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

[edwardmorris]

I'm impressed with your thoroughness.  Nice work!

What is the specific eastwood product you're using?... I might do the same thing with my frame.

Its called the internal frame coating, easy search on their site. There is a link to it in the frame scare thread, pain to type it out on this puny tablet.....and thanks!

[edwardmorris]

So the frame is on vacation at the weld shop, swingarm is out seeking a new life and don't have everything to rebuild the MC. Gathered all the courage and tore into that engine and surprise! Looks like the PO did a great job on the head! Time to close it back up? NOOOOO, its the PO I'm talking about here. Something was already fishy when only three of the 19 screws for the valve cover were so incredibly tight, and the rest came undone with a push from a finger tip. Clearly evident when I took the cover off, the gasket under the tightest of screws remained stuck to the head, rest came of intact. Ah, all these nice shiny red thingys, lets take a closer look and there it was, FAILURE #1, the bolt holding the rocker shaft for #1#2 exhaust side is playing the spinaroonie! As is the PO over tightened and stripped the poor bastard. I pulled it out, and look at the threads.

[edwardmorris]

I've managed to get the rocker shafts out for #3#4 inlets and #1#2 exhaust sides, but the cam is not aligned where I can get the other two out. I tried turning it by the chain, won't budge. I loosened the tappet adjusters out all the way but its still pretty stuck in there. The factory manual shows someone using a hammer to drive it out, but that looks dangerous. Won't this destroy the smooth surface of the shaft? Suggestions on getting the remaining two out?

[MCRider]

I've managed to get the rocker shafts out for #3#4 inlets and #1#2 exhaust sides, but the cam is not aligned where I can get the other two out. I tried turning it by the chain, won't budge. I loosened the tappet adjusters out all the way but its still pretty stuck in there. The factory manual shows someone using a hammer to drive it out, but that looks dangerous. Won't this destroy the smooth surface of the shaft? Suggestions on getting the remaining two out?

IF you remove the ones you can remove, that will loosen the spring tension a lot. From 8 springs to 4.

There's a reason the engine won't turn? I haven't read your history. Normally you'd turn the cam by turning the crankshaft at the ignition nut. IF the engine is locked up, cut the chain with a dremel tool and turn the cam with the nut on the end of the cam.  Are you going to replace the chain anyway?

You're right, you don't want to drive those shafts out with spring pressure on the rockers, although it would probably work without damage.

[Davez134]

I've managed to get the rocker shafts out for #3#4 inlets and #1#2 exhaust sides, but the cam is not aligned where I can get the other two out. I tried turning it by the chain, won't budge. I loosened the tappet adjusters out all the way but its still pretty stuck in there. The factory manual shows someone using a hammer to drive it out, but that looks dangerous. Won't this destroy the smooth surface of the shaft? Suggestions on getting the remaining two out?

Have you tried turning engine over with kick start lever a little bit at a time? Going to be real hard to turn over just by trying to use cam chain. That's what I did to get mine out.

[edwardmorris]

IF you remove the ones you can remove, that will loosen the spring tension a lot. From 8 springs to 4.

There's a reason the engine won't turn? I haven't read your history. Normally you'd turn the cam by turning the crankshaft at the ignition nut. IF the engine is locked up, cut the chain with a dremel tool and turn the cam with the nut on the end of the cam.  Are you going to replace the chain anyway?

You're right, you don't want to drive those shafts out with spring pressure on the rockers, although it would probably work without damage.

Thanks! The engine was essentially "running when parked", I took off the points cover and turned  the nut just enough and they slid right out. As for replacing things, I'll follow the inspection steps and see if it is necessary. Knowing this bike, it might need a lot of new things. It went well after that and head needs to come off next. Taking a break, reviewing Hondaman's book and the manual, then will proceed with caution. On the surface, all the rubbers and seals seem to be in place. No idea what that blue goop is though. Also, the bearings still have the factory markings, that's a good sign. Being the compulsive paranoid that I am, I put it all back together in a dell box I found around the house.

