Author Topic: 1972 CB750 Four K2 -- Rebuilt to NEW OLD STOCK -- PIX ON PAGE 50 (Read 245335 times)

Terry in Australia · « **Reply #275 on:** January 16, 2014, 01:27:03 PM »

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 · « **Reply #276 on:** January 16, 2014, 03:35:06 PM »

Quote from: Terry in Australia on January 16, 2014, 01:27:03 PM

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.

Terry in Australia · « **Reply #277 on:** January 16, 2014, 05:22:51 PM »

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 · « **Reply #278 on:** January 16, 2014, 05:26:41 PM »

Quote from: Terry in Australia on January 16, 2014, 05:22:51 PM

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 · « **Reply #279 on:** January 16, 2014, 05:30:26 PM »

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 · « **Reply #280 on:** January 16, 2014, 06:03:15 PM »

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 · « **Reply #281 on:** January 16, 2014, 06:48:00 PM »

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 · « **Reply #282 on:** January 16, 2014, 06:55:38 PM »

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 · « **Reply #283 on:** January 16, 2014, 09:57:00 PM »

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 · « **Reply #284 on:** January 16, 2014, 10:06:10 PM »

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 · « **Reply #285 on:** January 16, 2014, 10:32:08 PM »

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 · « **Reply #286 on:** January 16, 2014, 10:33:26 PM »

Quote from: edwardmorris on January 16, 2014, 10:06:10 PM

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 · « **Reply #287 on:** January 19, 2014, 05:25:39 PM »

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 · « **Reply #288 on:** January 19, 2014, 05:33:29 PM »

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 · « **Reply #289 on:** January 21, 2014, 04:15:37 PM »

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?

RRRToolSolutions · « **Reply #290 on:** January 21, 2014, 05:43:43 PM »

Ed, I've got a friend that has ordered from Yamiya and the experience and quality was "Great" according to him.

Just as an FYI -

Gordon

seanbarney41 · « **Reply #291 on:** January 21, 2014, 06:34:48 PM »

I would be really worried about that shop doing any machine work on your stuff. Think about it. These motors are NOT small block chevy's. Piston to bore clearance is extremely critical with these engines. They already said they don't want to work on mc stuff. Seriously, if there is no one local, just send it out somewhere. USPS is not gonna cost you that much more.

edwardmorris · « **Reply #292 on:** January 21, 2014, 07:21:38 PM »

Thanks Gordon, good to know.

Sean, the shop is a pretty reputed one and are known in the local old car resto enthusiast groups. I know cars are a different story but it would be easier for me to do things locally. The shipping is not all that cheap even with USPS, not to mention packaging also costs money. I will leave that as a last resort.

They are apprehensive about small twins/Vs and old British bike heads and such. Not really sure what happened but like Ron suggested, I'm guessing one bad valve job and someone came screaming at them.

The machinist examined the jugs and asked me if I wanted to bore to the next size. When I asked will you do it? He said get me the new pistons first so I know how much to do. I will be asking for help here and compiling an exact set of specs that I can hand him (I'm counting on Mark, Terry, Gordon and others here for help) and say it has to be done this way. Should he have any concerns, I will promptly bring it back home and look into shipping it out.

edwardmorris · « **Reply #293 on:** January 26, 2014, 06:25:31 PM »

Got some time to work on the bike after a looooong time. Got the connecting rods out and the crank is free but I couldn't for the life of me get the rotor off, even with two strap wrenches holding it down. Left it alone for now before I did any damage. Then scraped off as much of the hondabond on the top case, then the remnants of the jugs gasket.

edwardmorris · « **Reply #294 on:** January 26, 2014, 06:32:35 PM »

Also, tried the back to black on the rear fender after sanding it with 2000grit sand paper, looks nice despite the nasty gouges and scratches.

edwardmorris · « **Reply #295 on:** January 27, 2014, 10:43:24 AM »

As I ready the cases for blasting, I realized there is a bearing in the lower crankcase that I need to remove. I was planning on replacing all transmission bearings anyway, preferably with SKFs since I can literally drive down the street and pick them up. There are three special grooved ones that I'm having a hard time explaining to the SKF guys here. I searched around and also checked with Mark and NSKs are the next best bet and they do seem to have the grooved one, but I still do not know the exact numbers ans suffixes to specify when ordering replacements. Anyone have these?

edwardmorris · « **Reply #296 on:** January 27, 2014, 11:09:15 AM »

AND hello search!

http://forums.sohc4.net/index.php?topic=60026.0

2 x HK2520 Needle Rollers
1 x 3206ATN9 Roller Bearing
1 x 6003 Roller Bearing
1 x 6008NR Roller Bearing
1 x 6204 Roller Bearing
1 x 6205 Roller Bearing
1 x 6205NR Roller Bearing
1 x 6304 Roller Bearing
1 x 6304NR Roller Bearing

6304NR being C3 as pointed out by Mark...

I'd like at least one person who's used these to concur before I place the order....

iron_worker · « **Reply #297 on:** January 27, 2014, 11:11:12 AM »

Did you try an impact on rotor? You were using a rotor removal tool right (IE a bolt lol).

Hit the bolt with the impact then wrap the end of it with a hammer. Repeat. Should come off that way. Warming up the rotor would help too.

IW

edwardmorris · « **Reply #298 on:** January 27, 2014, 12:43:45 PM »

Quote from: iron_worker on January 27, 2014, 11:11:12 AM

Did you try an impact on rotor? You were using a rotor removal tool right (IE a bolt lol).

Hit the bolt with the impact then wrap the end of it with a hammer. Repeat. Should come off that way. Warming up the rotor would help too.

IW

Didn't quite get to using the puller, there is a bolt that needs to come out first. Will get back to it....

MCRider · « **Reply #299 on:** January 27, 2014, 12:48:08 PM »

IF it were still on the bike, you'd take a 3+ ft cheater bar to it. After putting it in 5th gear and cranking the rear brake all the way tight.

With the crank on the table top, if you had a big mutha vice you could chuck it up in. Or an electric impact wrench...

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Author Topic: 1972 CB750 Four K2 -- Rebuilt to NEW OLD STOCK -- PIX ON PAGE 50 (Read 245335 times)