19
I stepped in it - XS750/896 build
« on: Jan 25, 2018, 19:03:53 »
Well - I finally pulled the trigger after months (years?) of lurking here and other sites.  Found a 1977 XS750 that came with 2 XS850 engines and the nice standard tank, not the teardrop style.  The engine in the bike supposedly runs, the one on the floor does not but seems like it would with only some select parts added back.  What you cannot see are the three or four storage bins full of parts behind where I was standing when taking the picture.  The PO chopped the frame which made getting a title a 4 month affair.  Just got it this week after buying the bike in September and now its titled as a 2017 custom.  Kinda weird but oh well.  My plans are a cafe racer style with more emphasis on the racer part and less so on the cafe part.  Other details:

Convert the engine to an 896 big bore
Maybe do a cam upgrade
Weld on a hoop and fab a nice teardrop rear fender
Fab a seat
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.
No pods!
Powder coat the frame and other select components
Relocate the upper rear shock mounts to a more forward leaning position
New shocks and front springs, progressive rate
Digital ignition module in place of the points and condenser type
Build a new exhaust system (current pipes are chopped up MAC's and probably not salvageable
Tires, brakes, maybe clutch plates, fix second gear, LED brake and signal lights, etc
Paint, buff, polish, the works.

I live about 1.5 hours from Virginia International Raceway and have a stretch goal of running in an old fart's division where passing happens only on the straights and everyone values their real job.

The first advice I would like to ask for is what kind of welding system should I get for the exhaust fab and the shock mount relocation?  I have single phase 110, and 220 access and no experience whatsoever.

Thanks,
Frenchtom
1963 Honda Sport Cub
1977 Yamaha XS896

Billet: about as creative as duct tape

Offline Frenchtom

  • Posts: 19
Re: I stepped in it - XS750/896 build
« Reply #1 on: Jan 28, 2018, 12:14:52 »
Well - I spent an hour going through 3 bins of parts and I am pretty sure that I have everything but it is all covered in grease and oil.  I found a bunch of '73 Monte Carlo parts from the PO's project car and a bunch of extra XS parts that I will have no use for.  The headers that came with the bike appear to be a MAC system that was modified by an angry beaver. 

I ordered the 896 piston kit last night and have a co-worker lined up who can bore out the cylinders which I will pull off later today.  I am pretty sure the 896 kit comes from china so I am going to measure the piston ODs and grind all the piston down to match the one that is the smallest OD.  I'll probably skim the smallest one also to make sure these things are round and not egg shaped.  Hopefully I do not open up any porosity.  The bike will likely be an 890 CC or smaller when I am done but at least my cylinder walls will be a skoach thicker as a result. 

Also found the three Mikuni carburetors which look a little rough on the outside.  Will open those up ASAP as well and thoroughly cleanse and rebuild.

Frenchtom
« Last Edit: Jan 28, 2018, 12:20:38 by Frenchtom »
1963 Honda Sport Cub
1977 Yamaha XS896

Billet: about as creative as duct tape

Offline Integra99

  • Posts: 95
Re: I stepped in it - XS750/896 build
« Reply #2 on: Jan 29, 2018, 09:55:31 »

Welcome Tom, I love the XS750 having built mine into a cafe racer... she is more cafe than racer though!

If you get hold of an 850 loom from 81 onwards this has electronic ignition and 2,000 miles on and had no issues for me, it has a fairly hefty CDI box but I managed to relocate under the seat.. this was temporary but has been ok.

I had trouble with the old Mikinis so fitted a set of Triumph Daytona carbs which worked really well,

Engine is back out for a rebuild currently and to fit some FZR rear sets so phase 2 of my build. She is a heavy old lump so don't get to excited about racing, a guy nick name JCW however has had some good results.. he is on Caferacer.net .

I used FZR600 forks and R6 Calipers on the front.. stops well. She isnt fast but I have fast bikes so I just love the sound of the triple and large intake carbs. It gets a lot of attention but its shaft drive and does suffer a little with handling .. no idea the effects on this with the rear shock angle changed so you may want to investigate this.. I plan to fit some progressive rear shocks later this year.

You have a lot of work so good luck with it all..  engine is fun to get out!

Heres my baby...

Offline Pete12

  • Posts: 257
Re: I stepped in it - XS750/896 build
« Reply #3 on: Jan 29, 2018, 18:06:14 »


I ordered the 896 piston kit last night and have a co-worker lined up who can bore out the cylinders which I will pull off later today.  I am pretty sure the 896 kit comes from china so I am going to measure the piston ODs and grind all the piston down to match the one that is the smallest OD.  I'll probably skim the smallest one also to make sure these things are round and not egg shaped.

Frenchtom

Not sure if you're aware or not, but pistons, while being round at the top, are oval shaped in the skirt, with the large diameter on the thrust axis and the smaller diameter on the pin axis. Also, as a result of manufacturing tolerances, pistons for the same application can vary in size, so the cylinders should be bored for each individual piston and marked accordingly for reassembly.


Offline XS750AU

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Re: I stepped in it - XS750/896 build
« Reply #4 on: Jan 29, 2018, 20:37:52 »
Quote
Found a 1977 XS750 that came with 2 XS850 engines
The 850 engine and transmission would be the best starting point, as they have CDI, better heads, cams and the transmission does not have the spring loaded coupler.
Most people, myself included have used https://www.ebay.com.au/itm/80-81-YAMAHA-XS850-896cc-BIGBORE-PISTONS-KIT-74-5mm-PISTON-10-XS850BB/172498846803?hash=item2829bb8453:g:V5wAAOSwUKxYhvXr.
Looking forward to seeing another 896 out there.
“Engineering is the art of being approximately right rather than exactly wrong.”

