Topic: CB750 Motor rebuild... for dummies

[legendary]

This thread was inspired by this one: http://forums.sohc4.net/index.php?topic=29193.0

I liked Jacks open attitude: "I can't do this and I want to learn." I have the same attitude. If you want to know, you must first admit that you do not know. I contacted Jack "smack doogle" and we decided to take the leap together and document what we learn on the forum.

Here is our basic premise:

- The 2 least qualified guys on the forum are going to rebuild their motors for your entertainment. We are guinea pigs not experts.
- Any useful information will be provided by others, quoted from references, or gleaned by you: (ie. Wow! He shouldn’t have done that!)
- Do not hesitate to offer advice and guidance that is why we are doing this.
- Ask anything you like: budget, references, parts, tools, and service sources, could you take a picture of ‘X’ , or even “Who’s stupid idea was that?”
- If we can keep it on topic (more or less) it will ultimately help more people. If needed we may have a separate related thread for making fun of us. :-)
- Regardless of what may follow, it is our intention to end up with reliable, running motors. If it goes really badly we will sell the remnants and shop for     replacements through this forum.

Steve

[legendary]

Here is my motor: 1976 CB750F with approx. 25K miles. I have no reason to doubt the PO claim..but I cannot prove it either. The Bike was vandalized and the gauges smashed beyond recognition.

I removed it from the frame on 12/23/07 when we had a nice day near 50 degrees F. As shown, everything is soaked in penetrating oil and I do have a few of the fasteners loose. I haven't snapped any off and I am being cautious.

[jsaab2748]

Ok men, you asked for it..... GET RID of those cheap screw drivers and get a good set. And at the same time, buy an impact driver to break all the frozen screws loose. You'll be glad you did.
Make sure you have access to a good torque wrench when you begin reassembly, too. My .02 worth... Good luck.
P.S. Get a service manual for your model of bike if you haven't already.

[scunny]

+1 on the impact driver and torque wrench
good idea on this thread, I shall look forward to your progress

[mcpuffett]

Hi Guys , i did my first 750 rebuild last winter with the help of this forum, 2 or 3 workshop manuals ,& the internet ,  i bought a rotor puller and the speciael socket for undoing the clutch centre nut & a smaller range torque wrench, take your time and you will be ok  , good luck,  cheers Mick.

[smack doogle]

I'm Jack
 and I don't currently have the pictures of what the engine looks like right now because the guy I borrowed the camera from is an idiot and doesn't know how to email them.    I'll have them posted here tomorrow (I hope).  I'm at the same stage as Steve with the bike stripped, engine on the bench.  I am poor (okay, just cheap) and I am trying to rebuild this engine with minimum mistakes to keep the cost down, not for horse power or anything, just good running, quality Honda engineering on tap.
 I have zip lock bags with a sharpie so everything will be kept together to ease reassembly, going to buy caliper, feeler gauges and torque wrench in the near future. I have the service manual, parts fiche, and just about every website listed on here to buy accessories/goodies.  Steve came up with this great idea and hopefully it all works out.  Please feel free to comment as some of you already have.  My wife will be assisting me with this rebuild (don't worry, it's not cheating, she's just here to slow me down) adding her two cents from time to time (God help us).  Anyway, Steve and I both know this isn't a race.  We are going to work on our bikes when we can and when funds come through.  This will hopefully be a one stop shop for 750 rebuilding when all is finished in 2012.  Okay, I'm shooting for this summer but sooner would be great.   

[seaweb11]

When you head off to the store to get new tools as indicated above..........

Buy a digital camera   You will want the photos later for rebuild at YOUR disposal

Good luck with the projects guys.

[mcpuffett]

yep thats right a picture is better than a thousand words 

[Terry in Australia]

Well done guys, I'm looking forward to seeing your progress! The good thing about the legendary CB750 engine is that it is dead simple to work on, and to bring back to "as new" condition. I've recently (in the last 12 months) built 2 engines, one stocker, and one "competition", and so all I reckon you'll need parts wise for a "rebuild" is the following:

Full gasket set (CycleX, $59.00)
Set of Piston Rings (Rusty Riders $30.00)
Cylinder Hone (buy the tool to fit your cordless drill, around $10.00)
Heavy Duty Tsubaki Cam Chain (Z1 Enterprises $28.00)
OEM cam chain tensioner, wheel, and guide (Z1 Enterprises $61.00) 
Engine seal set ($20.00 from Rusty Riders)
New OEM Primary Chains (Terry Quail, $70.00 per set)
New NGK Spark Plugs ($10.00 from your nearest auto parts store)
New points ($10.00 from Rusty Riders)
Engine Enamel ($10.00 from your nearest auto parts store)

There's probably one or two items that I've forgotten, but as you can see, for around 300 bucks you can do a full "rebuild" that a shop wouldn't do for under 1000 bucks. Spend the other 700 on good quality tools and better quality booze, and give yourselves a pat on the back! Cheers, Terry.

