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Author Topic: CB750 F0 - My first rebuild  (Read 4859 times)

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Offline Maksimum Hops

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CB750 F0 - My first rebuild
« on: November 28, 2012, 02:02:48 am »
Hey there everyone! Been reading here for a bit and getting priceless information and advice, so I wanted to put up my build thread...and ask way more questions. I dragged this 1975 CB750F with 22k original miles out of a guy's barn. I picked up an incredible itch somewhere (normally a bad thing) to learn to work on motorcycles, and by golly, my '08 SV just will just not break down, so I wanted a project bike. May I just wanted my Engineer-In-Training license  to mean something (even though it's for Civil Engineering, and I don't work in the field right now). Be careful what you ask for, because what a project I got. I am honestly more interested in learning a lot than producing a performance bike or a quick build, although I'd like to invest less than 2-3 thousand in the bike, and would like to be able to ride it at some point. I'd like to do everything I can myself.

(Oh, and I know there will be a question on this... yes, that is a '91 MX-5...painted pink. No, it is not mine. Yes, I have had to drive it before  ???)

So, what's wrong with this poor neglected steed? Well, pretty much everything, so I figured I would start on an engine rebuild of the stuck pistons. I didn't want to litter this post with a dozen progress pictures, so please check out this album for more: dragonie.imgur.com Here is the full list of what I have recognized I need to do.

  • Tank de-rusted, pinhole leak plugged, lined, new cap and locking mechanism installed. If I find a replacement tank, that may be worth a purchase at this point. I'm concerned that after vinegar or electrolysis I may only have some blue paint and a keyhole left.
  • Petcock repair
  • New mirrors, grips, hand controls, cables
  • Replace steering bearings
  • Replace fork seals
  • Assess and clean up or replace rear shocks
  • Brake job front and rear, have cylinders, need new lines, pads
  • Replace seat pan (original is a coat of rust on the bottom of the seat foam, reupholster seat
  • Obtain or create new seat locking mechanism (long story short, broke off a drill bit and an easy out in the old one, just cutting it off the frame tab at this point)
  • Replace exhaust (for rust level see seat pan above)
  • Clean, tighten, true wheels and spokes, get new tires
  • Rebuild carbs (have not opened them up yet to be honest), replace air filter
  • Replace chain
  • Clean up wiring harness, reconnect electrics, new battery, whatever else will rear its head on this front
  • Install and time points
  • Replace gaskets, valve seals, clean and lap valves (top end rebuild depending on results of leak-down test) clean engine internals, replace piston rings, hone cylinders, replace crankshaft bearings.

Three weeks of lots and LOTS of learning, two cans of Liquid Wrench, zero broken fins ;D (alhough I did break off a sparkplug in the head - see album) several ounces of ATF+acetone, and two heat cycles later, I got it stripped to the frame, the pistons loose and removed the cylinders (which look good enough to just need a hone I think) and am getting ready to crank the case. I have a new primary issue:  The crankshaft is VERY hard to rotate, despite the pistons being out. The cam chain isn't stuck, nor are the piston rods stuck in the case. With my limited knowledge I have come to the conclusion that I have a bad journal bearing. In addition, one of the connecting rods does not flip back and forth easily like the others - I assume this means the bearing for that rod also needs replacing.

I would love any advice or comments you all can offer the current action item or on the build in general.

OH!, and here is a fun little item. I bought the bike with the keys lost. (Not stolen - have title) Not a huge deal, got the number off the ignition and was going to order a key, but figured that is going to be one of the last items I truly need. Weeks later, I pulled off the cylinders, and was cleaning up my workbench in preparation of the cracking the cases. Tiny metal clink sound as I move the engine. What? I look around on the bench... and a clean, shiny key, numbers matching my ignition is laying there. Now, you have to realize - the inside of the engine is an oily mess, and the outside is a worse grimy mess.  I only have had the engine sans head and covers on the bench. Where it came from is a mystery to me.
CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline stuartni

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Re: CB750 F0 - My first rebuild
« Reply #1 on: November 28, 2012, 02:47:09 am »
good luck with the build

