Topic: CB750K4 what did I get myself into?

[HondaMan]

The Simple Green purple Industrial cleaner available from Home Depot is aluminum safe in concentrations of up to 50% water to S.G.I. and it also does a nice job cleaning in an ultrasonic cleaner. This Aircraft version looks to be cheaper possibly... haven't priced the HD version lately.
Simple Green green formula got banned by DoD as it was found to cause corrosion of aluminum and was affecting composites leading to delamination issues. So, it got banned from base.  They had been using it a lot prior to that ...

David

Good to know, thanks! I had some of that 'tinting' happen to some carbs long ago from the green Simple Green, so I quit using it. It took 24 hours in a carb-soak bath (NAPA Auto solvent) and some soft wire-brush action to remove the dark tint. I'll try the purple next time.

[MRieck]

The Simple Green purple Industrial cleaner available from Home Depot is aluminum safe in concentrations of up to 50% water to S.G.I. and it also does a nice job cleaning in an ultrasonic cleaner. This Aircraft version looks to be cheaper possibly... haven't priced the HD version lately.
Simple Green green formula got banned by DoD as it was found to cause corrosion of aluminum and was affecting composites leading to delamination issues. So, it got banned from base.  They had been using it a lot prior to that ...

David

Good to know, thanks! I had some of that 'tinting' happen to some carbs long ago from the green Simple Green, so I quit using it. It took 24 hours in a carb-soak bath (NAPA Auto solvent) and some soft wire-brush action to remove the dark tint. I'll try the purple next time.

Be very careful with"purple" cleaning products....iyt destroyed a 650 head I had after letting it soak for 24 hours in a 5 gallon bucket. Destroyed the cam saddles.
 The Aircraft Simple Green is awesome. I purposely left some cam cover caps in the solution for 10 days....there was some white oxidation build up BUT it came off under a fine bristle wire wheel. I've tried them all.....just trying to pass on what I've found brothers.

[BrockCB750]

Alright, float bowls, floats and brass small parts are cleaned up. I threw all the brass small parts into a jar wtih some brake clean and just tumbled that around a little to break up the top layers of sludge over everything. Worked well enough. Those got put into the ultra sonic with carb cleaner after.

The float bowls had caked on brown sludge. Scraped off what I could then sprayed brake clean to break up the larger deposits and two runs through the ultrasonic and they look much much better. I think everything probably needs another pass through the ultrasonic though.





The carbs are going well. Still haven't ordered the rebuild kits or anything yet. Want to inspect and see what I actually need. Those floats (not float bowls) looked clean when wet coming out of the ultrasonic but developed that discoloration after they dried. Not sure whats up with that. Any recommendations on if I should replace the floats?

I also stripped a lot more of the bike down and drained the oil. It was VERY dark. But this is the current state of the bike:



Finally, I need to figure out what I am doing with the tank. It actually doesn't seem to have any internal rust. It does have a bunch of built up gunky fuel?

I need to decide how I am going to deal with the dents. Obviously this isn't a situation where I am going to get it perfect and not use filler. Also light exterior rust. I am tempted to just say screw it and use filler over all the dents. Not sure yet. It does need a new gas gap though it looks like. Any recommendations on what to do with this tank is welcome as well.











Getting close to needing to pull the engine out. I actually pulled a muscle (probably while working on the bike a couple weeks ago) and still recovering from that. So might be awhile before I undertake that. Lots still left to do in the meantime. I am anxious to get the frame cleaned up and see whats under the paint and rust.

[RAFster122s]

The Simple Green purple Industrial cleaner available from Home Depot is aluminum safe in concentrations of up to 50% water to S.G.I. and it also does a nice job cleaning in an ultrasonic cleaner. This Aircraft version looks to be cheaper possibly... haven't priced the HD version lately.
Simple Green green formula got banned by DoD as it was found to cause corrosion of aluminum and was affecting composites leading to delamination issues. So, it got banned from base.  They had been using it a lot prior to that ...

David

Good to know, thanks! I had some of that 'tinting' happen to some carbs long ago from the green Simple Green, so I quit using it. It took 24 hours in a carb-soak bath (NAPA Auto solvent) and some soft wire-brush action to remove the dark tint. I'll try the purple next time.

Be very careful with"purple" cleaning products....iyt destroyed a 650 head I had after letting it soak for 24 hours in a 5 gallon bucket. Destroyed the cam saddles.
 The Aircraft Simple Green is awesome. I purposely left some cam cover caps in the solution for 10 days....there was some white oxidation build up BUT it came off under a fine bristle wire wheel. I've tried them all.....just trying to pass on what I've found brothers.

Don't confuse purple cleaning products with the Industrial Simple Green that Home Depot carries that is aluminum safe in concentrations up to 50%. While the purple Industrial Simple Green is purple it is nothing like the other purple cleaners out there...

I agree with you Mike, better to use something aluminum safe like your Aircraft version of the Simple Green!

