Fish's 1992 750C Engine Rebuild and Other Goodies

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Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Fishrider » 26 Aug 2018, 07:29

Some of you have been following my trials and tribulations in the mechanical section with my 750. Here is a quick breakdown:
  • Bought 750 that was supposedly garaged for 9 years with an odometer reading of just over 3K (not likely but the bike was in good condition).
  • I was told the bike had been dropped at least once.
  • Between myself and a local garage I did the following over about 4 ½ months: Carb job, Tank clean, New Tank cap, New petcock, New tires, Fork seals, Replaced a lot of rubber parts, Overhauled back break caliper (Have parts for front brake calipers), New Battery, Garage supposedly checked over bike.
  • Rode 30 miles
  • Front sprocket was dust (literally)
  • New Front and rear sprocket and chain
  • THEN, figured out that clutch shifter holder was broken off the crank case (most likely from the previous drop).
  • Attempted weld: Failed
So, here I am. Instead of parting the bike out, I decided to do a rebuild, and since I can’t do anything halfway, I decided to go full throttle. My first purchase was a 1984 gpz750 crankcase which I am now waiting on, but I plan to explore the following:
  • 810cc Kit
  • Elusive 6th Gear
  • Other Engine modifications that may be worthwhile (oil pump, clutch, carburetor, etc.)
  • New Paint and other possible aesthetic modifications.
  • New shocks or rebuild shocks
  • Other surprises and possibilities, but I am open to different ideas and paths where they may lead.

I used to own a 550 back in the late 90's early 00's and fell in love with this bike. A whole other story.

I hope to document as much as I can, to hopefully, help others, and get help when needed. I am no mechanic by a long shot, but I have just enough mechanical experience to be dangerous (honestly, most of this stuff, I research endlessly before attempting). I am busy guy with a busy life so be patient. I will update when I can. I hope to do much of this over this next Colorado winter with the help of my 14 year old son, but I am not going to set a time line. I appreciate all the help and input I have already received from the knowledgeable people in this forum. I look forward to, what I hope, is a fun and fruitful build. A picture is always good, so below is the current state.
Attachments
Before Build 1 Small.jpg
Before Build 8/26/2018
Last edited by Fishrider on 22 Sep 2018, 01:46, edited 1 time in total.
Fishrider
 
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Re: Fish's 1991 750C Engine Rebuild and Other Goodies

Postby Fishrider » 30 Aug 2018, 23:32

Got into this a bit this week. Took the engine out. Did it by myself with a floor jack and re-positioning jack stands I moved the engine. Then when the engine was teetering on the frame I had my wife help by moving the jack to the other side. Not easy, but it is out.
2018-08-26 19.16.45-3.jpg

2018-08-26 19.21.40.jpg

I confirmed that the 84 gpz750 engine is a direct fit into this frame. I mocked it up with a couple bolts. So far so good.
2018-08-30 15.06.44.jpg

I messed around with some Zephyr 550 gears I picked up on Ebay. They fit perfectly. The input shaft is indeed short as Daftrusty pointed out in his write up. However, the output shaft is perfect. I don't think i need any modifications there. I have had trouble cycling through the gears. Something to do with the neutral bb's in the 6th gear pinion. The 6th gear won't move over properly after 2nd gear. I got it to go once or twice. Not sure if just needs to be spinning properly, or I don't have everything set quite right.

Newbie screw up of the week. Make sure you find every bolt int the crank case before trying to take it apart. That cost me a solid hour of sweat and tears. One bolt hiding in the corner of the bottom inside where the sump was. Good thing I wasn't planning on saving this case. Also, one of the long bolts did shear off while unscrewing it. If I was being careful and cared about this case I would have done it right, but I was being impatient. Lesson number 1.
Last edited by Fishrider on 30 Aug 2018, 23:38, edited 1 time in total.
Fishrider
 
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Re: Fish's 1991 750C Engine Rebuild and Other Goodies

Postby Fishrider » 30 Aug 2018, 23:36

I guess you can only post 3 pics in one post. Here is a pic of the 550 gears in the old case.
2018-08-30 15.07.03.jpg
Fishrider
 
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Re: Fish's 1991 750C Engine Rebuild and Other Goodies

Postby Swampy » 01 Sep 2018, 16:00

It's all looking good there Fishrider, I love the bit with getting the wife helping out, the sort of thing that I would have her do as well :o keep us up to date with the works please :D
Swamps :)
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Re: Fish's 1991 750C Engine Rebuild and Other Goodies

Postby Fishrider » 07 Sep 2018, 05:23

Thanks Swampy! I have been cleaning up a few pieces while waiting for my Wiseco K810 in. I will take the cylinder head and clutch basket to the machinist as soon as it gets here. I was working on a little 3D print project designing a fender eliminator specifically for this bike. It uses all the grommets some screws and will fit the tail light and even the plate bracket. I didn't like the $90-$150 kits out there, and I have a printer so why not. I have to make and print the long stand off that is missing from the inside of my left engine cover anyway. That will be far easier. I should have a first print in about 24 hours. Its always fun to see where I screwed up in the measurements and such.
Bottom Eliminator.jpg
Bottom Piece

Top Eliminator.jpg
Tail light Top Piece
Fishrider
 
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Fishrider » 22 Sep 2018, 02:15

