Cams, cam chains, tensioners, springs, and bearings (camshaft musings, pt 4)

Tips and Recommendations from Guru Mike Nixon

Moderator: Whiskerfish

Post Reply
User avatar
mikenixon
Early 'Wing Guru
Early 'Wing Guru
Posts: 997
Joined: Thu Dec 10, 2009 1:51 am
Location: Prescott, AZ
Contact:

Cams, cam chains, tensioners, springs, and bearings (camshaft musings, pt 4)

#1

Post by mikenixon »

There is a tendancy for folks to think they know more about cams than they really do. Did you know for example that Honda once made cams with angled lobes that made the valves rotate and thus clean themselves of carbon? A good idea but they had to stop because customers complained of knocking noises in the cylinder head. The cams were banging against their bearings from the lateral thrust the angles created. (A smart factory Honda tech rep proved it by pushing on the ends of the cams while the engine was running.)

Cam wear
With rare exception, Japanese cams are made of surprisingly soft, easily-drilled cast metal and wear at a constant, fast rate. By 10,000 miles the cam is considerably worn, and valve timing thus appreciably shortened. I have perked up many an engine simply by ordering replacement cams made to stock specs (new cams from Honda are long gone), which sufficiently and happily restored good valve timing. For the few engines where that isn't feasible, I have found that advancing the cam a couple degrees can also help recover the factory valve timing lost to wear and brighten engine performance. 1

Certain models of Japanese bikes have much more than the normal amount of cam wear, actually severe damage, galling, tearing, of their cams. Many are unaware that Honda made/makes rocker arms whose required surface hardening consists merely of chrome plating. This unfortunate expedient has resulted, in many instances, in the chrome failing and the rocker arm then becoming a cheese grater and taking out the cam. The effect is mild on some engines, worse in others. One set of the really bad bikes to look out for are any with the four-valve Kawasaki ZX900 series engine, including the early 80s 900 Ninja, Concours 1000, and the 900 Eliminator. In addition, certain Honda models, namely all the early 1980s first-gen Honda V4s, 700cc and larger. These two engine types have the same two things in common: chromed tandem rocker arms whose four valve springs exert unusually high pressure on the one cam lobe, combined with (for the period) unusually high valve lift. This combination results in serious cam deterioration due to the follower's chrome eventually peeling due to the extreme pressure. 2

Valve springs and things
Honda valve springs are known among veteran mechanics as the best in the industry. Almost without exception, aftermarket springs do not offer any improvement. Whether resurrecting bikes that have sat for years, or racing vintage Hondas, the stock springs have proven their worth. Honda's valve guide seals were once equally famous; mechanics used to put Gold Wing seals on Kawasaki Z1s. And the cast iron guides found in Big Four engines are worlds better than the non-ferrous guides some racers use. They use them because they are more readily available, they ream easier, and theoretically they add cooling to the valves. They're a poor choice outside of racing however.

I'm always surprised when I find valve adjusting locknuts only gently snugged. This is risky. The velocities that the ends of the rocker arms reach are astronomical. That tiny locknut can and has rocketted right through a quarter-inch thick cast aluminum valve cover, leaving behind a gaping two-inch diameter hole (see the image below). For one model prone to this Honda even issued a special extra-long tightening wrench. But overtightening isn't a good thing either. Though the adjusting screws are hardened, their threads go bad from overtightening of the locknuts, which then makes adjusting clearances an aggravation as the screw insists on finding its same place every time until the screw is replaced.

Cam bearings
Honda cams are fitted to their bearings very loosely, typically 0.005" or more. Yet noise due to this looseness is rare, and affects only one Honda model that I can think of. It's just the way they're made. Some tuners, including yours truly, have in special cases reduced this clearance through machining, for performance or noise reasons. The bearings are of course cast aluminum, which has never posed a problem because the Japanese aluminum alloys employed are extremely durable, and also due to copious oiling. I have seen steel cam journals wear more than their aluminum bearings. And, interestingly, Honda actually used an aluminum cam in one of their lawnmowers. *That* is a very trick application of technology.