[HondaMan]

The Simple Green purple Industrial cleaner available from Home Depot is aluminum safe in concentrations of up to 50% water to S.G.I. and it also does a nice job cleaning in an ultrasonic cleaner. This Aircraft version looks to be cheaper possibly... haven't priced the HD version lately.
Simple Green green formula got banned by DoD as it was found to cause corrosion of aluminum and was affecting composites leading to delamination issues. So, it got banned from base.  They had been using it a lot prior to that ...

David

Good to know, thanks! I had some of that 'tinting' happen to some carbs long ago from the green Simple Green, so I quit using it. It took 24 hours in a carb-soak bath (NAPA Auto solvent) and some soft wire-brush action to remove the dark tint. I'll try the purple next time.

Be very careful with"purple" cleaning products....iyt destroyed a 650 head I had after letting it soak for 24 hours in a 5 gallon bucket. Destroyed the cam saddles.
 The Aircraft Simple Green is awesome. I purposely left some cam cover caps in the solution for 10 days....there was some white oxidation build up BUT it came off under a fine bristle wire wheel. I've tried them all.....just trying to pass on what I've found brothers.

Yeow! Thanks for the heads-up. I'll try to find some of the aircraft version.

I can also say that leaving the PD carbs' float bowls in xylene for 2 weeks turns them a dark color, too. Forgot one once, about 6 years ago, and when I came across it again it looked like a deep, dark grey. It's still around here somewhere. It was also far below freezing (mostly 0-10 degrees) in the garage those 2 weeks, I think that may have slowed down the process some. Normally I put them in overnight if they have lots of built-up fuel residue.

[BrockCB750]

Alright lots of progress today. Feels like every fastener is a battle of PB Blaster and heat until I can get everything to break free. Biggest battle this time around was an already stripped screw that I barely got off with the impact before it was completely stripped and the kick starter. So far still only the one broken off fastener on the points cover. Can't believe it.

Here is where it stands today. I think I am offically ready to pull the engine:



Some questions I need a little help with. I am going to take the time to search around the site for answers too but just too exhausted right now after being in the garage in this heat.

1) Carb floats look to be in okay shape. Should I get replacements because these are originals and sat in a field somewhere for 40+ years? Not sure how that the material on the floating part holds up over time and sitting in fuel soaked carbs.

2) Oil tank looks rough. I am fairly certain I need a replacement. Any suggestions where to get a replacement? I am guessing if I want OEM its off to EBAY? I know a few places like Cognito sell aftermarket stuff if I go the custom route.

3) Wiring harness is a mess. Coroded and broken connectors. I see there are replacements but from discussions in this thread about buying parts from some of the usual websites its likely these are of poor quality? Should I reuse connectors that are still good, buy replacement connectors where I need to and make my own?

4) Do I need to pull this bearing to get this stud (for lack of knowing exactly what it is at this moment)? I figured I wanted to remove the long stud in case while pulling the engine if catches on something and bends? Red arrow below:

[denward17]

1-You can test the floats in a small bowl with gas to see what happens.  If you are buying a rebuild kit, go ahead and replace them.
2-How bad does it look? is it rusted through?  (Side note: go ahead and budget new oil hoses).
3-not sure
4-Put the points cover back on if you can to cover it up while taking engine out. (Tape it on if you have to)

[BrockCB750]

Thanks for the advice. I will just get new floats.

The oil tank on second inspection might be slavagable...





The lines look like they are going to be a huge PITA to get off.

[BrockCB750]

Last night while looking for the gray no seize for when I get new stainless bolts I noticed I had some citrus strip.

Tried the citrus strip on a small part of the painted frame and left it over night... the paint came right up! I definitely didn't expect that. Figured I would need something harsher for a frame.

Assuming citrus strip doesn't damage steel or aluminum I know what I am using when I get everything off the frame. The person that left this bike in a field hit it with rattle can black so I will need to strip it off every part of the bike.

[HondaMan]

Last night while looking for the gray no seize for when I get new stainless bolts I noticed I had some citrus strip.

Tried the citrus strip on a small part of the painted frame and left it over night... the paint came right up! I definitely didn't expect that. Figured I would need something harsher for a frame.

Assuming citrus strip doesn't damage steel or aluminum I know what I am using when I get everything off the frame. The person that left this bike in a field hit it with rattle can black so I will need to strip it off every part of the bike.

That oil tank looks like it just needs some paint stripper and new paint. The hoses just unscrew at their nut-fittings, nothing fancy with those fittings except for a soft aluminum sealing washer inside those couplings to seat against the tank's outlets.

The hoses: see if they are still semi-flexible: most are OK. A very few have cracked inner liners, which can flap like a valve and block off the oil flow (on the inner one, closest to the engine when mounted) and cause troubles. The K4/5/6 versions often leak a bit (like a weep) at the crimp on the bottom of the tank, making the fabric covering wet and a very slow drip when oil is hot, tank on the bike. New hoses are pricey, but are good insurance. I'm still trying to make some, need to build some jigs and stuff for it, but been buried with bike engines this summer(!).

