Topic: CB750 K1 project

[mwvachon]

Cad -> One suggestion on the clutch (for what its worth) If the the plates are all in spec, depending on the age, I'd consider at least replacing the clutch springs. When I did my last rebuild (not the current one -which seemed to get a new EVERYTHING!), the clutch springs measured out ok, length-wise so I only replaced the friction plates. But after riding the bike, I noted a fair amount of clutch slippage. I went back in and replaced the springs. Problem solved. Measuring the spring length doesn't really tell you if the springs have lost their force - and I suppose there is a way to measure that, too; but I'm not aware of any. Just my two Lincolns...

[Dunk]

Since clutch springs are unknown I'll replace those too since they're cheap and easy.

Got a little bit done tonight, sandblasted and cleaned the jugs. I'll do a quick hone and just kiss the head mating surface with a line sander and these should be fine. Cleaned up the head a little bit and ready to disassemble that. My spring compressor won't do these little buggers but I think I can make do with a C clamp and O2 sensor socket. I'll disassemble that and sandblast next time I work on this, hopefully have it ready to do some porting. Not gonna go crazy with these because I've never done this type of head before and such a small engine is probably more sensitive to port changes. Probably focus on light cleanup and shaping them all the same more like the factory did on the earlier heads. Probably deshroud valves, match chambers, and polish chambers.

Ordered a bunch more parts today for the engine, this stuff really adds up quick! Gaskets, seals, screws/bolts, etc... Expensive bits were rings and repop motor mount bolts from DSS. I've got a lot on my plate with other things but trying to keep somewhat steady with this and push through getting the engine done. We're starting to get some teaser warm days so I want to get done soon.

Hondaman's book just shipped... Just in time to be done with this project. Probably should have ordered it sooner.

[Dunk]

Got the head disassembled and cleaned up. Cleaned all the carbon off the valves with a brass wheel and they look decent so I think they'll be fine lapping them in. Didn't measure guides yet but they feel tight, will measure to be sure they're good.









Hondaman's book arrived the other day so I think I'm going to review the head porting section and start working on the ports.

Still need to pull the pistons and clean the carbon off and go over them more thoroughly. I think they'll be fine but I can't wrap my head around why the outer two would be on backwards. Doesn't look like any valve to piston contact though so if everything checks out back in they go. Still waiting my my two orders to ship, on back order or something. Gaskets and orings required to put the top end back together are in those orders so hopefully those go out soon. Haven't pulled the oil pump yet but hoping Elan gets another shipment of oil pump stopper and springs in soon so I can do that before wrapping this up, haven't heard from him and last he said was early this month for the next batch. I had the oil tank and oil pan off a year or two ago and cleaned out a bunch of sludge and nastiness. Don't believe I pulled the pump though.

[Terry in Australia]

Don't forget to run a hone through your cylinders while you've got the pistons out mate, and make sure your rings are free. Cheers, Terry.

[Dunk]

Yes, I will hone the bores and line sand the mating surface to ensure all is well. New rings on order too. What is the recommended orientation for the ring gaps on these?

Got the first intake port mostly done. Aluminum cuts a lot easier than cast iron that I'm used to, which is nice, but I have to be careful not to go crazy with it and the tighter access with smaller intake port and valve access is more awkward then big block heads. Hopefully it turns out well. I'm noticing a lot of inconsistency from port to port as it came from the factory.

[Terry in Australia]

Yep, the aluminum heads ports are easy to grind, I don't use a burr, I just use the cones and rolls to clean up the casting defects and once it's nice and smooth, well, that's good enough for me.

Re: ring gap orientation, I think the manual says to set the compression ring gaps at 8 o'clock and 4 o'clock (with the exhaust valve cutout on the piston at the 6 o'clock position) but the rings will move as the engine is running anyway, so don't worry too much, as long as the gaps aren't lined up, you'll be fine. Cheers, Terry.    

