Author Topic: CB750 Motor rebuild... for dummies (Read 245274 times)

mystic_1 · « **Reply #250 on:** March 15, 2008, 08:26:12 AM »

If your valves and seats are already in good condition and relatively clean, lapping won't produce a huge visible difference. You're going for a uniform satin appearance, with no marks or blemishes on the actual seat angles. You're not wasting your time because the more perfect these surfaces are, the better. Even defects too small to see can cause a problem.

Why not glue the suction cup to the stick with some rubber cement?

mystic_1

Kevin D · « **Reply #251 on:** March 15, 2008, 09:49:10 AM »

Heres my work so far, and the offending tool. I've started on the exhaust valves. The worst of it is so far on #3. Haven't touched #4 yet. I have a 7x magnifier that helps with the inspection. I think I can work the dark spot on #3 out with the compound. There are also some smaller dark spots around the edge of #1. I haven't "micro-inspected" the seats yet but figure them to be OK.
If this was an all out performance build I'd probably be replacing that #3, or sending the head out for a proper job.

Terry in Australia · « **Reply #252 on:** March 18, 2008, 04:27:54 AM »

They look good to me mate, but I'm such a lazy bugger, all I do is invert the head with the spark plug installed, pour some gas (or any other liquid) into the chambers and if none leaks past the valves, they're good enough for me, ha ha!

Quote from: paulages on March 11, 2008, 01:53:16 PM

does you valve cover gasket fit?

G'Day Paul, it took a little effort, but once I got it over the dowels and poked all the screws through the holes, it went on fine. Cheers, Terry.

rugger81 · « **Reply #253 on:** March 18, 2008, 05:58:09 AM »

Quote from: RxmanGriff on March 10, 2008, 07:44:09 AM

Let's get Terry to chime in on the CycleX kit. His is a recent purchase. I thought they were doing their "own" now and didn't think it was Emgo. I guess someone has to make it for them. It's supposed to contain a sooper dooper upgraded head gasket. I know Cometic will make the head gasket and base gasket. Perhaps they could do the others as well.

Rugger - do you have the part number for the top end kit?

Check out this link for bottom end kit B 06111-300-020 http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&viewitem=&item=200204006486

I know I'm a bit late on this, but here's the part numbers I used, both pulled from cmsnl.com. These were for the 77 750K.

a: 06110-393-S00
b: 06111-392-000

Kevin D · « **Reply #254 on:** March 20, 2008, 06:48:54 AM »

I gotta choose one of these head gaskets. To tell you the truth, I think the Vesrah (top) looks better than the Honda (bottom). The cylinder holes are cut to a truer circle and the studs holes are cut a little larger to allow for an oring - which I dont yet have. The Honda gasket (12251-300-307) is coated with - graphite?? - giving it the silvery look.
I'm also working to get the right orings for the oil pressure passages. The orange one was in the vesrah kit, the middle one was what I removed, the lower one is what the partfiche called out (11x2.5). Neither of the new ones has the cylindrical shape of the old one.

Terry in Australia · « **Reply #255 on:** March 20, 2008, 03:42:07 PM »

Yeah I've always wondered about the reason for Honda not cutting "true" round holes for their head gaskets, I've got a few NOS ones I bought years ago, I've used one and it worked fine, but it does look strange when you lay it over the cylinders and you see that it's so "out of round". Anyone know why? Cheers, Terry.

paulages · « **Reply #256 on:** March 20, 2008, 05:47:22 PM »

Quote from: Terry in Australia on March 20, 2008, 03:42:07 PM

Yeah I've always wondered about the reason for Honda not cutting "true" round holes for their head gaskets, I've got a few NOS ones I bought years ago, I've used one and it worked fine, but it does look strange when you lay it over the cylinders and you see that it's so "out of round". Anyone know why? Cheers, Terry.

my bet's on hondman...

HondaMan · « **Reply #257 on:** March 21, 2008, 07:47:57 PM »

Well, my answer there comes from FelPro, not Honda...
Auto head gasket holes look oval, too. It always appear that they are round when you remove them, years later, though. I've done this with several engines (390 V8, 200 CID I6, 351W, a couple of Toyotas...), and they were all the same, started oval or egg-shaped, ended up round. Not perfectly round, but a lot more round than when I laid them on the heads. The interesting part is the steel head gaskets on the 200 I-6, which I have been inside about 4 times, now: those steel ones go on oval and come off EXACTLY round.

FelPro says the oval holes will spread to a round shape when torqued and pressured. It's a short sentence, but that's what they say.

Terry in Australia · « **Reply #258 on:** March 22, 2008, 03:06:33 AM »

That's bloody amazing Mark! Thanks for that!

adpage · « **Reply #259 on:** March 25, 2008, 03:19:28 PM »

Hey guys...great post as I am currently re-building my 1974 CB750 K4. One question about gaskets.....do you use any type of Honda bond or sealer with the gaskets? Or would you install them dry? Keep up the good work!!

mystic_1 · « **Reply #260 on:** March 25, 2008, 03:26:41 PM »

Use Hondabond or equivalent between the crankcase halves, all other gaskets are installed dry. That said, there are various mechanics who coat their gaskets with gaskacinch or use other similar tricks, but I've never done so.

mystic_1

Contact · « **Reply #261 on:** April 04, 2008, 07:06:27 PM »

Hi all I have a question about head gaskets and this looks like the right place to ask. I need to replace my pistons in a '71 CB750 and I don't necessarily want to go with a 836 or bigger kit. If i was to replace them with .25 oversized pistons what head gasket could i use?

