1978 YAMAHA XS1100 ENGINE HOP UP

The decision to Hop-up the backup engine was made based on the availability of the Wisco 1179 kit and the condition of the back up engine.

  

 

 I figured that as long as I had 2 engines I was in good shape if something was to happen to ether one of them. I put together a cheap wood stand for the engine and started the disassembly.  

   

At this point I had enough parts including engine covers for both engines.  I checked each part as the engine came apart. The cams and bearing of the back-up engine were pristine, not a scratch on any of the mating surfaces.  The engine only had 34000 miles on it and that’s nothing for these puppies. The head was removed and the first signs of trouble were seen.  The combustion chambers were plugged with about 1/8 of an inch of carbon build up and the head gasket was on the verge of blowing.

 

Before removing the cylinders I took a closer look at the head and valve train. The cams and sprockets were in very good shape but the valves were in need of a cleaning.  

     

 The fit in the guides was nice and snug. Even with all the oil cleaned off the stems and out of the guides no free play what so ever could be felt. The valves also checked out as being perfectly straight.  With the valves confirmed as good I cleaned the head and valves up with a brass wire wheel. Springs were also checked and confirmed as good to go. The head was glass beaded back to the bare metal and sent out to the machine shop to be planed.

  

The gasket surface was corroded and with the time and dollars invested I didn’t want to take any chances on a bad head gasket seal.  I will have to get the  machine shop to remove a few thousands of an inch to get into good solid metal. I decided that I would try my hand at a bit of porting work and did the research.  From what I gathered from many sites and talking to people the average guy could get at least 15 percent more air flow if a careful job was done.  I also was told that there was no sense on porting the intake side unless I owned a flow bench.  The intake boots and intake ports were a near perfect fit to one another so I opted to take that advice and focused my effort on the exhaust ports only.  I acquired a porting and polishing kit and went to work on the head. The work was pretty slow going and I had a far amount of material to remove. After about 3 hours of work I put down the porting kit and went out and got some carbide cutting bits for my high speed moto tool.  WOW this was a real time saver.  It cut the soft head metal so fast that great care had to be used to prevent taking out too much material. After the bulk of the port material was removed I returned to using the porting kit to smooth things out as much as possible.  It took about 16 hours to enlarge the exhaust ports to match the exhaust gaskets.

 

With that job completed I cleaned and polished the combustion chambers and replaced the valves. To confirm a good valve to valve seat seal I turned the head over and filled the chambers to the gasket surface with alcohol. If there were any leaks at the seats alcohol would find them.  All was good so I didn’t lap the valves.

 

 

 

 

Next job was the cylinder removal.  What a job, WOW the base gasket was very well bonded to both surfaces. It took a lot of prying at the pry points and pulling to get the cylinder block free. Prying at the pry points only fattened the gasket up but this did allow me to get at it with a razor blade knife.  I worked at it carefully with the knife and was spraying gasket remover into any opening that I could create. Getting the cylinder block free took several hours to do without damage.  

 

 Off to the machine shop for the boring work.  There was only one shop in town that kept coming up when I was asking around about who could do the work so I went with that shop. They did a perfect job.  I had numbered the pistons and cylinders before dropping the parts off so they matched things up as compared to just boring it out to one size across the board.

 

 They also planned the top surface of the head to a like new condition.

  

I checked the Wisco rings to each cylinder at three locations per hole and made the adjustments as necessary. With the head, cylinder block, pistons and rings ready to go it was time to check the transmission and other bottom end parts.  Checking out the bottom end involved splitting the cases for access and that job went pretty smooth. Once the cases were apart I saw that the bottom end appeared to also be in very good shape. Again there were no scratches on the crank bearing surfaces or the crank.    

 

 This was in spite of what looked like a lot of debris in the lower crankcase. The Known transmission 2nd gear issue was corrected the easy way by changing the location of the second gear spacer washer on the shaft. This is a know easy fix for the trany of these bikes. The gears were in great shape so I opted to not get into undercutting and modifying them.

