Topic: 1972 CB750 Four K2 -- Rebuilt to NEW OLD STOCK -- PIX ON PAGE 50

[MCRider]

ordinarily this would be done with a media blaster, like plastic beads or soda. Glass beads but that means heavy duty cleaning protocol.

You're too far along now. Continue.

[edwardmorris]

ordinarily this would be done with a media blaster, like plastic beads or soda. Glass beads but that means heavy duty cleaning protocol.

You're too far along now. Continue.

Drats! I thought soda blasting was baaaaad because crap gets stuck in places? I have a poor mans blaster at home, think I can finish of the rest with it?

Besides, the carbon was so badly caked, I had to quite literally chisel it out first then wire brush it later, so maybe its for the best...

[MCRider]

Soda's not strong enough for the cake on stuff/ Plastic bead blasting would make short work of it. If you had one nearby. Still got cleanup/out issues, but residual shouldn't hurt anything.

Soda is water cleanup so the sink being big enough is the prob. Or good enough weather for a garden hose.

[calj737]

Edward - you could also have the head Hot Tanked at a local shop pretty inexpensively. Soda is not on the phone corrosive not a problem for entering the engine, only the carbs. It can and will clean out pretty easily.

Glass beading, with your head at this stage of disassembly, is also pretty safe. Just need to rinse the head well to insure flushing is complete (same would be true with plastic media, sand, etc). You could soak the head in SeaFoam Deep Creep. It does soften hardened carbon, but will take some time and continued effort. Hot Tank it for best, complete and quickest results.

[edwardmorris]

I will ask the local machine shop to reconsider the motorcycle engine for at last bead blasting. Cleaning those pesky fins will take up too much time. I don't know why they're so fussy about motorcycle engines, this thing is as big as a small car.

If they do agree to blasting things clean, do I finish the valve lapping etc. before or after?

[calj737]

Machine work AFTER blasting, whatever method you choose.

[MCRider]

Machine work AFTER blasting, whatever method you choose.

YEah, they're going to balst the seats, so machine/lap etc afterwards.

They probably had a bad experience with someone's part and did a knee jerk reaction, "no motorcycles". Should be no problem, done all the time.

Edward - you could also have the head Hot Tanked at a local shop pretty inexpensively. Soda is not on the phone corrosive not a problem for entering the engine, only the carbs. It can and will clean out pretty easily.

Glass beading, with your head at this stage of disassembly, is also pretty safe. Just need to rinse the head well to insure flushing is complete (same would be true with plastic media, sand, etc). You could soak the head in SeaFoam Deep Creep. It does soften hardened carbon, but will take some time and continued effort. Hot Tank it for best, complete and quickest results.

Do you have first hand experience with a "hot tank"? I took my parts to a hot tank shop and they turned me down. Said their tank would melt aluminum.  I confirmed this at other shops and the internet.

A solvent tank of a lessor sort may work, but probably not an actual "hot tank".

My pref is plastic bead blasting. 2nd choice is soda.  I actually soda blasted my VM29s (carbs) (in my build thread and services rendered thread) inside and out. Did a great job and cleaned up in water in my utility sink.

[edwardmorris]

Thanks for the info guys! No luck with the shop though, they still adamantly refuse to touch anything motorcycle related. I will see if I can find a shop in the Chicago area (comes with Chicago prices and Crook County taxes as they say out there) that will do the blasting. Last resort would be start heading towards Indy Next few days are brutal work wise, hopefully I'll be able to sneak in an hour or two to get something/anything done.

[edwardmorris]

In between shifts, used the quick hour to clean up the valves. Mostly cleaned up nice (pic 1 and 2 before and after sample), slightly concerned with all the gunk on the seat/sealing area of the valves. Didn't want to go razor crazy on it, will lapping with coarse compound clean this up (pic 3)?

[Terry in Australia]

G'Day Ed, that valve looks like it's past it's use by date mate. The valves can't be ground like some automotive valves according to Honda, so you might need to go thru your spares and find a better one. No amount of lapping will fix that one.