[Dunk]

I think my ports are good. Chambers look like the sharp edges and some shrouding may have already been done either by a PO or this bike was early enough they still did some of this at the factory. At least looks that way when comparing to Hondaman's book. May or may not do any work on these. Been sick as a dog the past week and just starting to feel better. Ordered new exhaust valves and some other misc bits. Two of the valves had some light dimpling on the stem so I don't want to chance that accelerating. Dropped my dial indicator and must have bent the shaft... Irritating, but that's what I get for trying to get anything done while I'm sick.Still waiting on gaskets and so forth, probably clean up the pistons next. and I should just be waiting on parts to reassemble the top end.

Still have to polish the alternator cover and sprocket cover. Bike itself needs a few things done though I've forgot what they are and I haven't uncovered it in a week or two to make a mental note. Hopefully it'll all come together soon now that the weather is slowly warming up.

[Dunk]

Jugs are honed, brushed all holes, cleaned, etc... Head has new valve guides still have to cut seats and lap valves.



Pistons cleaned, new rings sized and on pistons. #2 is ready to go on but pin had some minor galling so waiting on a new one in the mail.



Getting there.

[Dunk]

What's the deal with the little white insulators/rubbers between the fins? I believe they were only on the earlier bikes and not on the later. Purpose to mitigate some of the noise/ringing/rattle/resonation/vibration?  I removed mine and they are very hard as with any rubber part so would need new to replace. Seem expensive or difficult to get. Any reasonably priced source? Worthwhile to replace or just forget them?

[Dunk]

Also did some light deshrouding of intake valve and sanded chambers by hand to polish out some of the marks from original machining. It's getting warm, don't want to spend time to CC chambers so didn't go nuts with it. I may yet, but we'll see. Hoping to have the top end back together by next weekend... Which means engine would be more or less ready to install. That part won't be fun but hopefully I can recruit some assistance.

[Dunk]

More progress...

Air box before:


Air box after washing with soapy water, break clean, then rubbing down thrice with Meguiars Ultimate Black.



So far I'm pleased with the look. Much better. It says not oily, but it has been a couple hours and it is oily after wiping down with clean dry cloth a few times as per instructions. Fingerprints show unless you wipe them down after handling. Felt almost sticky after applying, like it sorta melted the plastic a bit and soaked oils in. Just observations. I'm pleased with the result. Box has a few scratches and scuffs, I'd imagine those would take sanding to fix. Good enough for my goals.

Also completely disassembled and repainted the brackets black. Internal gasket was a little pain to get back in as it was swollen. Cleaned well and used a few dabs of adhesive to keep it in place.

Clutch had plenty of meat left and looked good so I just cleaned, oiled, and reinstalled with new springs. I did drill extra holes in the basket and chamfer as per the tips here. I believe 8 holes evenly spaced and offset from existing holes. Clutch dragged slightly when hot, as they typically do, hopefully this will help.



To do pile:



Bike itself is pretty much ready for an engine and good to go. Odds and ends to do still but getting there.

[Dunk]

Looks more like an engine now...





Bench is more clear than it has been in a long time.



Tired... Shower, sleep.

[Dunk]

Got all these cleaned up, little oddball size orings for under cam towers should be here by the weekend.



Still need to polish alternator cover and repaint the black part. Need to pull the pan and do oil pump orings. And paint the engine, which will be no fun but whatever... Almost there.

[Terry in Australia]

Looking good mate, excellent work. Cheers, Terry.

[Dunk]

Finished the top end. Took some extra time to drill the cam towers for extra rocker shaft lubrication.



Cam timing looks good to me but just to confirm... I initially installed the cam sprocket one tooth over and the cam mark was more to the right. This is almost dead on slightly left I suppose. I think it's alright.





Replaced the countershaft oiler oring. Was definitely flattened.









As far as the engine I believe all that's left is replace oil pump orings, side cover seals and so forth and paint. Masking will suck. I'm thinking of taping up all the covers and installing them then paint that way. Any preferred paint. Probably do either Duplicolor or VHT depending on what's on the shelf tomorrow and what is available in an aluminum color.

