Here we go with the start on the engine........
I know there are a lot of people on the forum that know these bikes inside out but I've written this bit in layman's terms so anyone who hasn't had one to pieces can understand it a bit easier.
This
is the whole point of the bike really, Honda flexing it's 1970's technical muscle. You all know if there is anything seriously wrong with it potentially there will be huge bills ahead
. Worst case scenario a new motor, which would need rebuilding as well, and then non matching numbers. I know someone in the UK who spent over £6,000 last year having the motor refurbished by a specialist.
I took a chance on the bike, maybe too big a chance, buying it unseen from Europe. Took a long time finding one but I chose this bike because it had low owners and low miles, even though it was a non-runner and I hadn't seen it, was it a good choice........Hmmmm, read on
I made a mild steel stand up so the engine would be easier to handle.
If you look at the front of the motor just under the head between pots 3 and 4 there is an oil stain, there are others and the bike is almost 40 years old so a few weeps are to be expected.
You can also see where I've started to clean the gasket faces on the exhaust ports, there are also a few exhaust studs that need replacing or helicoiling.
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I started to have a think about the oil on the front and why it was there.
The CBX, and the other CB's, use a dual chain drive for the cam timing. The crank drives the exhaust camshaft (A chain), and the exhaust drives the inlet camshaft (B chain).
The "A" tensioner and adjuster for the chain is at the rear of the motor, the "B" tensioner is at the top of the motor and adjuster for it is at the front.
This schematic shows the basic set up;
honda-cbx1000-supersport-1979-z.gif
All the following relates to the B chain, the numbers in bold relate to the schematic so it is easier to see what I'm on about........if anyone's interested in the technical bit
The locking washer (
18) for the "B" tensioner and the blanking cap (
17) seemed to be the source of the leak. There was a small hole in the blanking cap for the tensioner which wasn't supposed to be there? this can also be seen on the above engine picture.
I pulled the blanking cap out and looked up the hole, the locking bolt was visible.....but wasn't supposed to be
.
A lot of older bikes use a spring-loaded adjuster with a tapered rod (
6 and
8). Basically the chain wears, the locking bolt is loosened, the spring pulls the chain blade in which in turn moves the rod up a bit to tighten the cam chain and the bolt is nipped up a bit further down the taper on the rod. There are some pictures to follow which make it a bit clearer.
Because I could see the thread on the locking bolt it meant the tapered rod (
8) was too far down the hole and the bolt (
14) was actually
behind it, instead of resting on the taper....Time to take the cam cover off then.
Only six shoulder bolts to get the cam cover off, as you all know, it is imperative that the tachometer drive cap and shaft are removed first. If the shaft is left in it snaps the tacho guide off the top of the number six cam cap bearing. This is
very difficult to repair but no broken bits or damage on this one though :thumbup .
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There are plastic plates to hold oil in front of the inlet cam lobes, the two pipes are oil feeds to the cam bearings. While the cams were in I used the opportunity to make a note of all the valve clearances.
I had a think and the only reason I could come up with for the scenario I had was that someone had thought the top end was a bit noisy. Then either the knob of an owner (or more likely bigger knob of a mechanic) had deduced that it was cam chain, not bothering to investigate, they had removed the tensioner cap and shoved a screwdriver in there while the engine was running to "tension" the chain and make it quieter? WTF?
The big worry was the chain was that tight it had knackered all the cam bearings in the head........God knows why they had done something so stupid, if you don't know what you're doing why assume that you do, or worse still give it to a "mechanic" who
says he knows?
I'm only
assuming that it was a mechanic because, in their day, these engines were a bit daunting and expensive for an everyday owner? Anyway, rant over.
Left bank of the camshafts out, as you also know cams are made in four pieces and have a UJ in the middle of each for alignment purposes. These are called Oldham couplers, these "tick" on an old motor and you have to source oversize ones, but these were OK. The bearings in the head were all inspected and found only to have minimal wear marks so luckily no harm done by the cam chain cock up.
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Rest of the cams etc. out, you can see the witness marks on both ends of the the "B" tensioner blade where it has been rubbing on the chain.
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All the cams and caps out and on the bench for inspection.
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More bad news though........
The B tensioner clamping bolt had been sheared in the past, to get this out they had put a hacksaw slot in the bolt and head and wound it out. They had then Helicoiled it, presumably because they had made another balls of it and left the hacksaw slot in the cylinder head, which is why it was weeping oil.
Cleaned it as best as I could and put the AC TIG to work and welded the damage up, I dressed the weld off to form a new sealing face for the locking washer.
Also the B cam chain was found to be 2mm out of tolerance when stretched between the gears with a known tension on it. The chain is still available so a new one was put on order, the tensioner on the other hand was non stock from Honda
.
There are a few NOS places to get CBX parts from, one is Louis in the US. After exhausting all other avenues I emailed him but cost was very expensive for a tensioner blade.
I thought Honda would never make a specific part when they could get away with using a generic one? Wrong in this case, the 750's and 900's valves are different angles in the head which makes the "B" CCT shorter.
Onto plan B then, I bought a NOS 900F2 blade set from David Silvers in the UK and done some working out. The 900 blade was 16mm shorter OA than the CBX. I made a tool for pressing the rivets out and also a small extension piece to make the difference up. The old tapered adjusting rod was removed and a longer rod was manufactured with the same taper milled on, this was silver soldered onto the other end of the blade pivot.
Before the work - the knackered CBX one on the top and the NOS 900 underneath with no wear.
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The mount for the end of the 900 is also different so had to alter this;
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The replacement part, complete with spring, looks a lot more bent than it should be but when in situ the cam chain straightens it out. The new rod is 11mm longer than stock to make up for the shorter blade of the 900, you can also see the milled taper on the bottom of it.
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And fitted into the head, when the cams were put back the tensioner blade sat equally between the cogs with plenty of adjustment left and I'm sure it will work ok.
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Small point which could have ruined my day, you can see the 6mm cap head bolt that fastens the CCT into the head. In my wisdom I replaced the mild steel hex one with a stainless cap head.........then promptly dropped it into the motor. What a dickhead, the mild steel one could have been fished out with a magnet, if you found it. Obviously the stainless one can't so I spent a couple of hours searching down the cam chain tunnel with a dentists mirror on a long rod. Eventually found it resting on a casting having not dropped all the way to the crankshaft. I got a piece of 3mm welding filler rod and put a blob of adhesive on the end, then, doing my best impression of a consultant gynecologist (complete with sticky out tongue) I landed it on the bolt. Two hours later the adhesive had set and I pulled it out.
If I hadn't had got it out it could have meant completely stripping the motor down, lesson learned though.
As I've said, a lot of peeps on here will run rings round me on the technical stuff but I wanted to explain the engine problems I found as simply as possible so everyone could understand.