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CB750 F0 - My first rebuild
« Reply #2 on: November 28, 2012, 12:57:20 pm »
If I can help be I'd be glad to. I have a soft place in my heart for Candy Sapphire Blue 75 750F's. Bought mine new 4/75 and I'm putting the finishing touches on a ~ $15K restore/rebuild of a bike that cost $1800. I can probably provide invaluable assistance on many issues including parts availability considering I picked up unavailable or NOS parts from 9 countries over 4 years. I've taken MANY photos during the process and some of those may help you. I'm anticipating my bike to be 90%+ new. 
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Maksimum Hops

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Re: CB750 F0 - My first rebuild
« Reply #3 on: November 28, 2012, 01:26:49 pm »
Thank you Jerry! I've seen your name come up a lot when searching for F model questions :) I'm sure I'll run into a bunch of head-scratchers on re-assembly. Right now I'm waiting on the rotor puller and clutch hub to arrive, and using the time to clean up valves, frame, and engine exterior. I also need to pick up some micrometers to make sure pistons and cylinder are at spec.

Wish I had known about the parts availability for the bike prior to purchasing - I am keeping my eye out on a parts bike, but that is a slim bet for this model.
CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CB750 F0 - My first rebuild
« Reply #4 on: November 28, 2012, 03:29:23 pm »
Body stuff is non-existent. Engine stuff is pretty available. Everything else in-between. The rest we can make do. Some good aftermarket upgrades like the seats we got Corbin to start up again. I'd think piston specs should be fine unless you found a rust/corrosion issue in the cylinders. Your shocks are likely shot. Good luck on the tank! 1 pinhole means many are PROBABLY lurking and you'll find out when you clean it out. Acid/electrolosis will find them. Be on the lookout for another tank.

•Tank de-rusted, pinhole leak plugged, lined, new cap and locking mechanism installed. If I find a replacement tank, that may be worth a purchase at this point. I'm concerned that after vinegar or electrolysis I may only have some blue paint and a keyhole left. watch for another tank!
•Petcock repair filter available or new petcock available but no real repairs
•New mirrors, grips, hand controls, cables  mirrors, grips and 1 control available new
•Replace steering bearings tapered
•Replace fork seals available - use Honda
•Assess and clean up or replace rear shocks they didn't last many miles-your's are well past the reg limit
•Brake job front and rear, have cylinders, need new lines, pads pads avail,rebuild kits avail,only front lines avail
•Replace seat pan (original is a coat of rust on the bottom of the seat foam, reupholster seat real used or Corbin avail
•Obtain or create new seat locking mechanism (long story short, broke off a drill bit and an easy out in the old one, just cutting it off the frame tab at this point) keyed as a set, won't find an original new set but later ones will work
•Replace exhaust (for rust level see seat pan above) a few aftermarket avail
•Clean, tighten, true wheels and spokes, get new tires
•Rebuild carbs (have not opened them up yet to be honest), replace air filter may just need a good cleaning
•Replace chain get a strong tensile str chain and never more
•Clean up wiring harness, reconnect electrics, new battery, whatever else will rear its head on this front see how it does b4 tackling this! AGM battery is worth it and get a Battery Tender
•Install and time points
•Replace gaskets, valve seals, clean and lap valves (top end rebuild depending on results of leak-down test) clean engine internals, replace piston rings, hone cylinders, replace crankshaft bearings. may not need to do all crank bearings- if cond looks good just Plastiguage


« Last Edit: November 28, 2012, 03:40:57 pm by Jerry Rxman Griffin »
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline MRieck

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Re: CB750 F0 - My first rebuild
« Reply #5 on: November 28, 2012, 04:34:17 pm »
If I can help be I'd be glad to. I have a soft place in my heart for Candy Sapphire Blue 75 750F's. Bought mine new 4/75 and I'm putting the finishing touches on a ~ $15K restore/rebuild of a bike that cost $1800. I can probably provide invaluable assistance on many issues including parts availability considering I picked up unavailable or NOS parts from 9 countries over 4 years. I've taken MANY photos during the process and some of those may help you. I'm anticipating my bike to be 90%+ new.
I have been with Jerry and can attest to him having a soft head..I mean "heart" for 75 blue F0's
Owner of the "Million Dollar CB"

Offline MRieck

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Re: CB750 F0 - My first rebuild
« Reply #6 on: November 28, 2012, 04:37:13 pm »
Did you get that broken plug out? They can be a real PITA
Owner of the "Million Dollar CB"

Offline Maksimum Hops

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Re: CB750 F0 - My first rebuild
« Reply #7 on: November 28, 2012, 05:02:06 pm »
Still working on the getting the plug out - I set the head aside after some basic cleaning when I was working on getting the pistons and cylinders separated, but the broken spark has been soaking in Liquid Wrench. It doesn't seem to be possible to drill it from the combustion chamber, so I'm going to break out the remainder of the ceramic on the top side and see if I can make some headway from that direction. Most of the tips I've found on this forum, and others online, are "Good luck, hope you don't break your easy out" so I don't think there is an quick way out of this one.