It's common for folks to overtighten cam bearings. Part of the blame lies with oddly consistent errors in many OEM manuals. At least one Asian manufacturer's U.S. office has issued warnings intended to override their official specs. Honda's listing of 12 ft-pounds for cam bearing bolts is grossly in error, on at least two important fronts. First, a ft-lb torque wrench is never used on 6mm bolts because the setting on the tool is too low to be accurate for such a critical measurement. Second, those bolts should never be tightened more than 90 inch-pounds, which is little more than *half* that 12 ft-pound book spec. There is quite a lot of backstory to all of this, involving service bulletins, warrantied engine failures, and more. Suffice to say, the forums are completely ignorant of this and as with so many things make a complete mess of the issue, promoting as they do higher tensile cam bearing bolts than stock. This brings us to torque wrenches. If you are messing with Honda engines and don't own a an inch-pound torque wrench, shame on you! 3

Cam design
Cams made for rocker arm engines have oddly assymetrical lobes. This is due to the contact point on the curved pad of the rocker arm changing as the cam is rotated. The cam's unequal lobe shape compensates for the rocker arm system's inevitable geometry change as the valve moves. Note the really peculiar shapes of the cams in Honda's 1970s DOHC CB450.

A lifetime around camshafts gives one an intuition as to what makes an ideal cam lobe shape. Smokey Yunick proved it, as have others, and so have I. Like many, I once ground my own cam using a makeshift apparatus. The subject bike suddenly made enough extra power to cause the clutch to start slipping. V-blocks and "eyeballing", that's all it took. But don't try this at home, kids. 4

Cam chains
Hyvo type cam chains replaced roller cam chains on Honda's bikes in the late 70s. Hyvo, for "high velocity", is a trademarked name; the generic term is link-plate chain, gear chain or silent chain, the last rather ironic inasmuch as in motorcycles they can be noisier than roller chain when out of adjustment. And adjustment is problematic. The increased mass of the Hyvo chain over its roller counterpart, and its unfortunate application outside its original design parameters (wherein, in cars, they were centrifugally self-tensioned), makes for very creative approaches for pursuading it into tension in motorcycles. 5 It also wears surprisingly quickly, the chain's mass and tortuous encasement doubtless adding to this, resulting in a chain that is significantly worn by 30,000 miles, and whose cam's timing is then markedly retarded (delayed), softening engine performance. Worse, many of the Hyvo cam chains originating in older Hondas are now discontinued as replacement parts. Worse still, Honda is being unconscionably deceptive about this and is putting inferior third-party (aftermarket) cam chains in wrappers with their names on them, just as they are also with ignition points and other vintage parts. I laud them for addressing vintage. I am scandalized that they are doing so in such a disengenuous, lowest-common-denominator fashion. 6

Something not many are aware of is that the cam chain is the highest wearing part in the bottom end of the engine. Yes, more than the clutch and more than the many bearings. Where this becomes evident is when the crankcase gets dirt in it. Dirt entry makes the engine oil abrasive. This came to be known many years ago when four-stroke dirt bike engines started appearing with odd and contradictory test results: low cylinder compression but good (low) cylinder leakdown. This odd but now-classic presentation is always cam-related. Either the cam lobes are heavily worn, or the cam is out of time due to severe cam chain wear, with the tensioner being fully deployed the important red flag. While dirt is liable to get into an engine through various means, a number of these engines had air filter issues. Either the filter was improperly serviced and maintained, or it was an aftermarket type that filtered very poorly. The resulting entry of contaminants ended up in the crankcase. 7

Cam chain tensioners are a problem in vintage powersports. One problem is that owners of 70s Hondas seem to not easily learn that their bike's cam chain tensioners are entirely manually adjusted. Despite spring assistance, properly deploying them is a manual, several step, specific procedure proposition, and even the official manuals often leave one in the dark. Another problem is these same folks seem to almost universally deduce that Honda cam chain tensioners' bolts are for tensioning when in reality they are merely lockbolts. Folks are breaking off these bolts inside the engines' crankcases as we speak. A third problem is the rack and pinion design of many of Honda's 70s cam chain tensioners. The gears are made of sheet metal, with teeth that are stamped not cut, and after almost 50 years now typically rust-frozen, thus requiring even more manual and unintuitive manipulation than even when new. If you know these issues, the parts work fine. But they are demanding of this knowledge.

Of course, the four-cylinder Wing has its unique skateboard wheel like cam belt tensioners. I'm sure you know these are fully manual, but of course are spring-loaded to exert moderate pressure when activated. They're a bit troublesome too. Get them too loose and ignition timing isn't its best; too tight and they squeal, warning of impending failure. Actually a rather flimsy design but adequate if treated carefully.