I have not been able to get much done. In pulling all the little pieces parts off the old crankcase and new crankcase I ran into some trouble. The GPz crankcase had a plug where the oil switch is for the Zephyr. That plug did not want to come out. I carefully heated and tapped and heated and tapped and put as much pressure with my 5mm allen wrench as I could. I ordered a 5mm impact socket for my impact wrench as my set only went down to 6mm. When I received the socket I set about instantly disintegrating the walls of the plug. So I drilled it out a little more and banged a 6mm impact socket in the plug (the one I already had). After a couple more tries I eventually got the plug to come out, and somehow I didn't damage the threads. Now I have everything off the crank case. I am going to take the crankcase and some other bits to be blasted as I am going to repaint the crankcase and the cylinder head even though they are in pretty good condition. Plus I was having the darnedest time getting pieces of the gasket off the case and head. I tried everything, and gave up. So blasting it is. I am going to paint the engine mostly black I think. It is going to be cheaper and easier to let the professionals blast the parts. I researched the heck out of blasting, and decided I just don't have the space or inclination to set up my own blasting system for just a few parts. I hope to get the parts blasted next week. When I get them back I will send the the cylinders off to get bored and honed, and then I have to decide whether I want to paint myself or delegate that as well. I am also deciding on whether to paint the swing arm, but I can always do that later.

In the mean time I pulled apart my clutch hub and ordered dampers from Steve. What a great service he has. I ordered a bit and tap and should have that back together this weekend.

I finished my fender eliminator. Pictures supplied. I suppose if anyone is interested I can print one for you for a small fee. ;)

Eliminator 3.jpg

Eliminator 2.jpg

Eliminator 1.jpg
Fishrider
 
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Fishrider » 23 Sep 2018, 01:45

Ran into and issue with the screws I chose for the clutch hub. They are meant to be counter sunk which is what I planned. However, I estimated that I would have to counter sink them down about 3.5mm which would sink the screws into the dampers. So I have to go with button heads and cut them down. Unfortunately, I keep having to order more and more screws because each time I get something its either wrong or I need something else. Now I have tons of screws I may not ever use. :roll:

Also, I had really tough time getting the rivets out of the hub. I had to overdrill the holes slightly which left me with no choice but to tap for an 8mm screw instead of 6mm. Although, so far that has not been an issue. I used my drill press and hand turned the tap while I kept raising the shelf with the crank to keep pressure between the tap and the hub. Worked rather well.

Screw Clutch Hub.jpg


Clutch Hub Counter Sink.jpg


Tapping.jpg
Fishrider
 
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Fishrider » 16 Oct 2018, 20:48

I have been sitting on this project, slowly getting some things done in the background. I got all my engine parts back from blasting. They look great. I need to get them painted, but before I do that I thought I would ask the forum a very important question before I move on. I purchased the Wiseco k810 psiton kit and planned on having the cylinders bored and honed. However, I was also researching getting the head milled about .020" to gain compression. I am not attempting to build a racer here, but I like having a bike with decent throttle response. Since the engine is in pieces I figured I should research milling. I know that I will have to slot the cam sprockets and degree the cams if I do this.

My questions are: Is there anyone here who has had experience with milling (decking) the cylinder head? Will I be able to get away with just a little higher octane at the pump, or will I even need that? Will I need the higher octane for just the Wiseco 10.25:1 compression. Is it even worth milling the head at all considering the added time and expense of slotting the cam sprockets and degreeing the cams. AND I assume I will need to rejet, and I don't want to make a mistake there either. I don't want to drill and ruin my carbs with a Dynojet kit if that is not needed. Can I just try different needles and go from there. A lot, I know, but all of my research leads to more questions than straight answers as I have no prior experience, and I have no wrench friends to ask. I may not even be asking all the right questions. Anybody with some of this specific knowledge? TIA
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Re: Fish's 1992 750C Engine Rebuild and Other Goodies

Postby Freddy » 17 Oct 2018, 03:35

Will I need the higher octane for just the Wiseco 10.25:1 compression. IMO Yes, 95 RON would be my recommendation

Is it even worth milling the head at all considering the added time and expense of slotting the cam sprockets and degreeing the cams. IMO, No, not unless it is warped and then only enough to make it flat. The bigger bore will increase compression significantly. As you say your're not trying to build a race winning bike. You are correct that your would need to degree the cams if you shave the head. Let me know if you find a reliable source of what the stock cams should be set to, I've never been able to find one.

AND I assume I will need to rejet, Yes, but not because of the bigger bore. The engine will suck more air but the carbies will just dispense more fuel based upon this volume of air. The problem is going to be the higher compression ratio will generate more heat. You'll need to pump a richer AFR into the engine to cool it.

I don't want to drill and ruin my carbs with a Dynojet kit if that is not needed. Can I just try different needles and go from there. IMO don't go near a dynojet kit. Stick with genuine Keihin jets. You won't be able to find needles or needle jets, but pilot and main jets in all sizes are readily available. If you were to measure the existing needles and needle jets your would probably find they are worn so are running richer already than when the bike was new. Between playing with pilot jet size, air screw adjustment, fuel height, and main jet sizes I believe you should be able to get the AFR you need. Don't expect it to be easy, there is no simple method. Even a dyno is just a tool to help speed up the process, it still is trial and error on the road .

My tip to speed up finding the right main jet size ..... check out what sizes are currently fitted to the bike. Expect the center carbies to be one size larger than the outside ones. You'll need a magnifying glass to be able to read the jet size stamped on them. Genuine jets number start with a something like a 'star of David' symbol. Whatever size the inner carbies are using, start by fitting genuine jets one size bigger than this inner size to all 4 carbies. Just to clarify, that will make it one size bigger in the middle carbies, and two sizes bigger on the outers.

Genuine Keihin main jets purchased from 3rd party suppliers are very cheap, something like about $6 each


http://www.pjmotorsports.com/keihin-jets.html
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