Topic: 78 CB550K Engine rebuild for scrambler project.

[ruger01]

Hi All,

First post on the forum but I have been reading as a guest for months now, hello to all 

The project:
Myself and my father are currently completely rebuilding a 1978 model CB550K motorcycle, I ended up with the  engine and he is doing everything else etc. This is for my brother who is wanting to turn his recently acquired bike into a Scrambler.

A little help needed:
I was chasing some advise on crankshaft main bearing selection as the ones i have removed have a lot of metal impregnation and are very worn to look at pics attached. I am going to plastigauge them tomorrow but from looking at them I won't be reusing. My current markings on the lower case half are C,B,B,B,B, the crank shaft journals measure out as follows 32.99, 32.98, 32.98, 32.98, 32.98 (all in mm, and measured with a Mitutoyo Micrometer) From reading the workshop manual bearing selection chart I have deduced I will require Black or Brown for journal 1 and Brown for all the remaining four journals 2 - 5. Would you guys and girls agree with this? Also could I get away with just ordering all Brown as I have a line on a set of 10 of these? Reason I am a bit concerned is the current ones I removed are all Green marked except one that I cant see any mark on it. (This one that is unmarked is situated in journal one and it's corresponding journal was the only one that measured .01mm larger than the others) The engine was last pulled apart by persons unknown and it looks like they used a steak knife to disassembled the entire engine there was tons of damage done that has taken a hell of a lot of time to repair. I will post some pics up as to before and after shots of some damage.

I have now completely stripped the engine down and have now acquired most parts for the rebuild but until I order and receive the replacement main bearings I am at a stand still. Thanks in advance for any help and advice.

Kind Regards,

John.

[ruger01]

This is the reason the bearings are in such bad shape - whoever owned it wasn't big on maintenance check out the debris in the sump when it was removed 

[ruger01]

Damage found during the strip down, looks like whoever rebuilt it last time was a pro

[calj737]

Find a new motor. That beaut belongs in the salvage bin.

And 4 cylinder bikes make terrible "Scramblers". Better to find a twin, a CB450 for instance would be a winner. 550s are too heavy, too wide, no ground clearance, and want to have their engine run in the high RPM range- everything a Scrambler isn't.

[ruger01]

Thanks calj737 but unfortunately he is determined to make it as new and wants a Scrambler out of this bike - not my bike so I just do my best

Some pics of repairs to date, its actually coming along rather well, thank god I have a mate who is very handing welding aluminium.

Head fin damage repair as well as valves recut. I also received the engine cases back from blasting they came up a treat prior to sending them over there would have been 5 hrs of scrubbing and pressure blasting.

[calj737]

Yes, your mate did a fantastic job welding those cases. Really nice work. The repair on the crank journal (the exterior seal), that needs to be machined to a pretty careful tolerance. Before you go too far forward, best to have that inspected with internal micrometers and check for fitment. (In case that had not occurred to you 

[ruger01]

Yeah calj737 - this seal area needs more work not seal ready yet but will be.

I have been receiving new parts all week, must be driving the post man mad!? Bloody primary chain wasn't cheap $179.00AU, the electronic ignition kit arrived as well as a new chromed points cover, S/S engine screw set, cam chain and gasket/seal kit, clutch springs and friction discs. A new set of standard piston and rings etc arrived as the bore measured out very nicely after honing to 58.51 - 58.53mm between all four cylinders (I had them machine honed in town and they came up very nicely. His new 4-1 exhaust is here a Delkevic one looks very nice and well built.

The cam shaft is toast the lobes on cylinders 3 & 4 are worn severely, lobes on cyl 1 & 2 look perfect and measure well within spec. I have ordered a good secondhand one from the states as well as 4 new rocker arms as the chrome was worn from this same side of the engine. It appears it was oil starved a bit on one side of the engine? To be investigated, and I will pay close attention to the oil galleries and oil pump when its time to rebuild.

I did also manage to get the kick start shaft back in today, a couple of bearings in as well as the starter motor gear. Crank is sitting on old bearings awaiting plasti gauging this morning to determine replacement main bearings shell sizes.

[calj737]

There’s a member, Elan, is in EU, he sells an oil pump rebuild kit with ALL the requisite and unobtainable o-rings. Think it’s about €20.

There’s another member, Mike Rieck who is a fantastic head guy. Unfortunately he’s in the States. But the point is, he always slightly opens the oil passages in the cam journals when he does his magic. You can do that as well, or a machinist locally. Should help with oil flow on the cam.

[ruger01]

Thanks mate I will definitely do the oil passage enlargement there is serious oil shortage on r/h side of the camshaft.

I just tension the case together over the crankshaft journals with old green bearings fitted (one unkown coloured one in position 1)

Results: Journal 1: .076mm, Journal 2: .076mm, Journal 3: 050mm, Journal 4: .050mm, Journal 5: .050mm.