Reference the "Hot Tanking" conversation, I don't know if there's differernt types, but Rex Wolfendon (probably Australia's most knowledgeable CB750 racing guy) told me that he has his engine cases, heads, cylinder blocks etc hot tanked as he doesn't like media blasting as it's a PITA to clean them perfectly afterwards, and considering most cars have aluminum heads nowadays, I can't see why your head can't be "tanked".

The only thing that the hot tanking won't remove apparently is corrosion though, so something to consider if you have your cases done. Cheers, Terry.    

[MCRider]

G'Day Ed, that valve looks like it's past it's use by date mate. The valves can't be ground like some automotive valves according to Honda, so you might need to go thru your spares and find a better one. No amount of lapping will fix that one.

Reference the "Hot Tanking" conversation, I don't know if there's differernt types, but Rex Wolfendon (probably Australia's most knowledgeable CB750 racing guy) told me that he has his engine cases, heads, cylinder blocks etc hot tanked as he doesn't like media blasting as it's a PITA to clean them perfectly afterwards, and considering most cars have aluminum heads nowadays, I can't see why your head can't be "tanked".

The only thing that the hot tanking won't remove apparently is corrosion though, so something to consider if you have your cases done. Cheers, Terry.

Besides my personal experience referenced earlier, a Google search brings up as much consternation on this subject as an oil thread. What I've been able to boil it down to, is that there are degrees of "hot tanks". A good old fashioned hot tank, filled to the brim with very unfriendly to EPA, acids, is the hot tank of yore, capable of melting aluminum in short order, designed primarily to clean cast iron. On the other end of the scale is something barley more than hot soap and water, still called a "hot tank". And everything in between.

OCICBW, but I really searched on the subject. The car guys have mile long threads. Yes, no, maybe so.

[calj737]

My reference above was to the systems in use in the US today, which are, EPA and alloy friendly. They are essentially heated parts washers where the fluid is sprayed in a rotating tub under higher pressure. These appear to do a very capable job of degreasing and removing carbon build ups on engine parts, aluminum included.

[Terry in Australia]

Yeah, and I was watching an English car show called "Wheeler Dealers" where they took a tour thru a factory that repaired alloy wheels.

The wheels were dumped into a "Hot Tank" that was full of heated acid that removed the old paint, powdercoat, etc, in only a few minutes, but didn't harm the aluminum.

Obviously  the technology is there, so you just need to find someone locally who will do it for you. Cheers, Terry.

[MCRider]

Yeah, and I was watching an English car show called "Wheeler Dealers" where they took a tour thru a factory that repaired alloy wheels.

The wheels were dumped into a "Hot Tank" that was full of heated acid that removed the old paint, powdercoat, etc, in only a few minutes, but didn't harm the aluminum.

Obviously  the technology is there, so you just need to find someone locally who will do it for you. Cheers, Terry.

Yes, I'd agree to that. Ask around. Don't like the answer, keep asking. Helps to live somewhere big enough to have choices.

[Terry in Australia]

Ha ha, that's so true Ron, I was born and raised in a small country town, and if you couldn't get something done locally, you'd have to plan a trip to the "Big Smoke". (city) When I had my CZ250 Scrambler, I used to destroy pistons fairly regularly, and it'd take a minimum of two weeks to get a replacement. What a PITA.

[BPellerine]

Mark aka hondaman says that you can have valves ground in his book you might read up on that subject in his book.used to have it done for brit bikes but you cant take a lot off or they will be sharp and burn easily.bill

[edwardmorris]

Thanks guys, in between shifts yet again, I'll make time to read through and see what can be done. The valves from the original head all have some runout, and two are completely useless. If I can't grind this down, then next week will be yet another killer work week, BUT I'll get new valves

So true not finding service providers where you live, what a PITA. There's another thing that's been bugging me lately, I've learnt over and over that rushing this thing is only ending up in damage to time and money, so I should start getting things done once and right the first time. What I'm worried a bit is about those cylinder clearances. They are pretty close to the limit and I don't want to have to redo the engine for at least 30K miles. Should I save up and go for the next piston size or is there enough on the sleeves to get some serious miles on the bike?