[smack doogle]

Ah, yes.  The digital camera.  Well, when it snowed a few weeks ago here in Mass. I thought it would be a great idea to bring the Nikon D80 out and take pics of the kids sledding.  Well, long story short, Niko D80 feel in big pile of fluffy white stuff.  D80 doesn't work now.  It's at work now so one of my guys can look at it.

[smack doogle]

Well done guys, I'm looking forward to seeing your progress! The good thing about the legendary CB750 engine is that it is dead simple to work on, and to bring back to "as new" condition. I've recently (in the last 12 months) built 2 engines, one stocker, and one "competition", and so all I reckon you'll need parts wise for a "rebuild" is the following:

Full gasket set (CycleX, $59.00)
Set of Piston Rings (Rusty Riders $30.00)
Cylinder Hone (buy the tool to fit your cordless drill, around $10.00)
Heavy Duty Tsubaki Cam Chain (Z1 Enterprises $28.00)
OEM cam chain tensioner, wheel, and guide (Z1 Enterprises $61.00) 
Engine seal set ($20.00 from Rusty Riders)
New OEM Primary Chains (Terry Quail, $70.00 per set)
New NGK Spark Plugs ($10.00 from your nearest auto parts store)
New points ($10.00 from Rusty Riders)
Engine Enamel ($10.00 from your nearest auto parts store)

There's probably one or two items that I've forgotten, but as you can see, for around 300 bucks you can do a full "rebuild" that a shop wouldn't do for under 1000 bucks. Spend the other 700 on good quality tools and better quality booze, and give yourselves a pat on the back! Cheers, Terry.

Great info, thank you for that.  The extra money for good booze, um, I was raised on schlitz so I guess it's time to upgrade to New Castle. 
Sorry for going off topic

[Ilbikes]

Guys, let me repeat one very important tip - Do not try to remove those cylinder studs! It takes heat and breaking one is not a good thing. They have an entirely different thread/clearance than do bolts/nuts elsewhere on the engine and they suffer from corrosion of did-similar metals. If you are so inclined - talk with someone first.

We'll be waiting on the questions - Oh, please ask before breaking 

You won't regret this.

Gordon

[smack doogle]

Ilbikes, thanks for the tip.  I remember reading that on here once.  I will not touch them.

[754]

Before you run out and buy a hone...

Clean cylinder and take it to an engine shop, and get them to measure with a bore guage..if it has any taper, it should probably be bored. If you dont, at least you know your rings will not last forever..

And before you start figuring out what it should cost..see what you have first... nobody has mentioned a valve job yet...


Proceed..

[jevfro]

I'm going to be subscribing to this thread for sure!   I'm just about the same place as you two so the timing is great.  I will try and just "follow along at home"

Before you run out and buy a hone...

Clean cylinder and take it to an engine shop, and get them to measure with a bore guage..if it has any taper, it should probably be bored. If you dont, at least you know your rings will not last forever..

And before you start figuring out what it should cost..see what you have first... nobody has mentioned a valve job yet...


Proceed..

This is the part I fear... I cant afford all of that work at once if it all needs done 

[bryanj]

I'll kick in with the first freebe,(ish) If you cover the shipping from UK (about $5) I will send you a copy of the original Honda 750 manual on CD in PDF format. E-Mail to BLJ@BLJ.org.uk

[bert96]

Guys, let me repeat one very important tip - Do not try to remove those cylinder studs! It takes heat and breaking one is not a good thing. They have an entirely different thread/clearance than do bolts/nuts elsewhere on the engine and they suffer from corrosion of did-similar metals. If you are so inclined - talk with someone first.

We'll be waiting on the questions - Oh, please ask before breaking 

You won't regret this.

Gordon

I'm planning to change my cylinder stud when i will rebuid my engine,what is the right way to remove them?

[eurban]

Removing the cylinder studs?  Penetrating oil and a few heat cycles with a carefully applied torch to start.  Now get a helper.  Double nut the threaded portion of the stud.  This means that you thread one nut on, a second nut on, and then hold the lower nut with a wrench while you tighten the top nut down onto the lower nut. This "locks" the nuts to the stud. Clamp a GOOD PAIR  of vise grips to the same stud about an inch off of the case.  While one person turns the stud at the top with a socket on the nut, second person turns the stud at the bottom with the vise grips.  Avoid bending the stud while you turn.  This method has worked well for me on 2-3 engines.  IMHO if you want a leak proof engine, replacing the stock studs with heavy duty ones is a good move.  Enjoy.

[Ilbikes]

I will quote and repeat what my old friend Charles does - he's worked on aluminum heads for over 30 years and swears he's never broke one.

1) Have two  (yes two) Vise Grips on-hand.
2) Having a person to help is nice, not mandatory, but nice.
3) Heat the upper case in an oven at 350 for 10 minutes - No more, no less. You have to expand the aluminum and not the studs - this is part of why this works (also the expansion rates are different).
4) Immediately set the case face-down on a piece of plywood or lumber to keep from damaging the mating surfaces. - You must work fast before the block cools.
5) Clamp one stud at a time down low with your two Vise Grips using a 180 degree  (opposed) T formation (the lower the better - just don't score or damage the base of the case/cylinder gasket surface with your tools. Work from the outside to the inside to gget the best access.