I am lead to believe the clearance service limit is .08mm (.0032"). Journals 1 & 2 are pretty much at that.

Would any one care to advise if brown bearings throughout is the way forward?

Cheers,

John.

[ruger01]

Some more work done today, the rocker cover reassembled with 4 new rocker arms fitted. I managed to get my main bearing shells ordered (set of 10 brown ones I went with) Still waiting on a new inlet valve, once it arrives I can reassemble the head. I received the primary drive cush rubbers so will replace them tomorrow.

Got some sanding and polishing to do on the stator and chain guard cover. Also managed to sort and tag all my bolts that didn't come in the polished s/s bolt kit I have.

I had to buy new head stud flanged nuts as the old ones were cactus. Anyone see any problem using serrated faced flanged nuts with washers under them?

[754]

You mean to torque the head ? I would not use that.
 Just grab some used ones if you can't find new.

[ruger01]

Hi 754, yeah was going to use them with washers underneath, I turned every fastener shop upside down looking for the smooth ones no luck. Checked out flea bay Australia an no deal seem to be able to get s/s ones no worries. I have access to a lathe I guess I could face the serrations off?

Postage for us down here is an absolute killer.

[RAFster122s]

Do you have a list of all the parts other than seals, orings, and gasdkets you are replacing with new parts ? Curious but also interested in seeing how deep into the bowels of the motor since you are replacing primary drive rushes. I too ordered them for a rebuild.  Nice work on everything you are putting a lot of effort into moving this along.

On the camshaft, if you are buying a hardwelded reground camshaft, only new camshafts I am aware of existing other than a rare NOS  Yoshirmuri , you must also use hard welded rocker arms. Your motor does have a pinned rocker arm design, not unheard of bikes this old getting cobbled back together and the 74-76 covers are not  pinned and have eight short shafts instead of four long shafts pinned at the breather cover. Beneath the breather cover will be eight nuts instead of four when you have the later design used on77-78 bikes. But you would definitely see worn rocker arms for that side as well.
David

[ruger01]

Hi David, yes I have the pinned rocker cover design has the 4 pinch bolts in it.

I have been keeping a spreadsheet of all parts ordered with costings. Off the top of my head and so far ordered: 8 new tappet adjusters, 4 new rockers arms, a secondhand camshaft, one new inlet valve all others reground as well as valve seats recut, cylinder honed and both head and cylinder bead blasted, 4 new pistons and rings sets including  pins and clips (standard size) new cam chain, new cam chain tensioner blade, oil pump oring kit, new primary chain, new cush rubbers, 3 new roller bearings in bottom end, new brown main bearing set, electronic ignition system, s/s screw set, all new seals and gaskets, hockey puck rubbers for the head,kick starter and gear lever rubbers, clutch springs, friction discs, and new chromed points cover. Also the engine cases wet bead blasted after damage repairs were done. We also sourced a new exhaust system.

I did find one conrod is slightly twisted e.g. doesn't lay flat like the others on a sheet of glass, so found a good secondhand one I will replace it with. Thats the damage so far and am slowly putting her back together, waiting on parts at present but have 3 covers to polish.

[RAFster122s]

Nice Mate! (If you will forgive my TN Hillbilly using an Australian venacular    )
A nice performance camshaft would be good for a street bike but I don't know if the CB650 camshaft would be a better choice for what you want to do as it enriches the breathing across the band and gives some better top end. The 550 makes it power above 4K and really is happiest and on cam at 6K and beyond to redline and with work the redline can be taken up to 10.500 with the right work without too much trouble but beyond that I think it requires lots of expensive work and valve train work. Not something a scrambler will see.
If he is going to have a scrambler, don't let him put big knobby tires on it if it is going to see street use too? I really is suitable for street and might allow him some light off-road but as many have pointed out it simply does not have the suspension travel for it. A TransAlp/AfricaTwin or other bike would be a better choice or a dual sport bike. There are some tires that do street decently and have a block tread that will allow him to do some off road work as well. Knobbies are going to be close if not dangerous on city streets wanting to lock up and slide way way too easy.
I have seen street bikes pressed into off road and they just are a disappointment.
If you check the boxes for his scrambler, ensure it can be returned to street bike without trouble as a nice street bike like it was designed to be is going to sell better if he ends up selling it. (Would be a shame to see that happen after all the work you are putting into the motor. Having the frame be uncut is probably asking too much as he is likely to want a thin height brat like seat, just caution the other fellow working on the frame that he must, MUST, make sure the bike is not going to impact the rear seat when the rear wheel goes full suspension travel. It will frequently if he intends to ride it over rough terrain. Over springing the rear shocks like the cheap Emgos is going to make his back hurt from the pounding they will be giving him and being over sprung in the back the poor front suspension is going to be diving in response so, he will need to be running heavier oil and springs up front  to try (futile effort) to balance the suspension with the nasty Emgo shocks. The Emgos might work if he weighs 300+ pounds...but again the front is going to be running very stiff shock oil and need heavier springs. That is the opposite of most off road bikes as their long travel absorbs the shock and their springs (long progressively wound) and oil is lighter to allow that front suspension to not punish your wrists,hands, and shoulders and really your body when you hit a rut or similar off road traveling with some speed.
 