Any suggestions on how to deal with the one bolt that is stripped?

Thanks all for the help.

[Davez134]

You can go a bigger size, helicoil, or the product I used was Time-sert. It's more pricey than helicoils but a permanent fix. I have some pictures of it on my build thread at bottom of my signature. I had the same problem

[edwardmorris]

You can go a bigger size, helicoil, or the product I used was Time-sert. It's more pricey than helicoils but a permanent fix. I have some pictures of it on my build thread at bottom of my signature. I had the same problem

Thanks for the tip! Where did you buy those? And wow, totally digging those black fenders, the whole bike looks suweeet!

[Davez134]

Thanks man! I got them from Amazon.com.  The size I used was M6 x 1.00 x 12mm. I ended up ordering extra inserts cause I thin kith installation kit only came with 4 or 6. I ended up putting those in all the ones that had been helicoil-ed previously. ( I didn't want any future problems)

[Tews19]

I haven't really been on the site much lately but aren't those HI-PO valve spring and retainers?

[HondaMan]

Interesting head you've got there! It appears to have uber-strong springs and aluminum or titanium spring retainers. Was someone building a race bike? They are most definitely not stock parts.

...which may lead up to the issue with the stripped bolts. First: on the pre-1974 (K4) bikes, there were only about 7 threads in the head for those bolts. Their main purpose appeared to be: hold the cam towers in place while the rest of the head was being assembled, and help to seal the

rubber head puck. In the early K0 manuals, it noted in no uncertain terms, "Tighten these bolts to only 70 in-lbs", which disappeared by the K1 manuals. If they get set to the more typicla 90-100 inch-lbs, the threads let go. Later heads have full-length threads, which are more expensive to make in production, but I suspect they were getting negative feedback from shops by them, and 'fixed' it.

When I 'fix' them (in fact, on every head I do), I install 2 short Helicoils in each hole. This provides a couple of things: 1.) The bolts can be torqued to 90-100 in-lbs if you want to, and 2.) the small gap between the 2 Helicoils traps some oil in there so it won't stick later and cause one of them to back out on the next disassembly.

When yo do reassemble, only tighten those bolts until the shaft stops spinning, then back it off until they will turn again. They are supposed to let those shafts spin on the pre-K3 heads.

But, a note of caution here: if those springs are indeed HD types, consider getting some of the post-K2 shafts and drill those rocker towers to accept the little 5mm bolts (8 of them) as shown on the later heads. Then, if the HD springs cause a fractured rocker shaft, it won't wander out and cause any further damage (it will just make a clicking sound when running). -- Or, just use stock springs?

[edwardmorris]

Thanks Hondaman and Tews. Is the HD/HI-PO a good thing or a bad thing?

I highly doubt the PO was racing this thing, give how stubborn the front brake was when I bought it. Then again, I bought it from a guy here in IN, yet it had a (clear) Michigan title. Can't really tell what that owner may have done with it. If he did race it, then I'd really worry because racers tend to not use the clutch when shifting. There was a time after I got the front break taken off where I tried to ride it. Shifted into first and a loud craaaaaaaaank sound and then bike shut off. Yet, at the time of delivery, the seller got on it and shifted through a few gears (in place) with no noise. At this point I'm half certain that the tranny has some damage. This is one of the biggest reasons I wan't torn down to the last bolt. Heard too many horror stories of trannys locking up at high speeds.

TBH, it sounds easy but expensive to just replace with stock springs, rather than finding later year shafts, unless there is a way to definitively find out the ones on there now are in fact high performance.

[Terry in Australia]

G'Day Edward, as Mark suggested, the stripped threads could be as a result of the heavy duty valve spings and (possibly) a high lift cam, which can overwhelm the pissy standard 6mm screws in the soft alloy head casting and actually tear the cam towers off the head. RC (and now CycleX) sold a cam cover with special threaded plugs welded in for "hold down bolts" that screwed down onto the cam towers to stop them from jumping off the head.