Thank you for the red glow tips on my list! I'm a little worried to hear that the rear brake lines are not readily available, I hope I can adapt another line. I actually had to cut the rear brake line off as it was damaged at one of the fittings.

Maks
CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CB750 F0 - My first rebuild
« Reply #8 on: November 28, 2012, 06:43:26 pm »
If you find NOS rear lines get me one.  ;)  Same store sells hen's teeth  ;D I looked for 5 years. Aftermarket are available but I only wanted original on the restore so I cleaned mine up and reinstalled. Stainless would be a nice replacement.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Maksimum Hops

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Re: CB750 F0 - My first rebuild
« Reply #9 on: December 07, 2012, 01:12:16 pm »
Alright, cases cracked!

First, these guys were a pain, and had to be drilled out.


Bottom Half:




Journal Bearings. Based on the look and feel, I'm thinking Plastigauge the three on the left, replace two on the right due to scoring either way.


Rod Bearings. Gotta plastigauge these, but by the looks of it I will be replacing the one on the far right. That is also the only pin that doesn't rotate smoothly.


Here's the bad news: What is this little guy? Seems to have broken off in two pieces, larger one was right there in the case. Looks like it's below the camchain? Is this something that can just be sanded down, am I going to be reinstalling it with JB Weld, or getting a new bottom case?  :-\
CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline iron_worker

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Re: CB750 F0 - My first rebuild
« Reply #10 on: December 07, 2012, 01:16:30 pm »
Looks like just the end of a small support rib that snapped off. I don't think JB welding it in would really get you much of the strength back and you'd just be waiting for it to break off again and start making it's way around the engine... not good.

I would say you could probably just leave it and be fine but can you get some more pics from different angles and distances so we can get a better look?

IW

Offline immortal

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Re: CB750 F0 - My first rebuild
« Reply #11 on: December 07, 2012, 01:33:27 pm »
very nice little project, Jerry is a great resource he just gave me some great advise on my F1.

My project was finished only 1400 miles ago...I just blew out a rod bearing. One of the very few parts I did not replace so I'm currently doing the same as you except I replaced all my bearings for rods and crank with the green.  good luck with it!  subscribed
Sometimes...the hard thing and the right thing are the same thing!

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Offline Maksimum Hops

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Re: CB750 F0 - My first rebuild
« Reply #12 on: December 07, 2012, 01:57:51 pm »
Thanks immortal, this forum in general has been an incredibly deep well of knowledge  :D best of luck getting the Pegasus back to flight status!

Iron_worker: I've attached more photos below.

Position of this rib relative to rest of bottom case:


Looking at it with the top case on, right through where the cam chain guide sits. Looks like this thing is definitely immediately below the cam chain.


What it looks like with the missing bit.

CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline Maksimum Hops

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Re: CB750 F0 - My first rebuild
« Reply #13 on: January 01, 2013, 11:32:12 pm »
Alright, holidays are finally done - time to get back to work.

Plastigaged my bearings, and excited to find they are all good! All the journal bearings are at .0015" clearance. Based on the total results I am replacing one pair of rod bearings and two pairs of journal bearings, the ones failing the visual/feel inspection. Ordering those now.

I also found and purchased on eBay an original seat and seat pan in good condition, and getting a spare rear cowl with it too.

Also popped out the wheel bearings, and glad I did. They skip and click as they rotate. Getting replacement sets from All Balls, along with their tapered steering set.
CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline iron_worker

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Re: CB750 F0 - My first rebuild
« Reply #14 on: January 02, 2013, 07:54:50 am »
Good find on the wheel bearings. You'd be having a real bad day if your front wheel bearing decided to lock up while riding.

I'd say you're probably fine without that metal rib. Just make sure you've cleaned up any small metal bits left over from the break.