Note -You want to turn these studs using a "T" set-up. You want to turn from both sides at once - not with just one with a rachet or wrench as this will generate excess side-load. You want 100% of the energy to be applied to "twisting" the stud out of it's threaded encasement.

Now, if you are going to re-use the studs you need to use the triple-nut technique, not the double-nut set-up so you can use opposing boxed-in wrenches to form your T. By having 3 - you can put your wrenches on the top two nuts and get yout "T" motion going.

Now, I know this will draw criticism as over-kill, but I trust a 70 year-old fellow who does this every week and has for 30 years without a failure. I've only done 5 or 6 in my life and I've broken 2 studs. I promise you, you don't want to try drilling and removing a broken stud. Those have to be welded and turned out by a competent machine shop. I've hae a shop try to drill/tap and it left threads that weren't tight fitting - not good for clamping. 

One more thing - NEVER run a tap in the stud case threads! Again, these are a differetn type and measure of tap. There have a tighter tolerance and if you run a tap in the stud holes or if you run the studs in a die - you have ruined the thread fit intended by the manufacturer. These threads require a special set of taps and dies - you and I don't have access to. I learned the hard way and ruined a valuable Kawasaki H2 case years ago.

Gordon

[paulages]

i've used a stud remover in combination with heat and had good luck. i wouldn't use the stud remover alone if planning to reuse the studs (as it does produce uneven load), but if i were going to reuse the studs i wouldn't remove them at all.

[markb]

I second replacing the studs with APE studs.  If you're patient they will come out.  Also, even with a impact driver you will probably round out some of the phillips head screws on the covers.  If that happens no problem.  Use a 6mm drill to drill off the head, the rounded out cross will center the drill.  When you get to the bottom of the screw head it will pop off, then when you remove the cover there's enough off a stud to remove with a vice grips.
Good luck!!

[bert96]

I bought cylinder studs (APE) from cycle exchange.For the "method" of the oven,i don't think my girlfriend will let me do that

I think i'll take the torch

Thanks for your help!

[Johnie]

Great thread you guys started and I will be watching for sure.  A tip I found useful and so will you guys.  You will be using your new impact driver to remove those darn phillips screws from the side engine cases.  Once those are out junk the screws and get some nice hex bolts to replace them.  You can find those on eBay too.  There is a thread I started on this SOHC site that will give you an idea of what to buy.

[Terry in Australia]

Not wanting to turn your excellent idea for a thread into a "How to remove Cylinder Studs" thread, (maybe we should have a separate thread just dedicated to this subject mods?) I've used the "double nut" method with reasonable success on one engine, (K2) but the second engine (K6) must have spent more time in the weather, and there were several studs that weren't gonna give up their grip on my cases easily, so, as I wasn't gonna re-use 'em, I did this:

I bent 'em at right angles, (OEM studs are pretty malleable) poked the end into a 2 foot length of pipe (old handlebars would work fine) and just turned them out. One bend will be enough to "crack" them, then I just straightened them out good enough to get them out then pitch them in the trash can. Mechanical Butchery, I suppose, but it worked fine. If I was gonna re-use them, (and I don't know why I'd do that) then I'd use Gordon's method, for sure.

Now back to the original subject, there will be those folk here who will suggest that there might be a need to "do this, or do that" which could add up to a lot of cash, but don't be frightened off by this, these guys are more interested in seeing how you react to their posts, than actually contributing in a positive way. Don't worry about it, if you need a "valve job", we can talk you through the process of lapping in your valves for the price of a can of valve grinding paste and a suction cup. If your valves are buggered, there are enough of us here with spare parts to help you do it cheaply, same goes if your pistons or cylinders are worn out, but we'll help you work through each stage. As GW says, "Stay the course" and the reward will be something that you've done by yourself, and can be proud of. Cheers, Terry.

[legendary]

Guys,
         I am really surprised by the response to this thread....lots of reads and lots of excellent info and I appreciate it!

Like Terry said there will certainly be lots of differing opinions as we go. I know there are more than a few methods of arriving at the goal. When I get to each step of the process I will have to weigh the options. Hopefully I can post enough pictures of my specific motor to reach an appropriate decision.

Oh by the way.... I am getting a lot out of this. If it would benefit someone else to see me take it a bit further than necessary...and the cost/risk is tolerable.... I might take on a few extra procedures.

Here is where I am today:

Bought an impact and had every screw loosened in 20 minutes.... nothing broken.



This is the impact driver I bought at SEARS today $24.99 (US Dollars). If you are opening one of these up I consider this a  must have tool. Remember when this job is done I will still have this, and several other new tools..... and I am saving tons of money on labor.





Motor with every fastener you can see loosened.

Question of the day:  Every visible fastener is out of the cylinder head. What is a good method for breaking it free of the gasket material without doing any damage?

Learnings for today: 1). Put Band-Aids and hand cleaner on your shopping list.
                            2). Before you tear down a bike- drain the oil from the motor if your plans include a tear down.
                                 This is easier when you can reach the drain plug.

Thanks for all your help guys. Good to be off and running.   Steve