Cam timing
Many seem to stress over cam timing, assuming that Honda made the marks to line up perfectly. They didn't and they don't. Add to this the aforementioned cam chain wear issue and newcomers to the task can be challenged. Mechanics learn to judge correct timing by noting whether a sprocket tooth's roughly 15 degree difference is closer or farther relative to the mark. It becomes even trickier in many engines because as the cam bearings are tightened, the cam rotates slightly. Judging its final position takes a little skill. The shim-under-bucket engines common for many years demand camshaft removal to adjust valve clearances. Thus cam timing is now a maintenance proedure and not simply something done only during a rebuild.

The four-cylinder Gold Wings have very large valves set in fairly widely-spaced semi-hemispherical combustion chambers. Big valves set at sharply opposing angles, in other words. Thus, tangling of valve with valve or valve with piston is potentially easy if cam timing gets off. In fact in my experience it is inevitable. 8

Next post, Cylinder compression and related

1 Aftermarket cam manufacturers are experiencing a renaissance of stock-spec cam orders.

2 This syndrome has no connection with lubrication, despite many insisting otherwise.

3 Seriously. Like a compression tester, an inch-pound torque wrench is mandatory if you take an active role in maintenance.

4 The difficulty with doing this is the cam's lobes must be restored to their original mirror finish or the rocker arms or followers will be affected negatively.

5 The automotive-derived hyvo cam chain is centrifugally self-tensioned in its original application in cars. In motorcycles, tensioners push on it and require it to be snaked through bends and angles it was not designed for, and this coupled with the chain's mass conspire to wear it prematurely. Even faster than the older roller type chains in my view.

6 Honda has gone third-party with a lot of vintage parts sourcing.

7 The K&N gauze type air filter is over-represented here.

8 Mistiming the cams in a four-cylinder Wing will not make your day. Like virtually all motorcycles, the engine is what some call an "interference" type, meaning the valves will tangle with the pistons if cam timing is not correct.

Image
User avatar
sgwilly
Gold Member
Gold Member
Posts: 1029
Joined: Thu Apr 26, 2007 6:43 pm
Location: Clayton, NC

Re: Cams, cam chains, tensioners, springs, and bearings (camshaft musings, pt 4)

#2

Post by sgwilly »

I missed this one when it came out. Great info. Over the years, I've messed with several of the engine designs you described. I particularly remember working on a Honda DOHC 750 and thinking, "this timing chain tensioner bolt doesn't do anything!". It's a miracle I didn't snap it off.
User avatar
desertrefugee
SUPER BIKER!!!!
SUPER BIKER!!!!
Posts: 3947
Joined: Fri Nov 11, 2011 9:33 pm
Location: Chandler, AZ, USA

Re: Cams, cam chains, tensioners, springs, and bearings (camshaft musings, pt 4)

#4

Post by desertrefugee »

Extraordinary Mike. Extraordinary. Once again, thank you for sharing. Your contributions here are invaluable and should be broadcast far and wide. I can't think of any other author who's offered up (or is capable of doing so) such a broad swath of insight into the inner workings of these vintage machines. I know, personally, I am compiling it offline. All of it. Thanks again.
User avatar
mikenixon
Early 'Wing Guru
Early 'Wing Guru
Posts: 997
Joined: Thu Dec 10, 2009 1:51 am
Location: Prescott, AZ
Contact:

Re: Cams, cam chains, tensioners, springs, and bearings (camshaft musings, pt 4)

#5

Post by mikenixon »

desertrefugee wrote:Extraordinary Mike. Extraordinary. Once again, thank you for sharing. Your contributions here are invaluable and should be broadcast far and wide. I can't think of any other author who's offered up (or is capable of doing so) such a broad swath of insight into the inner workings of these vintage machines. I know, personally, I am compiling it offline. All of it. Thanks again.
Too kind. Good to hear from you.
User avatar
mikenixon
Early 'Wing Guru
Early 'Wing Guru
Posts: 997
Joined: Thu Dec 10, 2009 1:51 am
Location: Prescott, AZ
Contact:

Re: Cams, cam chains, tensioners, springs, and bearings (camshaft musings, pt 4)

#6

Post by mikenixon »

sgwilly wrote:I missed this one when it came out. Great info. Over the years, I've messed with several of the engine designs you described. I particularly remember working on a Honda DOHC 750 and thinking, "this timing chain tensioner bolt doesn't do anything!". It's a miracle I didn't snap it off.
LOL!
Post Reply
  • Similar Topics
    Replies
    Views
    Last post

Return to “Mike Nixon's Spot”