I'll be interested to see some pics of the cam, to see if it's a stocker or not. To check,  undo the bolt on the #1 cylinder end and see if there are any markings on it, like the brand name, model #, amount of lift etc. Also, it'll be interesting to see whether or not it's running a big bore kit, whether the ports have been played with, valve sizes, conrods, etc etc. It could well be that you've got a hotrod engine there, which would be cool.

The blue stuff is some kind of sealant that's been applied to the rubber "pucks" to stop oil leaks, don't forget that there are four 6mm screws under those pucks and you'll need to remove them before you can seperate the head from the cylinder block. The horrible noise you mentioned when you tried to shift into first probably wasn't fatal, more than likely the oil was cold and your clutch plates were stuck together.

A good habit to get into is to (once your clutch is properly adjusted) is when warming up your engine, pull the clutch in a few times to get some warm oil between the plates, which will reduce the "craaaaaaaaank" sound, to the standard CB750 "Clunk" when you shift into first. Have fun! Cheers, Terry.    

[edwardmorris]

Thanks Terry, I can breathe a little better now that I know that the trans may not yet be dead. I will take some better pix of the cam and post soon.

[edwardmorris]

Here are some pix of the cam. Couldn't get a good pic of the cam bolt side because of poor lighting/too much glare. Didn't see anything written on it though. Also, turns out that all four of the rocker mounts have helicoil in them, so the PO managed to strip them all first, helicoil them all, then strip the damned coil too, ugh.

[edwardmorris]

So anyway, I moved on and removed all the head bolts, and it almost felt like they were unevenly torqued. Some snapped loose with little effort, others made my abs tight. I wonder if oil was leaking and they torqued those ends down harder? Who knows. I was able to remove the head just by going hulk on it, don't think any gasket sealant was used and it pried right open. Pistons look alright, what do you guys think?

[edwardmorris]

I managed to pry the jugs loose with little effort (hands only) but it seems pretty damned stuck on the front right (#4 exhaust). I've tried cutting our the gasket with a razor blade and its so packed even the blade can't quite get in all the way. I cut out as much as I could but I can't really get it to budge. Any suggestions on breaking that bond loose? With the blade, it feels like there's a tube/dowel around that stud, I wonder if it has corroded away. The one on the front left popped out easy though.

[MCRider]

re: Cylinder removal. YEs there is a dowel on that front right stud (front left too). They can get corroded and stick. Place a teeny tiny chisel on the side or front of that stud, in the gasket material, and tap lightly. Squirt some penetrant in there if you can get it to separate a tad.

[Terry in Australia]

Thanks Terry, I can breathe a little better now that I know that the trans may not yet be dead. I will take some better pix of the cam and post soon.

No worries Edward, that cam doesn't look like a stocker, are there any other markings on it? Is the cam sprocket "slotted", so you can adjust the cam timing? Anyway, that'd explain the heavy duty springs etc, if you take Mark's advice and replace the springs with stock springs, you might need to swap out that cam for a stocker.

The pistons look like stockers, although they could be oversize, you'd need to measure the bores to find out. Shine a torch into the inlet ports and see if they've been modified, if they have they'll look and feel pretty smooth. If they haven't, they'll feel pretty rough and there'll be some "casting marks" in evidence.

Re: your torn out helicoils, the "Timeserts" that Davez134 mentioned will fix that problem, just follow the instructions to the letter. I don't know how deep you want to go into your engine, but if you drop your oil pan and there aren't any big chunks of metal in evidence, and if you grab your conrods and can't feel any upward "slop" in the main or "big end" bearings, you probably don't need to delve deeper, unless you really want to.

If you decide to go further, make sure that you've got a digital camera to take lots of pics of what it looked like before disassembly, plus a copy of the factory parts manual, (for exploded diagrams of the various assemblies) and a workshop manual. A lot of guys here get overwhelmed on their first engine rebuild, and end up "shelving" their projects, but if you do it carefully and methodically, you'll have no problems. Cheers, Terry.

