An Easter story on seals and camshafts.

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Volker_P
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An Easter story on seals and camshafts.

Postby Volker_P » Tue Apr 25, 2006 1:23 am

As announced, I spent Easter to work on my CB. Weather was not too cold so I did the job in the garden under a roof with the radio on. It came close to something like active holiday.

Main reason to start this was too much oil on my boots from the cylinder to cylinder head gap. Second reason was to find out how it will run with the 63hp camshaft :-) (this part is the last three paragraphs only). Below is a quite lengthy report for those who like to read such stuff.

I started Thursday evening with getting off the carbs and clean them for some hours until I was tired. There was only a bit very fine rust in the floater bowls. The choke cam on Nr. 3 has free play but the Nr.3 spark plug does not look like lean so I leave separating the carbs (and running after small O-Rings) for next winter.

I had a look on that plastic lever for the choke which was considered to be susceptible. I never had trouble with it and I think I know why. This lever does two things. First it is turning the choke flaps which is done via weak springs so here no heavy mechanical load can occur. In the worst case the flaps only close partly or only at one side (the choke cam is divided in left for 1+2 and right for 3+4. However the black part also opens the throttle a bit by a kind of excenter. There is an adjustable (metal) counterpart which allows to set the choke throttle opening. In my case it does practically nothing, maybe this explains my starting problems. But if the black part surface is not smooth at that point, if may be caught and blocked by the counterpart and metal will win against plastic when you try to pull the choke with force then.

Friday was the day of the main work. It took me about 11 hours with most of the time spend on cleaning stuff. First I got off as much dirt as I could with the air compressor as long as the engine was closed or plugged. I released two rocker arms under load. The cylinder head cover bolts were hard to open, however all survived. I considered to use only the lower torque limit this time. Then cover and camshaft was easy to get off and out and I placed it on really flat wood on newspapers. I had a look on the camshaft mark and the T1.4 crankshaft mark to confirm that the position is really unambiguous. I did not remove the long rubber seal. The cylinder head was not that easy, there was a considerable amount of mud and small stones especially on the two front center cylinder head bolts. I was quite patient to get that out and used a 6-surface nut to make sure not to kill a screw. It has been eight years since I had them out and I also feared to kill them. Well, I again was lucky and they survived. The cylinder head was also placed on a newspaper part on a very flat wood part. Then I took off the head gasket and also placed it on a newspaper. The two O-rings of the oil pipes to the camshaft were flat and hard, this was the reason for the leakage. I noticed that the step machined into the cylinder bank has a quite rough surface. Maybe one could delay or even avoid that leakage problem by polishing this surface but I did not want to take off the cylinders.
Then the most time consuming thing was to clean the threads of the cylinder head bolts. A long 6.5mm drill turned out to be the ideal tool to get out the dirt off the holes by hand. Then you carefully turn in a screw to get the dirt out of the windings and repeat with the drill. Clean the screw, and again. Well, I think it took me two hours or so until I found out and managed this job but better than a damaged thread. Then the most sensible part was on the schedule: cleaning the cylinder, the cylinder head and the gasket. I wanted to reuse the old head gasket with only the two O-rings new so I cleaned everything very carefully with acetone and my finger nail to make sure to cause no damage to the surfaces. I also removed some carbon from piston and valves but only in the center where it was thick and easy to access. No risk to cause scratches. I checked the chain tensioner but without removing it. So far it was three o'clock and I had something to eat and spent 15 minutes in bed to get ready for reassembly.

To have a chance with the old head gasket I use a high temperature grease (looking a bit like copper powder but like grease, dont ask me what it is, it is probably even older than myself :D ) which I smear on the metal surfaces in a very thin (still almost transparent) layer. Everything has to be perfectly clean. Then I mounted the cylinder head and put in the bolts with some grease. Most of them run in easily the first 13 turns but one center front one got on strike after 6 turns. I did not want to take a risk. My drill was long enough even with the head mounted but I did not have much success. Probably a small stone got caught directly in the thread. I spend some time trying out things, the job was finally done by a small circular wire brush. After that, things went quite straightforward. I tightened the cylinder head bolts with a hightech digital torque wrench to 25Nm in several steps following the scheme in the book. I put in the spark plugs and got the camshaft chain with a bicycle spoke. Some MoS2-grease was put in the camshaft bearings before it was installed. I also put somewhat on the lobes but used ordinary grease on the 6 rubber plugs. I put some locktite on the camshaft sprocket bolts. The tensioner had a gap of a few mm that was pullled tight with the upper screw. The adjustment screw was released to check the alingment of the camshaft mark. After making sure that the surfaces are perfectly clean and no rocker arm will be under load, I mounted the cylinder head cover.
Then I released the rocker arms which were still under load :D.
Now the hightech torque wrench was useless as it starts at 10Nm (and shows nothing below because acuracy would be below the 4% specification or so) and I had to use my prehistoric one made from a dinosaur bone by Fred Flintstone himself. I could at least calibrate it above 10Nm with the hightech one and this old tool was not too bad. I spent some time tightening 22bolts in 5 steps to finally something just below 10Nm changing nuts and flexible parts in the center where the frame hinders somewhat and also turning the handlebars from one side to the other following the crisscross pattern. Next time I will fix it temporaryly a bit to the front. Then valve adjustment again turning handlebars. Finally I filled in oil in the reservoirs below the camshaft before I closed the engine covers. For installing the carbs, I should have removed two carb boots as usual but it worked also with four. I noticed for the first time (or I just do not remember because I am that damned old) that the airbox side carb boots are turnable and excentric to adjust height and spacing, may be important when changing from PD to CV carbs. I also managed to put on the exhaust and burn the most oily newspapers before it got dark.

