How is the lining added to the cam chain tensioner blade

Hey Red, I've been thinking about this, and I suspect the blade breakages in your race engines might be a combination of several factors.

Given that breakages in normal engines are rare, looking at the differences between your race engine and a normal triple engine seems a good place to start.

The 9500 rev limit doesn't seem to be hugely in excess of what you could see in a street engine, so I would hazard a guess that it's not chain speed that's doing the damage.

I guess the load on the cam chain in your engine is greater than a road bike because of higher lift cams and/or stronger valve springs. I don't suppose there's much you can do about that if those things are necessary for the performance you need. The tensioner is on the unloaded side of the chain anyway, so I can't see the load being a big contributor to blade failures, unless there's some weird dynamic effect between the tight and loose sides of the chain run.

Running closer shaft centres would make a significant difference to the picture because of the greater slack in the chain. I think you're on the right track with the loss of camshaft height leading to excessive bending of the tensioned blade. A small change in shaft centre distance can make a large deflection in the chain run. It would be interesting to draw it up in CAD to see how far the thing has to bend with reduced shaft centre distance. I might be able to plot a curve of tensioner strain vs camshaft height.

A couple of people suggested shortening the cam chain to compensate for loss of height. I'd be surprised if that is a viable option because even taking one link out (necessitating an offset joiner link) would shorten the chain by 3/8" (9.5mm). So you'd need to drop the about camshafts by about 5mm for it to fit. I dunno whether you can accommodate that sort of change in camshaft height with the bearing blocks and valve drive components. I'm imagining cam lobes interfering with the valve bucket recesses.

I guess you can keep jacking up the camshafts by making taller bearing blocks, or putting shims under the blocks. Your 1mm offset cam blocks may mitigate the problem, but again, I dunno how far you can lift the cam bearing blocks before you run into difficulties with valve shim thickness or clearance under the cam cover.

I also agree with the suggestion that the roller wheel on the back of the tensioner blade is a poor design. The thing doesn't need to roll, so the roller wheel is a strange design choice. That makes me wonder if they started with roller type tensioner and then added the blade as an afterthought. This raises the possibility of getting rid of the blade altogether and simply using a rubber roller or steel sprocket fitted to the tensioner (something better than the crappy plastic wheel anyway). Many engines just run rollers or sprockets as tensioners without blades (Laverda 750 twins for example). But maybe that could create other problems associated with chain harmonics. Only way to find out is to try it, but it could be an expensive experiment.

The tensioner roller is a single point contact that doesn't offer any support to the blade itself. If you could ditch the roller and make up a shoe with a more sympathetic size and shape to the curve in the blade, I'm sure it would make life easier for the blade. A CAD representation of the bend would be helpful to determine a suitable shape.

Making stronger tensioner blades would certainly be a useful thing to do, and probably has the best chance of fixing the issue straight off. But I don't suppose it would be a simple solution with the R&D work to come up with a design and then find someone who can make them for a sensible price.

One thing nobody has suggested (probably because it's a dumb idea) is to ditch the chain altogether and use a toothed belt. That would also have the advantage of being less power hungry, so it might liberate another couple of horsepower to the rear wheel. Continental (the tyre mob) makes belts that will run in the engine oil. I presume there are other manufacturers making oil tolerant belts too. If you can find a belt of suitable length and width to fit the engine dimensions, you'd just need to source the toothed wheels. Easier said than done as far as the crankshaft end is concerned. It shouldn't be difficult to fit a belt wheel to the tensioner assembly.

Good luck sorting the problem. It's a tricky one.
 
I think it is breaking because the cam chain is beating it to death. Not a problem I would think with the tensioner having a destructive harmonic frequency because it is not moving all by itself, but because the cam chain is making it move. Why is the chain not breaking if it is beating the tensioner this hard? If this is the case, I don't think a stronger tensioner is gonna help.

Now is the problem because the motor is spinning up to 9500 RPM or was the problem there at lower RPM's but beacause most of us don't reach redline when on the street?