About that 'stud' on the crankshaft (under the points cover): don't remove it unless you can first get Honda's specially-made O-ring that goes onto the other end. Normally there is NO reason to remove it, but if you do, it will weep oil with a hot engine unless you replace that special ($5+) O-ring. Normally they are fine, just leave them in place and plan on possibly testing it fro straightness when the whole engine is back together: if it is bent a little it makes the spark timing jump back-and-forth about 5-8 degrees. This shaft should have runout of no more than 0.006", and 0.000" is possible (and desirable) to have.

[BrockCB750]

Just like with everything else on this bike PB Blaster and torch got the lines off the tank. I will likely try to find new lines. Does anyone make good reproductions?

Thanks for the advice on the crankshaft stud. I am going to attemp to pull the engine this weekend which I am both extremely excited for and terrified. Once the engine is out I can actually start the restoration process but the engine is in great shape, fins intact, no other damage other than the fastener that broke off for the points cover.

I am going to use the process detailed in the book, have a wood stand to receive the engine and just take my time. I will have a second person helping me as well.

I do have a question that is probably obvious but I have never pulled an engine off a motorcycle... do I pull the engine while its on the center kickstand?

[newday777]

Kenny Isbery takes apart your old lines, polishes the fittings and puts on new Stainless steel lines.
He's on fb and you can message him. I don't have an email for him....

[newday777]

On the center stand or do the lay over on the right side and lift the frame off the motor.

[Stev-o]

Kenny Isbery takes apart your old lines, polishes the fittings and puts on new Stainless steel lines.

Those look great, did he do yours?

[newday777]

Kenny Isbery takes apart your old lines, polishes the fittings and puts on new Stainless steel lines.

Those look great, did he do yours?

I haven't needed them and I haven't had enough extra $$$ to get a set or 2 made yet for my project bikes so no not yet, but I want some.

[HondaMan]

The sissy bar and fender damage:

This reminds me: I think I have some rear fenders, if you need one?

[70CB750]

Howdy, neighbor.  Where in NoVa are you?  I am near Warrenton.   

[BrockCB750]

@HondaMan thanks for the offer I will keep that in mind. I am still unsure what direction I am going to go with the bike. I will start making some decisions after I get the frame stripped down.

@70CB750 I am in the Centreville area.

[70CB750]

@HondaMan thanks for the offer I will keep that in mind. I am still unsure what direction I am going to go with the bike. I will start making some decisions after I get the frame stripped down.

@70CB750 I am in the Centreville area.

Well, I will see you on the road one day, I am sure.   

[BrockCB750]

Put the paint stripper on the fuel and oil tank. It worked pretty well. Some more wire wheel needed for sure.

Gas tank and oil tank are dented. I don't think I am going to fix the oil tank since you can't see it when its installed. I am not quite sure what to do about the gas tank. Its dented badly where the emblem would go and I very much doubt I will get it back into shape to have the emblem mount correctly. I think I will fill it in smooth and figure it out from there.

[70CB750]

I did it for my tanks.  On Red I filled up emblem spots and smoothed it out.

Tank for the K0 I dropped once  and later on hit a deer - there was a huge dent on the right side. I filled all I could not pull out. 

If you do it, get better filler than Bondo.  I worked in a body shop for a while and the pro filler is easier to work with than what you find in Walmart.

Also after you clean the inside of the tank, check for leaks.  Red's tank leaked from small rusty hole but I was able to solder it and it was good ever since. 

[BrockCB750]

Success! That was a lot more intimidating than it ended up being. Thanks @HondaMan your book did a great job of explaining how to wiggle it and having exactly the perfect height landing spot. I am so happy to have the engine out and undamaged.
 

[HondaMan]

Success! That was a lot more intimidating than it ended up being. Thanks @HondaMan your book did a great job of explaining how to wiggle it and having exactly the perfect height landing spot. I am so happy to have the engine out and undamaged.
 

Wow, your landing deck is MUCH fancier than mine! I use some bricks and a (much-used, now) sheet of oil-blackened plywood. Which reminds me, I have one that needs to come out, too, maybe this weekend?

[BrockCB750]

Started tearing into the engine.

Got the cam out. Didn't realize I had to take the cam chain off so I spent an embarassing amount of time trying to align everything thinking there was some exact perfect rotation of the cam I needed to achieve. Whoops.

The breather cover screw was a huge massive unbelievable PAIN IN THE ASS. Just like your book said Hondaman. My goodness.

Everything in the engine has come out nicely. Sitting 40+ years in oil and not water really goes a long way to making fasteners manageable.





Threw the valve cover back on the engine and called it a day.

Some question I have that I have yet to google myself but thought I would leave out there if anyone has opinions:
1) Are the spacers between the engines fins needed?
2) Where is the best place to buy an engine rebuild kit? I am guessing South Sound Honda and try to buy OEM everything? I prefer to not have to select every single part and just buy a kit.
3) When I go to South Sound Honda to buy parts for some reason when I look up a CB750K4 it has an 'A' after the 4, whats that about?

[denward17]

The small rubber looking spacers are not needed, they are said to reduce vibration noises, or some such issue as that.  I left mine out and I haven't heard any noises.

The parts may depend on what you find when you tear it down further and perform measurements.

You may need to go to an oversize piston/rings.