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

Offline Frenchtom

  • Posts: 19
Re: I stepped in it - XS750/896 build
« Reply #5 on: Jan 29, 2018, 20:56:11 »
Hi guys and thanks.  Both the engines I have are 850cc so it looks like I got real lucky there.  For some reason the PO used the triple points ignition system from a 750 in the running 850.  I plan to replace that with a Newtronics digital system. 

I did not know 1977 had hypo-eutectic (sp?) or oval pistons.  Will definitely bore each cylinder to size if that's the case or get the pistons turned by on off-set lathe setup to duplicate the different diameters but with a skilled machinist on the lathe, not some hack.  I do not trust ebay chinese stuff so I am concerned about mismatched diameters from piston to piston or inconsistent diameters along the length of each piston. 

I like the black engine and silver frame on the Integra bike.  I think I will leave my engine unpainted but maybe clear coat it.  For frame color I want to do something other than black but nothing radical like yellow.  I'm thinking a flat charcoal or dark silver but it will be a long time before I must decide.

Tom



1963 Honda Sport Cub
1977 Yamaha XS896

Billet: about as creative as duct tape

Offline XS750AU

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Re: I stepped in it - XS750/896 build
« Reply #6 on: Jan 30, 2018, 03:38:22 »
Quote
I do not trust ebay chinese stuff so I am concerned about mismatched diameters from piston to piston or inconsistent diameters along the length of each piston.
So which pistons are you using?
I was a bit skeptical about the "Cruising Image" pistons, but the experienced machinist who bored out the cylinders said they were better dimensionally than the originals would have been. Technology has vastly improved from the 70's. As you can see in the photo the pistons as measured across the skirts (pistons diameter is different top to bottom and gudgeon to skirt. Bottom skirt is max dimension) were within 0.01mm. If there is any doubt then the machinist should bore to suit the individual pistons!

Quote
I'm thinking a flat charcoal or dark silver
Yep, I have gone with "Gunmetal grey" with a clear coat.
I will be interested to see how you go with the Newtronics ignition and if there are any advantages over the OEM CDI.
« Last Edit: Jan 30, 2018, 03:41:17 by XS750AU »
“Engineering is the art of being approximately right rather than exactly wrong.”

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

Offline Frenchtom

  • Posts: 19
Re: I stepped in it - XS750/896 build
« Reply #7 on: Jan 30, 2018, 07:07:28 »
So which pistons are you using?

I bought 896 pistons off of ebay from Cruzin Image. 
1963 Honda Sport Cub
1977 Yamaha XS896

Billet: about as creative as duct tape

Offline TranceMachineVienna

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  • Posts: 1879
Re: I stepped in it - XS750/896 build
« Reply #8 on: Jan 30, 2018, 08:19:50 »
I´m in Sir!Good luck!

Offline Frenchtom

  • Posts: 19
Re: I stepped in it - XS750/896 build
« Reply #9 on: Feb 04, 2018, 13:33:41 »
I got some more work accomplished.  The first order of business was cleaning the 4 basket of parts that came with the bike, they were all covered in a layer of oily slime.  In the process I found LED lights that the PO looked like he was going to mount under the frame which made me skeptical of other things I would find.....and I was right.  I also took the carbs apart and found the first one to be exceptionally clean and in good shape.  The next two, not so much.  Full of white scale, crud and in the middle carb, a collapsed float.  I noticed that the clip position on the needles were set one groove away from the richest setting likely because of running open pipes and the PO philosophy that more gas = more power. 

Now here is a dumb question - I keep reading that 3 into one exhausts and high quality air filters like K&N require re-jetting the bike.  The thing is, I cannot find any jets on these carburetors.  Is it just the needle adjustment for me?

Then I went to the engine and discovered that when the PO was missing a bolt or gasket he would just keep on assembling without them.  For gaskets he used orange silicone, for the missing bolts, he just left them out and filled the holes with silicone.  Nice!  The bike came with a spare engine so he really has no excuse.

The cam journals were full of rust so now I am thinking the engine sat outside for an extended period of time.  The head looks funny too.  The right exhaust chamber was brownish colored, particularly the exhaust valve.  The middle cylinder was black and the right cylinder was sludged up.  There were also what looked like crankcase breather tube running to the engine but only the right cylinder was connected.  The middle and left were plugged and may explain the lack of sludge.  Two out of 3 exhaust valves failed to seal against paint thinner that I poured into the exhaust port so I think I will lap all six valves for starters and if that does not work I'll cut new seats.  I also have a mental note to check for bent or pitted valve stems and worn out guides. 

I pulled the cylinders and found minor scoring on the front or exhaust port facing wall, same with the pistons.  These will get corrected via the 896 kit. 

I have decided that I am going to pull the crank to check bearing clearances and clean out the case.  I'll also address the second gear issue these bikes have while I am in there. 

Tom

PS - I cannot figure out how to put text directly over or under my pictures.
« Last Edit: Feb 04, 2018, 13:36:17 by Frenchtom »
1963 Honda Sport Cub
1977 Yamaha XS896

Billet: about as creative as duct tape