If it were me, I would consider putting a strain gauge on the cam chain adjuster to see what is happening when it breaks. This will show you at what RPM's the chain starts to beat on the tensioner.

Also, is there evidence of the adjuster pin having moved out when it fails? If it is beating the tensioner this hard I would think it would move?

Anyway my thoughts after too much bourbon and time for bed.
 
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It's been several years since i had a triple apart so I'm going from memory on dimensions of the tunnels.
But
There's a couple of Kiwis making a replacement tensioner/guide setup for the big 16V air cooled Hondas. They are an absolute dogs breakfast design as standard. One chain goes crank/inlet cam, another goes between the cams. The long run at the back breaks tensioners and guides. As stock they are the usual metal/bonded rubber.
These guys provide a moulded guide for the front and another moulded piece as the tensioner - which they pivot off the top.
It's a deep section moulded plastic/nylon, black in colour, capable of handling wear and heat. The Honda chain is a Morse which is only relevant because it's heavier than the Laverda roller.
The deep section - about 30mm at the deepest point - gives stiffness and the chain contact edge is profiled to match the chain curvature. Tension is adjusted via an 8mm screw at the back of the barrel

These tensioners and guides are very strong and stiff. Also light. But to do something similar would require room in the chain tunnels.
Without one here to look at I don't know if these could be enlarged by machining without weakening the barrel too much

Red - there's a mob in Queensland racing those Hondas who I believe carry the tensioner/guide kit. Might be worth going and having a look.
Memory's kicked in - Rex Wolfenden.
The bonus of using an all "plastic" blade is of course, no metal pieces in the motor - if it ever broke.
 
Not much space to work in on the triples, any deviation from stock is going to cause a lot of head-scratching...

Imho, the tensioner roller is there to provide a "soft" contact point to the blade. Liquid-cooled Zane 750 models have a rigid, squared-off bolt as tensioner device that bears against a similar blade, these bikes show a stupid consistancy of blade breakages around the point of contact between tensioner bolt and blade, despite them being supported at the lower end. Only one edge of the big, fat bolt (M16 iIrc) has contact with the blade. Once the edges of the bolt are rounded off, the breakages go away. These breakages did not happen on the 500-derived 650 and 668 models. The chain run is slightly longer on the 750s due to the narrower cam spacing and 2 extra links.

The sheer length of the chain run requires a slipper-type tensioner, imo a roller in the middle would let the 2 shorter runs flap around too much. Running the chain a little tighter might reduce the amount of chain flap enough to let the blade survive. Or maybe convert to a spring-loaded system istead of the rigid tensioner screw. Not too difficult to incorporate a spring into the stock tensioner set-up.

piet
 
Is the use of a central guide roller a la SF/Cs a useful suggestion? Or even a possibility? On the SF motor it's a large dia nylon wheel. If used in the triple it may reduce the length of free chain that can subsequently 'flap' and cause the breakages.
 
All valid points, but if I’m not mistaken, the force on the blade is greatest not while accelerating or under forward load but the off button factor. At those compression ratios backing of is like activating an engine brake.

Time to explore a slipper clutch.
 
If you ever see a high-speed video of a chain, they do some crazy unexpected movements, good point Chris about shock waves.
 
Does the cam chain actually reverse it's load when you shut the throttle? I would have thought that it is always dragging the cams against the resistance of the valve springs even as the crankshaft increases or decreases speed.
 
One of the problems - maybe the biggest - is the uneven loading on the chain in a 180 triple. It's possible that is setting up waves in the chain at certain speeds which aren't there at others.
Historically the damping of standing waves in high speed chain drives has been the problem. Usually solved by guides which constrain the chain to follow a desired curve. If the guide isn't stiff enough to do this over the rev range required, then something will break.
This asssumes the loadings are close to or are symmetrical - pull, pause, pull, pause - as they meet loads from the cam lobes evenly spaced around an engine rotation.
But the 180 triple has unevenly spaced load peaks. So standing waves probably aren't the cause. I'd pick that it's the load peak occuring after the long pause that's doing the damage.

