Long Forgotten ’81 Pro-Link Resurrection

[shiskowd]

Now that winter is beginning to settle in a few of our locals I thought I’d start a thread on a project that I’ve delayed for a while. For your viewing pleasure – don’t hesitate to suggest, correct, ridicule, or otherwise weigh in on this journey. This will be a slow burn – between my work, family (1st grandchild expected in the next weeks) and other commitments this will stretch many months, years(?).

I dragged this bike home a year ago, trading some carb work for the bike from a local CBX hoarder who had acquired the bike as part of a large lot sale of bikes & parts a decade + ago. Bike had last run 24 summers ago before a catastrophic failure had pushed it to the back of various sheds since. No history on the bike other than some legend it was once in the stable of a bike gang of angelic fame. The bike is mostly there, some bits clearly removed/torn off while it was running and/or cannibalized since the failure.

You’re likely wondering why I’d take on such a dumpster fire. I’ll explain in later posts…

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[NobleHops]

It’s got bones!

Looking forward to pitching in on the resurrection.

[steve murdoch icoa #5322]

Certainly be following along.
Looks like Ontario Moto Tech exhaust.

[daves79x]

Do you have a set of cases for it?

Dave

[Larry Zimmer]

This one WILL be a project. If your 'barn' is heated, good things for the long Winter months. Have fun. And, certainly ask anything/everything here. All are more than happy to help.

[shiskowd]

Two years earlier I started my first CBX restoration viewtopic.php?f=102&t=11699 that had a very good outcome in my opinion thanks in part to the feedback/direction I received from many on this site. For that project I started with a largely intact early ‘Z ‘A’ bike with most of the bones and a ‘B’ parts bike that had little more than an engine, frame and wheels. Turns out both engines were in fine shape outside of a needing new set of pistons, cylinder rebore, valves and the regular gaskets/seals. I ended up using the ‘B’ frame and engine cases/crank with the ‘A’ bike parts for the rest of the restore.

I still have the ‘A’ engine cases /crank and all the other ‘B’ components for a complete engine. All the bearing clearances in the head, crank and rods are within spec so outside of the spendy pistons, cyl rebore and valves I have an engine looking for a home.

Enter the dumpster fire ’81 pro-link. I knew it had a bust engine and had been robbed of some of the pro-link specific bits but it had the bones to create a naked pro-link, potentially a nice addition to round out my restore ‘Z and the ’82 pro-link that I woke up last year viewtopic.php?f=102&t=12140.

Last fall I began to strip the bike, noting the condition and what was missing. I find stripping a bike to be quite satisfying – speculating how well the bike was maintained, counting the number of non-OEM fasteners that found their way on the bike over the years, hack repair jobs, etc.

The burning question – what caused the #1 connecting rod to fail and cut off the left side of the engine case…

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[daves79x]

Far and away the most likely cause of the case disaster was a hydro-lock. The rod bearing could have failed/seized as well, but far less likely.

Dave

[CBX-tras]

My opinion:

It's either a bearing/oil failure or hydro lock. But, I'll go with the bearing failure. Here's why I say that:

Hydro lock is less likely with the '81 due to the AVF (if working) and when it does happen it usually bends the rod on startup and prevents the motor from turning another revolution. (No case damage, usually).

With the mileage on this example, if oil changes were neglected or even if they weren't, crud will accumulate in the crank throws and eventually block oil from lubricating the rod bearing and the excess splash to lubricate the cylinder walls and the wrist pin.
At road speed, there would be enough momentum to rotate the crank several times before it separates and does case damage.

That's my theory. Disassembly with a good CSI will show what really happened.

[shiskowd]

I had assumed that the failure was a hydro-lock, even on the post '79 models with the auto fuel valve and the separated routing of the carb overflow drains that were to lessen this outcome. But I believe this was not the case when I disassembled the engine.

Removing the valve cover I discovered the #1 & #2 camshaft bearing caps bolts were not only loose but in the case of #1 cap, they were a full 4 turns out from mating with the cap. #2 cap was about 2 turns, #3 & #4 were torqued appropriately.

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Removing the left exhaust camshaft revealed the camshaft and all bearing journals in that part of head were damaged. The buckets over #1 cylinder were discoloured, things got very hot up top before the rod let go.

Pulled the head to find the remaining carnage.