[edwardmorris]

Also, my oil pump super kit came in today from Elan, hopefully I'll have most of Sunday free to try and work on it.

[HondaMan]

The valve grinding question: the "margin" on the edges of these valves is supposed to be at least 1.0mm. When new, they range between 2.0 and 1.6mm, depending on the year of the engine. My general practice with them is: I take them to the machine shop and tell them to "grind until they clean up", and then measure the edge margin afterward. It only costs about $3-$5 per valve, and new ones are 4-5 times that much, so it's worth the checkout. If the margin is at least 0.8mm they make a good street valve: if you're going touring then you want at least 1.0mm or more to help them stay cooler. The details of this are seen in the book.

If you're going dragracing, grind them to 0.5mm to reduce weight. they won't be running long enough to overheat anyway.

[edwardmorris]

Good timing I suppose, I did a gentle grind with 500 grit and drill motor to clean them up a little more. Gotta run back to work so not enough time tonight to measure. Looks like there is pitting on the seat/face and pretty much every where despite the fine grind. Thoughts?

I suppose I can have my local car shop send these in claiming they're from a car and maybe the shop will agree?

[Terry in Australia]

I have to admit that I've never tried to grind one Ed, if Honda says "No", then I don't see the point. I did buy an old valve grinding machine a couple of years ago but the collets were too big for Honda valve stems, so I sold it. I guess with the amount of small Jap cars around now that won't be a problem for a modern machine shop though. Cheers, Terry.

[HondaMan]

Good timing I suppose, I did a gentle grind with 500 grit and drill motor to clean them up a little more. Gotta run back to work so not enough time tonight to measure. Looks like there is pitting on the seat/face and pretty much every where despite the fine grind. Thoughts?

I suppose I can have my local car shop send these in claiming they're from a car and maybe the shop will agree?

Sure: they are bigger than the valves found in most 4-valve Toyotas!

[edwardmorris]

Wow, the whole weekend flew by. Hard to turn down work when trying to keep up with this stuff. Anyway, what little time I had left today and the small break yesterday I made some progress. I tried pulling the tires out myself, gave up pretty quickly and thankfully so. The local car shop still owed me a favor so I took the wheels in to get the tires removed. The rims fit perfectly on their machine, but boy did the rubber put up a fight. We got them off eventually and I brought them back and one by one took off all those rotten spokes. Gotta LOVE small size vice grip pliers.

[edwardmorris]

The hubs are a project on their own, especially the rear one. Was so utterly filthy on both sides and a nightmare to clean. A few rounds through the parts washer and some sanding for rust removal, the rear hub looks much better now. I don't even want to think about the polishing part, that's going to be much much worse I bet.

After that, I attempted to correct the second worst mistake on this project (hm341s being the first). I tried left hand bits and extractors starting from the smallest size but the screw didn't budge at all. Eventually I got up to the size of the screw and stopped, convinced that the threads have been completely melded with the screw and there is no way its coming off. Can I re thread and helicoil this drum or should I start hunting down another one?

[edwardmorris]

After much imploring the shop agreed to "take a look" at what I have so I took the cylinders with me (didn't wanna scare them with the head) and said look! inline 4, same as a small car, you can help!. They said yes to bead blasting the cases, fins and a fully stripped down head. They even said they can do a rebore if I needed and that pushed me over the edge. I wasn't sure about using the old pistons again since I'm lacking both the skills as well as tools to properly check the clearances. I think I'm going to go next size up on the pistons now that I know I can get the work done locally. I've been asking around here and almost everybody goes straight for the 836 kit. I've only found that yamiya has all the three oversizes and the random ebay ones pop up here and there. Are there any other sources besides yamiya to get a good set of .25 oversize piston kit?