 

 With the bottom end and trany looking good I cleaned everything up and put the cases back together. 

  

 

 Note … don’t do this the way I did.  I had failed to remove the stator from the right hand side of the crank when I split the cases and putting the cases back together with it in place was impossible.  I ended up having to remove it to do that part of this rebuild. removing it with the crank not pinned in place by the mated cases it a more difficult job to say the least. The clutch was a different story compared to the rest of this engine.  All the discs, both types, were burnt.  I didn’t have any new plates in fibre or steel so I cleaned up what I had just to complete the job and get the engine sealed.  The clutch will be re-addressed this spring with new plates. I already have them. So with the cases back together and the side covers back on the engine it was time to install the cylinder block and head.  

 

 I think the most difficult part of the entire job was getting the cylinder block down over the piston rings without braking any of the rings.  Boring out the cylinders almost completely removed the chaffer at the bottom of the bores so getting the rings into the bores was very difficult even with ring compressors. I did however manage to get it done.  If I do this sort of thing again I will make that part a 2 man job for sure. One person lowering the block while the rings are fed into the bores by the other person. Installing the head and checking the timing was easy enough and the engine was soon ready to install in the bike.

 

 The engine re & re took a total of about 4 hours and she fired right up but ran rough. I had also installed a different pipe that sounded much better and breathed better as well.  After a quick tune up the engine was running very smoothly.  There wasn’t even any valve chatter.  I was surprised and pleased.  All was GOOD.  I didn’t do much with the bike in the way of wrist twisting because the rings needed to be seated to the bores and a break in was required.  I drove the bike around for a few weeks waiting for the 500 KM head re-torque mileage to come along. Over this period I kept the RPMs on the change and did a lot of trany shifting.  Everything appeared to be good and the trany was smoother then expected. After doing that break in procedure and head re-torque it was time to see what I had.  On a mid fall Friday evening I took her for a drive around the city and then headed out to the highway.  I’m not sure what it was that told me to give her a good twist but that’s what I did.  From a set of lights on the highway I let her loose.  The bike was not very responsive off the line but when she found 5300 RPM she TOOK OFF rather strongly and without notice. That however proved to be just a tease. When she hit 7K the RPMs literally jumped to past the red line and the bike almost came out from under me. I was instantly moved into the passengers spot on the seat and she was still pulling away. It was an eye opener and because it was unexpected I must admit that it scared me for that instant.  I was sure I was going to go off the back of the bike that evening.  WOW I love biking!!  I now hang on tight and squeeze the bikes body with my legs before twisting the throttle in the 7K range.  This engines attitude is in keeping with what I was told I could expect as a result of the exhaust porting.  Exhaust porting tends to move the power to the top of the RPM range. This can be controlled somewhat by playing around with the exhaust pipes collector pipe length and DIA and I may play with that at a different time.   I am happy with the bikes performance in the 5K and above range but she still needs help in the just above idle to 5K range.  More tuning is required and this job will continue until I get it JUST RIGHT.   

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5 Responses to 1978 YAMAHA XS1100 ENGINE HOP UP

  1. Steve says:

    Thank you this has been the best thing I have read about re-building my 1981 Yamaha XS 1100.

    • Thank you. I’m glad you found it helpful. When this Blog was an MSN spaces blog, before the forced change to Word Press, it was referenced in Motorcycle Classics Magazine as one of 2 sites to go to for information on these bikes .

  2. Its like you read my mind! You seem to know a lot about this, like you
    wrote the book in it or something. I think that you can do with some
    pics to drive the message home a little bit, but instead of that,
    this is excellent blog. A great read. I will definitely be back.

    • The formatting and Pics got messed up when I was forced to make the change from MSN spaces to here. Anywhere where there’s no text, the text can be made visible by highlighting the text area with the mouse.

  3. I love it when individuals come together and share thoughts.
    Great site, stick with it!

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