Still need to polish the left side covers. Just about there. Starting to dread putting the engine in, I've looked at the various tricks here but doesn't look fun no matter which way you slice it. Probably gonna be a solo affair. Kind of wish I did the engine first and started with that in a bare frame.

[Terry in Australia]

Yeah mate, make sure you wear heavy gloves when you install the engine, it's easy to pinch a finger or rip some skin off your knuckles in the process. I'm building a 750 for another member here but I'm gonna lay the bare frame over the engine to try to save the fresh powdercoat.

I prefer Duplicolor epoxy engine enamel to VHT, it covers very well and the color is close to OEM, and I've had some issues with VHT not being very fuel resistant in the past.

Make sure you use an etch primer first though, or the paint may not stick too good. Do you have an old set of engine covers that you can throw on the engine before you paint? I do that, then just dump them in some thinner afterwards to remove the paint, and that saves me a lot of masking. Enjoy! Cheers, Terry.

[Dunk]

No spare covers unless I tear down the engine from the K1 I dropped years ago. Not gonna do that as that needs to stay compact for the time being. Probably just tape the ones for this engine up well and hope for the best. Kind of wish I didn't sell my first bike, a K2 I sold for $100 after I threw the chain through the case.... Young and dumb stretching maintenance and kapow! Of course I bought the bike for $100 so it was whatever at the time, but we live and learn.

Got the oil pump off and tore down. Some scoring but doesn't seem terrible, given the replacement pump choices of none and not available. Thought I was being smart had the orings and seal on hand months ago and... The three dowels are missing between the pump and lower case. Was gonna say screw it and run without 'em but with my luck an oring will pinch in and cause a catastrophic loss of oil pressure. Parts are ordered and should be here by the end of the week.



Someone has been in this bike and done some odd things. This, half the pistons backwards, apparently dropped the head, etc... Wonder if it was the dude I bought it from who lived on top of a mountain I had to drive up a rutted out dirt road to get to and go stuck and pulled out by a tractor after I broke my transfer case. It was an adventure for sure!

[Dunk]

Any tricks to getting the oil pump shaft seal out of the center main body of the pump? I got it out,  though slightly divoted the center section just below it. Doesn't affect the shaft and won't affect seal after I put the new one in but if if I was just a hair rougher it may not have been as nice. Tried various picks, tiny flatheads, etc. along with heat and penetrant and just tore up the seal but couldn't grip the outer metal part. Honda sure loves to press parts in without leaving any lip or easy way to remove them.

Since I'm waiting on dowels and so forth I ordered two oil pumps off ebay on the chance either is in better condition. The larger rotor in mine is worse which I understand is the return and less critical, but still it's a bit rough. The smaller one is better but took some damage. Outside of pump looks to have been scrubbed with a stiff steel brush and inside looks like it had some metal through it. Never noticed any oiling issues, but never had a gauge on it either.

I'll wait 'till the new pumps come in and pick the best of them to reseal and install. Also stripped some remaining paint off the lower cases and cleaned, more or less ready to paint when the pan goes back on. Don't feel like I accomplished much tonight, but I didn't really spend much time on it. Getting anxious to ride, sick of waiting on parts.

[mwvachon]

Cadunkle - I know what you mean about putting the engine in. This is why I always plan on dropping the bare frame over the engine (meaning the engine and frame finish must be done first). I fought tooth & nail to pull the motor out of my current K1 project when tearing it down - and even with two people, it was difficult. One trick I read about was using a ton of old magazines. Protect the frame as much as you can with duct tape & what ever, and then pile up magazines under & beside the frame so that the engine will be very close to the right height. I've never tried it, but seems easier than trying to muscle the thing in - especially if you're working solo...

[Dunk]

I think when I install it I'll try the pipe straps and jackstands method. Maybe I can scrounge up another pair of hands but I remember pulling the engine out of the bare from on its side was even a little tight. Thought about grinding the top of the motor mount for clearance but I hate to have the frame not be correct.