I hope he is happy with the overall looks and can be convinced it will do light off road or smooth off road but it is and always will be a street bike.  I hope he doesn't get hurt on the bike.


David



 

Hi David, yes I have the pinned rocker cover design has the 4 pinch bolts in it.

I have been keeping a spreadsheet of all parts ordered with costings. Off the top of my head and so far ordered: 8 new tappet adjusters, 4 new rockers arms, a secondhand camshaft, one new inlet valve all others reground as well as valve seats recut, cylinder honed and both head and cylinder bead blasted, 4 new pistons and rings sets including  pins and clips (standard size) new cam chain, new primary chain, new cush rubbers, 3 new roller bearings in bottom end, new brown main bearing set, electronic ignition system, s/s screw set, all new seals and gaskets, kick starter and gear lever rubbers, clutch springs, friction discs, and new chromed points cover. Also the engine cases wet bead blasted after damage repairs were done. We also sourced a new exhaust system.

I did find one conrod is slightly twisted e.g. doesn't lay flat like the others on a sheet of glass, so found a good secondhand one I will replace it with. Thats the damage so far and am slowly putting her back together, waiting on parts at present but have 3 covers to polish.

[ruger01]

HI RAF, thanks for the advise on the suspension.

I can guarantee this bike will never see dirt, it will remain a street bike that has a very shady resemblance to a Scrambler... Think renthal handle bars, custom gauges, modified seat/pan, custom paint, different side panels etc. I don't believe he is hooping/cutting the frame at this stage. (It will get ridden to the shops and on short sorties on the highway at best)

My father got the tyres fitted to the rims yesterday pic attached, the tread is definitely more street than knobby that's for sure, I like them though. I managed to install the valves back into the head except for the one I am waiting on to arrive. Got some sanding polishing and painting to do today that I have been avoiding.

[ruger01]

Well it was a productive day yesterday I managed to get the alternator cover shining like new after hours of work sanding and polishing (i had to lose the "Made in Japan" stamp as the bottom on this side was badly scored up) looks pretty nice now though. The clutch cover, chain cover and breather cover are now painted after more hours priming sanding and painting, I went with matte black on these.

More parts arrived some from the good ole US of A, the camshaft which is in great shape and measures out well within spec for cam lobe heights etc. The tappet adjusters arrived from Germany and i got them screwed into the rocker arms. I also spent and hour or so with a 6mm tap going over all the case hole threads to clean em out. I ordered an oil pump rebuild kit from Elan (thanks mate) and I see its on its way already Some other bits I realised I was missing were the 6 rubber pucks for the rocker cover that were not in the gasket set, the 3 oil gallery o'rings on the lower engine case half caps - these all now ordered.

I have to fabricate a plug/cap for the tachometer hole in the rocker cover as we are putting a digital speedo on the bike and the original cable won't be needed. I did find these on Ebay but postage is way to high.

Some pics for anyone interested.

[ruger01]

Hi All,

Another update:

I managed to get the clutch cover seals and mechanism reassembled yesterday, initial installed the shaft 180 deg out  Also got the stator and coil reassembled into the cover I spent hours polishing I tested it all with an Ohm meter and the coil tested (inner part) out fine but the the Stator (outer section is suppose the test at .35ohms plus or minus 10% mine however is at 1 - 1.1 ohms not sure if this is stuffed or going to cause issues anyone got an idea or comment?

The kick starter shaft and transmission as well as associated seals has now been installed into the upper crankcase as well, now waiting on parts (main bearings etc)

Cheers,

John.

[ruger01]

Hi All,

Well it's been a busy few days, I actually managed to get the engine cases back together as the main bearings and conrod finally arrived. I got the pistons and barrels back on as well as the head. Managed to fit up the electronic ignition a Japanese branded one (Kokusan) got the cam timing set as well as the ignition plate. The clutch is installed as well as the starter motor.

The engine rolls over very nicely, I can't do anymore until some rubber washers turn up for the rocker cover as well as some o-rings. Pics attached if anyone is interested.

[ruger01]

Well finishing this one up...

I received the oil gallery o'rings, oil pump rebuild kit and rubber pucks for the tappet cover/head so managed to finish the ole girl off after a struggle with some stripped out threads (had to remove tappet cover and repair 4 stripped threads in cylinder head)

Currently waiting on the rolling frame to arrive to be able to help my father install the engine back into the frame, then we can test run her. My dad is rebuilding the carburetors presently should have then done in a few days.

Some pics of the end result, definitely worth the effort and cost to rebuild instead of ending up in land fill...

[SOHC4 Cafe Racer Fan]

Pretty looking motor.