I was a bit surprised because I did the whole thing quite silently and without getting angry or crying "shit" to be heard some miles around. And I did not bleed like hell. Now I start to get doubts how much these things are really necessary for success. :P

Saturday was the only day with good weather announced so I had to get it ready. Unfortunately my gas wire started to split off and so I spend some time of the morning by crawling below the workbench in the dust to find my brass end part that fell down during removal. I finally got it and screwed and soldered it to a new wire so I had a complete bike at noon.

Of course I was very interested because I did not use my original camshaft but put in a 63hp one which looked not too bad, at least for a test. I took my stethoskope and it started quite easily and ran as usual, besides the clutch rattle and intake Nr. 3 (I guess my rocker cam is bend a bit, I so far always forgot about that when the head cover is off) quite silent for its mileage. It is always good to see that you are still able to put something together and it just works.

Anyway, got my motorcycle stuff and went out for a ride. Robert, did you hold the line? The engine ran quite allright and I decided it is worth to check it in the hills outside the flat rhine valley. I think the 63hp camshaft provides a smoother engine characteristic and somewhat more torque in the whole rpm range. It is not dramatic and no different engine but it provides a bit more where you really can make use of it. I always had concerns about riding with two people but this should be no problem with that camshaft. No big deal, but also not going crazy with the gear lever.
I think the 63hp camshaft fits better to the engine. Rejetting seems not necessary, at least for me it ran just perfectly. However I only tested until 6000rpm (then I start catching attention by an impressing smoke tail) with a 17 front sprocket (which corresponds to a 16 on a Z-model) to list the boundary conditions of my subjective impression. The engine seems to be also tight, there was still oil on it before I started but nothing got on the boots during about 100mls. I did not check for differences in fuel consumption accurately but it is definitively still below 4.5l/100km.

I however did exchange the camshaft again with the 50hp one as on one lobe the hardened surface is broken out somewhat. I had it at an engine workshop to get an experts opinion and they told me it should be and can be rebuild for about 120-150EUR. I meanwhile did another run with the old camshaft and I still like my CB so the difference seems not that decisive. I have to go to TÜV (German technical inspection every 2 years) in June so this would be considered as the date for legalizing the higher power in case I should have a good camshaft by then. Any offers of really good, cheap 63hp camshafts (let's say not too much above 50EUR) are welcome :lol: .

Finally, that's it!

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Ibsen
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Postby Ibsen » Tue Apr 25, 2006 5:54 am

It seems like you had an enjoyable easter. :D It's good reading.

I wonder if the grease you used for the head gasket might be Copper Grease. It's been around for as long as I can remember, and still is.
The problem with the plastic lever for the choke seems to be that they are fragile and can easly brake off when you take the carbs off or when you install them. Btw, I adjusted the fast idle on my carbs last summer, and it made a huge difference.

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Volker_P
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Re: An Easter story on seals and camshafts

Postby Volker_P » Tue Apr 25, 2006 7:34 am

I agree the fast idle adjustment would make sense as it starts better with the throttle slightly opened by hand. I was not aware of that adjustment screw so far. After getting the black dirt stuff off, the adjustment screw turned out to be sealed with some yellow paint. Another point is that below the circular cover on one side of the carbs there should be an air cut valve. At least my manual says so. Well, there was nothing below the outermost one where I had a look. I will check out whether my spare carbs have it. As I did not have any carb problems during all the years it could be not that important anyway. Would maybe again helpful for starting.

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Ibsen
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Postby Ibsen » Tue Apr 25, 2006 11:34 am

I can't tell for sure, but I wonder if some of the European models came without the air cut off valve from the factory. And I agree, if it runs good as it is, you shouldn't worry about it.

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Re: An Easter story on seals and camshafts

Postby Volker_P » Wed Apr 26, 2006 1:25 am

That's interesting to hear, I am sure I did not throw them out and the previous owner did also not look like someone who tries out carb modifications. But now I am curious and I guess I should have two or three other carb sets to have a look inside.

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Ibsen
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Postby Ibsen » Wed Apr 26, 2006 7:11 pm

I could be wrong about the valves though. I checked the workshop manual and I couldn't find anything about it there. But I seem to recall someone posted about it on Jims forum.

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Re: An Easter story on seals and camshafts

Postby Volker_P » Thu Apr 27, 2006 12:27 am

Hi Ibsen,
seems you are right about the valves. At least I found three more carbs without them. Would be interesting to hear what the non-european guys can tell to that item. Possibly they were only required if carb settings had to fulfill some regional smoke law or so.

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Ibsen
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Postby Ibsen » Thu Apr 27, 2006 7:08 am

According to the Clymer manual, or was it Haynes :roll: , the valve is there to prevent the engine from backfiring during decceleration:

And I found this descripton on the Cyclewareable.com website:

"AIR CUT OFF VALVES PREVENT "AFTER BURN" GENERATED WHEN THE THROTTLE IS SUDDENLY CLOSED.
WHEN THE THROTTLE IS SUDDENLY CLOSED, THE VALVE TEMPORARILY CLOSES THE SLOW-JET PASSAGEWAY---CREATING AN INSTANTLY RICHER MIXTURE AND THUS REDUCES "POP" SOUNDS UPON DE-ACCELERATION
."


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