Got an oil pump in the mail today... Not sure if I'm pleased or not. I think the one I got today is marginally better. Still looks like it swallowed some dirty oil or metal bits. All rotor clearances on the pump that came out of the engine are .003" Spec is .0138" limit (really? type? That sounds insanely loose) The new pump varies .0025" - .003" and rotors don't have staining like there was water in it though there are a couple spots that look like soft metal (bearing material or aluminum) were pressed into the rotor without chewwing it up.

Pump from my engine:













New pump, supposedly from a '74












The bodies are both pretty decent. The '74 pump has a fairly deep scratch on the back of the smaller pressure side of the body but is smoother on each cap. The pump that came off the engine also has a fairly deep scratch in the same area but less deep, though there are more scratches on each cover. Not sure but I'd say maybe the pump body that came off the engine is marginally better and the rotors off the '74 pump are marginally better.

I don't know they both look like crap to me. If this were a Ford engine like I usually build I wouldn't run either of these pumps. Of course even with the pump looking so rough it didn't seem to have any oiling issues from what I can tell of riding it or having the top end apart. Only lack of lubrication looking thing I replaced was #2 piston pin, it had some very minor galling so I threw a new pin in it. Of course that's not pressure fed so I'd imagine the cam bearings or rockers would show problems from poor oil pressure of lack of volume.

Thoughts?? Would you guys run either of these pumps? I do have a pump coming from a '78 (K or F? don't know, I assume they're the same). Maybe that one will be better. I hate to run a questionable pump given how critical it is, but the newest pump I can get is 36 years and who knows how many miles old. Doubt anything being parted out on ebay is gonna be a low miles barn find with religiously changed oil. What to do?

[edwardmorris]

Perhaps this will help you out a bit, I just tore mine down too, and Hondaman was kind enough to shed some light on the matter

http://forums.sohc4.net/index.php?topic=126735.msg1538228#msg1538228

I was concerned about the rotors but the real thing to look into are the covers. There is also a good write up from Mark/Hondaman about how you can determine if you need the lips milled using plastigage, I'll dig around for it and share if you'd like.I tracked down a new screen for my pump and grabbed the two extras that the dealership out in UT had, both my extras were sold almost immediately. If you need one, try calling around a few dealerships or boat shops, Honda is still making these are they are used in their boat engines.

[Terry in Australia]

I hate to admit it, but I very rarely even bother to disasemble a pump on a CB750, I give it a flush with some degreaser, then submerge it in oil, and spin the gear, and if it's pumping OK, I just install it.

I've been doing this for the last 30 years or so, and haven't had a failure yet, so maybe I'm just lucky. I always install oil pressure gauges on my CB750's though, which is cheap insurance. Cheers, Terry.

[rtbmrgl]

I'm subscribed, nice project.

[Dunk]

Thanks for the additional pump info. Side of gears and covers are all fairly scratched on the those though not crazy. Jackpot today, the second pump I got off eBay arrived and it looks good to me. Pressure side clearances are a little looser than the other two coming in at .004" and the larger scavenge side clearances are .003"-.004"... But, compared to the others the rotors and caps are beautiful! Scavenge side took some junk but very minor comparatively speaking but pressure side looks great. This pump supposedly came from a '78 and my first observations were that it is clean on the outside and the oil in it was relatively clean. I'm guessing it came from a higher miles bike that actually had the oil changed.

Anyhow, this pump is good enough for me. I'll finish cleaning it up, replace the orings and seal and throw it in. Wish I had a new stopper but I guess Elan has been busy with his wife and newborn and hasn't got to making these available again. At least that's serviceable in the frame.

[Dunk]

Also one observation I haven't seen noted in any of the oil pump threads I've read here is the early pumps like what came out of the K1 the oil pump shaft is supported only at one end and through the middle of the pump body. The later pumps are supported in the far end cover too with the little recessed area the shaft can ride on. Not sure how much lateral load the shaft gets going through a narrow rotor but the extra support can't hurt.