[edwardmorris]

Thanks for the input Terry! I'm sure as hell going all the way through this one. Wanna rebuild it once and do it right so I have it for making seconds notice trips when I go hunting for my next bike . A buddy of mine printed and hardbound the factory manual for me, I've got Mark's book, I've got Gordon's JIS driver kit and I have the entire bike's fiche set up as wallpaper in my workspace (pix earlier in the thread) so HOPEFULLY I'm set to get this done right.

There is a picture of the cam sprocket in my earlier post, does it look stock?

I really appreciate everybody making time and helping out.

On to the problem at hand, McRider, I couldn't find a teeny chisel, but something like it in a utility pliers set worked like a charm. I got it budge just enough that all the oil around it soaked right in. Gave it a minute and the block started sliding. Gently rocked it out and there it was, rusty crud. The other side was pretty clean.

[edwardmorris]

Pistons look to be stock, jugs look clean with no visible scratching or damage. The cases show its still a 736cc but its possible some other shop did do a bigger bore on it. What is the best way to measure the bore size? I just have digital calipers, not the fancy cylinder gauge.

[MCRider]

Glad you got the cyls off. Get a teeny chisel next tool shopping day, they come in handy. Blade is about 3/16, shaft is about 1/8" hex.

Don't need nothing fancy to measure overbore. stock is 61mm. first popular overbore is 811; 64mm (you can judge that with the naked eye). next popular oversize is 836 = 65mm. Next is 850cc (largest overbore in stock sleeves) = 65.5. Can be measured with a wooden ruler.

1mm = 1/25"

(Use 63mm stroke with this calculator:)
http://www.nightrider.com/biketech/calc_displacement.htm

[Terry in Australia]

Yep, what Ron said Edward, also, as i mentioned before, those pistons look like OEM Honda, but they could be oversize, so they could be .25mm, .50mm, .75mm, or 1.0mm oversize.

Get you digital caliper and measure across the thrust faces of the pistons (the front and back, basically) about an inch 25mm up from the bottom of the piston skirts and see what your caliper tells you. Your pistons should be no more than .10 mm under the cylinder size, so if the cylinder is 61mm (standard) you'd expect the pistons to be around 60.90mm.

You can buy cheap telescoping bore gauges on eBay to measure your cylinders, I use a cheap set when I rebore cylinders, you poke 'em down the cylinders, lock them by turning a screw in the base, then measure them with your digital caliper. Cheers, Terry.

[edwardmorris]

Thanks Terry, I will measure those today and post back. Did you get a chance to review the cam sprocket? I can post more close up pix if needed.

I got further last night, was too tired to post but I'm pretty close to getting the cases split. Pistons are out, clutch cover, alternator and the shifter cover. Have I mentioned how AWESOME the JIS driver kit is yet? I've managed to break an impact driver long before I got anywhere near the engine. The impacta in Gordon's kit is the real deal. I managed to get all screws out with little effort. There were two on the shifter cover that had been stripped beyond hope by the PO, so I had to drill those out. Now I need to figure out how to get the points plate off safely.

[Terry in Australia]

Looking good mate. Be careful when you disassemble your clutch, if you don't back those screws out evenly you can break the outer plate, so you'll need to back one out a couple of turns, then the one diagonally opposite, and so on and so forth.

You'll need a special tool to remove the centre clutch nut, you can buy one on eBay or make one by "modifying" a socket with a grinder. Don't do what most people do, and take a screwdriver and a hammer to it.

Oh, I looked at your cam sprocket, but it's a stock item. Some milder street cams didn't need a slotted sprocket though, so you need to take a closer look at you cam, and measure the lift to see if it's a stocker or not. To measure it with your digital caliper, measure it from the "heel" to the "toe" (you may need to "roll" the cam a little in the caliper to get the highest possible measurement) then subract the distance acoss the base circle. (draw an imaginary line across the centre of the camshaft's non lifting planes and measure it there)  Cheers, Terry.