754 · « **Reply #262 on:** April 04, 2008, 07:40:14 PM »

stock

Kevin D · « **Reply #263 on:** April 07, 2008, 04:02:38 PM »

I've been working tooooo much lately and not on the CB. 70F today, best day of the year, should be riding but I'm not ready to ride, only to put the cases back together.

I found a gasket cutter and knocked the HG stud holes out to 5/8". I have -014 viton o-rings on the way. I think I'll use the Vesrah HG (the black one). Jonesy helped me with the square section pressure passage orings - thanks Dan.

Also I have the new primary chains fitted - thanks Quail - and the endless HD Tsubaki camchain from Z1. I found this bearing mount Locktite in my fridge, think I'll use it on the trans bearing mounts.

Is there a question here?? I dunno - feel free to criticize if I'm screwing up.

roadkill savior · « **Reply #264 on:** April 20, 2008, 05:43:37 PM »

This has been a very interesting topic as I am also in the middle of a rebuild. I have everything stripped down and parts ordered. My question is this..........when installing the new heavy duty studs and other bolts what should I use on the threads? I'm wondering about the dissimilar metals causing problems. Should I use anti-seize or lock tite? Or am I worried over nothing?

mystic_1 · « **Reply #265 on:** April 20, 2008, 07:43:05 PM »

Quote from: roadkill on April 20, 2008, 05:43:37 PM

when installing the new heavy duty studs and other bolts what should I use on the threads?

If you have these...

... then do this:

mystic_1

roadkill savior · « **Reply #266 on:** April 20, 2008, 08:58:37 PM »

AHHHHHHH I don't have mine yet.....they are coming from cycle exchange...........I'm surprised they have instructions most things with these old bikes don't come with that.

Ok another question..... what if I use stainless bolts to put the cases back together? Stainless and aluminum?

Terry in Australia · « **Reply #267 on:** April 21, 2008, 04:35:45 AM »

No problem mate, I've used stainless "allen" screw kits on my engines, and normally just put them in "dry", but if you want, use a dab of "anti-sieze" compound. Cheers, Terry.

paulages · « **Reply #268 on:** April 21, 2008, 11:57:24 PM »

Quote from: Terry in Australia on April 21, 2008, 04:35:45 AM

No problem mate, I've used stainless "allen" screw kits on my engines, and normally just put them in "dry", but if you want, use a dab of "anti-sieze" compound. Cheers, Terry.

i think he's referring to the possibility of galvanic corrosion from the contact of two particularly antagonistic metals. the stock fasteners are plated, which is supposed to resist corrosion. i've used SS fasteners with no apparent corrosion, but i haven't personally given a real test of time. i try to go with plated fasteners myself.

Terry in Australia · « **Reply #269 on:** April 22, 2008, 01:01:05 AM »

Quote from: paulages on April 21, 2008, 11:57:24 PM

Quote from: Terry in Australia on April 21, 2008, 04:35:45 AM
No problem mate, I've used stainless "allen" screw kits on my engines, and normally just put them in "dry", but if you want, use a dab of "anti-sieze" compound. Cheers, Terry.

i think he's referring to the possibility of galvanic corrosion from the contact of two particularly antagonistic metals. the stock fasteners are plated, which is supposed to resist corrosion. i've used SS fasteners with no apparent corrosion, but i haven't personally given a real test of time. i try to go with plated fasteners myself.

Yeah, I understood Paul, GS Suzuki's had a real problem with busted exhaust bolts due to "galvanic corrosion". The fix then, and now,was to use stainless fasteners.

Don't ever use unplated steel bolts though, some guys used "unbrako's" and they only lasted a few months before they were buggered. Cheers, Terry.

City Boy · « **Reply #270 on:** April 22, 2008, 04:12:08 AM »

I have used some unbrako fasteners in the past.I had them all yellow iridite plated before use and was pleased with the results.Cheap process too. Rock On

Terry in Australia · « **Reply #271 on:** April 23, 2008, 01:16:58 AM »

That's it mate, get 'em plated and they're fine, but don't use 'em "raw", or you'll regret it!

SandwichEnthusiast · « **Reply #272 on:** April 25, 2008, 04:24:44 PM »

Quote

Don't ever use unplated steel bolts though, some guys used "unbrako's" and they only lasted a few months before they were buggered. Cheers, Terry.

Man I just bought a bolt (90048-300-000) BOLT, HEX. (10X82) for the crankcase, cause it wasn't available on bikebandit, and now I'm pretty sure I don't want to put it on the bike.

casanova · « **Reply #273 on:** April 25, 2008, 06:01:12 PM »

i'm sure this is not the place but i just started to tare into a cb more a 77 and then found out that they ( 77-78k models are slightly differrent ) than prior models . the difference in output shaft/sprocket shaft , can any one else tell me the differences?

smack doogle · « **Reply #274 on:** April 26, 2008, 04:30:12 AM »

Wow!!!! Awesome job keeping the thread going with such enthusiasm. This will help anyone rebuild there engine. I apologize for disapearing from the thread right after me and Legendary started it. My wife got sick (psychosematic seizures) and with that and work and back to my wife spending weeks in the hospital the CB750 project has been neglected. I'll be working on it for the next few weeks but just simple stuff for now. No one know what's wrong with the Mrs. so next week she gets a bone marrow biopsy. Yeah, you know what that means, good old cancer maybe. Anyway, keep up the good work. I'll post and work when I get the chance. Awesome job guys.

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Author Topic: CB750 Motor rebuild... for dummies (Read 245274 times)

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