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I suspect one of the exhaust valves had burned as it wasn't seating causing the overheating that snowballed into the top of the piston melting, piston seizing, rod breaking, then sawing through the engine case.

Here's some further details. The exhaust valve shims were all in the range of what I believe these bikes were typically shipped (generally 2.75 to 2.90 mm) which seemed generous for a bike with 66,000 km's. When I disassembled the valves in the head I found all the exhaust valves had been 'tipped' - the normally chamfered valve stem ends had a very sharp edge. In some cases they were tipped so much that the valve stem did not extend past the collets so the bucket was mating not to the valve stem but the collets (hoping you can visualize this).

The head of course needed to be removed for the exhaust valves to be tipped so there was opportunity for #1 & #2 cam cap to not be torqued down, causing them to loosen over time resulting in the camshaft flexing messing with the valve clearance and the valves not opening sufficiently, which could have resulted in a burnt exhaust valve.

The head is scrap, the cylinders would be fine with a new sleeve inserted in #1 and a rebore in all. The balance of the engine looks like it should with 66,000 km's on the clock. The precious cam chain tensioners look great with little wear or cracking. I had the crankshaft inspected by a professional mechanic - it's all within spec, even the rod journal for #1 (the softer bearing took the beating).

For the more experienced to speculate with me, did the cam cap bolts loosen due to the hammering in cylinder #1 as the carnage unfolded or were those bolts simply not torqued during the last time the motor was disassembled??

[tevan]

It looks like to me you have a scrap motor. You are going to have a bunch of $$$$$ in this engine. I would find another used engine and go from there. Good luck

[NobleHops]

What Terry said. Don’t start there, there are better donors to put your time and effort into.

[JoeInTUS]

I still have the ‘A’ engine cases /crank and all the other ‘B’ components for a complete engine. All the bearing clearances in the head, crank and rods are within spec so outside of the spendy pistons, cyl rebore and valves I have an engine looking for a home.

[shiskowd]

Thanks Joe - yes, I have a complete 'Z engine but given the condition of the balance of this '81 engine I'm wanting to use the clutch and primary shaft from the later engine in the 'Z cases. Will take a close look at which transmission, oil pump, etc. to select from the two engines.

As for the balance of the bike, while the '81 didn't show too well, the components on that bike are in decent shape. The bike must have been stored inside all these years as there is no rust or corrosion under all the grime. The fuel tank has a couple small dents but was properly drained - no rust internally. I rebuilt the carbs last winter - of 5 sets that I've revived this set was the cleanest internally. The bike last ran with ridiculous amounts of chain lube, absolute mess to clean up but provided additional rust proofing on the back half of the bike.

The front end of the bike was harvested of the larger forks, better brakes, etc. and swapped out with a set from 'Z. I found a complete low mileage '81 front end from a custom builder in Ontario for a great price that replaces everything missing. I've collected various other pieces that are missing from the engine (alternator) and chassis (side covers). I have a set of Euro Pro-Link foot peg mounts and have a line on a set of Euro low bars for those forks to create a more sporting riding position.

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[CBX-tras]

From what I can see in the photos, it appears to be oil related failure.

See how dark the remaining oil is? Low or little oil, lost it's lubricity, got very hot (as mentioned) and POP goes the weasel.

By the amount of carbon buildup too, tells me this bike was rode hard and put away wet. In other words, routine service neglected.

[shiskowd]

From what I can see in the photos, it appears to be oil related failure.

You're likely correct but would those cam cap bolts loosen like that with that sort of failure?

The frame is prepped to go for sandblasting and powder coating.

On to the engine (from the '79). I found a slightly used Neway valve seat cutter tool set last winter and I thought I'd try my hand at cleaning up the seats. The intakes look real good, the exhaust seats have some slight pitting. I found there are two exhaust valve guides where the cutter pilot guide doesn't seat into the valve guide snuggly which per the Neway manual suggests the guides need replacing. When I insert a new exhaust valve there is some side to side movement on those two guides.

The previous owner of the Neway kit included one new NOS valve guide and the Honda reamer tool. I don't have the valve guide remover tool but I see they're readily available. The manual suggests heating the head to 300F before punching out the old guide and installing the new one.

Is this best left to someone whose familiar with this procedure?

Do I really need to be concerned about the two valve guides?

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