IW

Offline Maksimum Hops

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Re: CB750 F0 - My first rebuild
« Reply #15 on: January 08, 2013, 11:06:29 pm »
Applied micrometers and dial gauge to top end parts and results were not as good. While the cam, pistons are all fine, The exhaust valve guides are not. The intakes have almost no noticeable play in the guides, measurable at or below .001". The exhaust valves on the other hand have play varying from .005 to .015. Need to purchase new guides and valves, and will have to look for a machine shop to install those and cut seats for me. I'll have them helicoil or timesert the spark plug threads on #2 and clean the head anyway while they've got it. Didn't expect for it in the budget. I guess it gives me more time to clean up and paint the frame. Always got more parts to work on!
CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CB750 F0 - My first rebuild
« Reply #16 on: January 09, 2013, 01:00:54 am »
Not surprised that you had a few nasty bearing shells from the nasty dirty look of that lower case! Sorry to hear about the exhausts.

Keep up the good work. Whats tha hell, it's just money  ::) :'( :(
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline Maksimum Hops

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Re: CB750 F0 - My first rebuild
« Reply #17 on: January 13, 2013, 09:06:28 pm »
It looks like all the well priced exhaust valves on the internet at out of stock and Honda wants a hilarious amount for them. Anyone have experience with getting new guides, but keeping the same valves? I would think that would work just fine, since the new guides come oversize and are reamed to correct spec to match valves anyway.
CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline Jerry Rxman Griffin aka MuthaF'er

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Re: CB750 F0 - My first rebuild
« Reply #18 on: January 13, 2013, 11:09:56 pm »
Check with MRieck. He has lots of take off head stuff I'd bet.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline cb750cafe1

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Re: CB750 F0 - My first rebuild
« Reply #19 on: March 04, 2013, 01:34:29 pm »
I don't mean to highjack your thread.  But as you are planning a top end rebuild, I figured this question could benefit you as well.  I am in the middle of my first build, specifically the top end rebuild of a 75 cb750F.  I can't seem to find the right piston rings.  I think that the OEM 13011-300-024 rings are the proper ones, but I have found conflicting opinions on this.  Does anyone know which rings I should get and where to buy them?
Sorry if this question does not belong here; this is my first post on this forum. 

Offline iron_worker

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Offline Maksimum Hops

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Re: CB750 F0 - My first rebuild
« Reply #21 on: March 12, 2013, 09:54:38 pm »
There is an "equivalent"part on Z1:  http://www.z1enterprises.com/ItemDetails.aspx?itemDescription=Piston+Rings+CB750+%2871-76%29&item=KL11-5005

By the way, sorry for lack of updates on the thread everyone. Ran out of money for purchasing new parts for a bit. Going to paint the frame soon when the weather improves. Oh, and a I did get a nice shiny tank with much MUCH less rust, so I'm excited for that.
CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline iron_worker

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Re: CB750 F0 - My first rebuild
« Reply #22 on: March 13, 2013, 08:03:31 am »
Tanks with little rust are few and far in between so that is definitely a nice find.

IW

Offline Maksimum Hops

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Re: CB750 F0 - My first rebuild
« Reply #23 on: April 29, 2013, 07:02:46 pm »
No updates in a long time... been making slow, but steady progress. Pretty much every system component has been disassembled and organized in preparation to reassembly/cleaning. Except for the rear wheel rim.

Some pics:

Carbs varied from astonishingly clean to disgusting. All passages have been cleared, one jet broke and was replaced. The inside of the bowls just need a decent clean now. I'll be replacing the bowl gaskets as well.



This was the old tank
 


And here's the better one i found on eBay:



It's got two pinholes on the side. Which is a great improvement, as after some exploring with a wirewheel, I discovered the bottom of the original tank is almost completely rusted out.
Side-by-side:



Frame totally stripped, bearing races removed, etc. I'm waiting to make sure the title transfer goes through before spending the money on the powercoating for it.



Pic of the work area. Right now stripping the red tank of paint with sanding...by hand...brutal.

CB750 F0 - cases split! http://forums.sohc4.net/index.php?topic=115414.0

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Offline Frankensteins Bride

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Re: CB750 F0 - My first rebuild
« Reply #24 on: April 29, 2013, 07:19:48 pm »
Wow those carbs were a mess!  :o

I can't imagine only sanding to remove the paint. OMG that's brutal. Do yourself a favor and get some stripper or something!
Working on: 78 Cb750k
Waiting for arrival: 73 Cb750

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