Bear in mind here that the cams don't march in lockstep with the crank. They'll have a tight chain going up a lobe - and spring pressure will tend to slacken the chain as it comes down the lobe. So they aren't a constant speed.
In the angular distance which would be occupied by a 4th cylinder, the cams are not loading the chain to any great extent, simply being turned without any valve activity. So point of maximum slack....Then when the next lobe appears, bang straight to maximum load.

There are methods existing to dampen - or limit - cam movement relative to the crank as in gear drives for instance this sort of thing gets very noisy. Most involve some form of cam brake or friction device to make the load as constant as possible. Not really suitable for what's wanted here.

So what is wanted ? Well. IMO, as long as possible tensioner slipper and guide runs. The longer the run on these the less the point load is which should reduce the chances of them breaking. The tensioner blade needs to be curved to the desired chain curvature - and stiff. Very stiff.
It also does not need to be rubber or plastic faced. Plenty of chain tensioners in history running a hardened steel face against a chain. Just put a magnet in the sump.

Plenty to think about over a beer or two.
 
twinweb said:
this is off gsx 1100-2 guides i know -but spring loaded tensioner
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One guide, one tensioner blade - and the spring loaded tensioners fail. I've built rather a lot of GSX/GSXR race engines and the first thing which goes on is a manual tensioner. The tensioner blade on these breaks above the point where the spring loaded plunger meets it. Usually with big cams and too stiff springs.
If anyone really wants to try a spring loaded tensioner, use the Yamaha ratchet style. They don't give way under load.
 
I think you're on the money with the uneven tension sequence of the 180, Greg. Combine that with the high lobes and stiff springs red uses to obtain safe 9500rpm and the forces are going to be a lot more considerable than in a stock 180.

When i rephased the SFC crank to 270 I had concerns about this very thing, introducing a 'slack' phase into the cam sequence. Fortunately with a duplex chain and a twin roller guide and tensioner system (and a redline around 8000) no issues eventuated.

Sounds to me like a VERY strong tensioner blade might be the key for Red.
 
Thought from left field. How about bonding two blades together with the plastic surface removed from the non-contact one. Using a layer of bonding material between them to act as a dampening medium. A lot of equipment resilient mounts in the navy are made in a similar way.
Just a thought.
 
chrisk said:
All valid points, but if I’m not mistaken, the force on the blade is greatest not while accelerating or under forward load but the off button factor. At those compression ratios backing of is like activating an engine brake.
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Sorry Chris. You are mistaken, or at least confused. Cam chain load has nothing to do with engine load. As far as the cam chain is concerned, there's no off button factor or any kind of engine brake scenario. The cam chain never operates in an overrun mode with the camshafts driving the crank. The crank always drives the camshafts. Whether the bike is at full throttle or closed throttle makes bugger all difference. The cam chain is still driving the same way.

A slipper clutch won't make any difference to cam chain load.
 
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GregT might be onto something. I was thinking about the uneven firing order of a 180 triple before, and wondering if failures of the tensioner blade are more common in 180° engines than in 120° engines that have an even distribution of load impulses. But probably not. I guess breakages aren't frequent enough to make a statistically valid conclusion.

But it made me think about impact loads. The highest load on a cam drive system is when it has to open the exhaust valve against the cylinder pressure that's holding it closed. The cam follower must be like a hammer hitting the cam lobe, which would put a sharp shock load on the chain for a degree or two of its rotation. The hammer blows probably increase with engine power output because the residual pressure in the cylinder would be higher. I don't know whether these shock loads are somehow transmitted to the slack side of the chain, but I suppose it's not impossible.
I wonder if some kind of cush drive on the exhaust cam sprocket would make life easier for the drive system. A degree or so of rubbery movement between the shaft and sprocket isn't going to affect cam timing enough to worry about.

We need an engine design specialist. I'm surprised Julian hasn't chimed in.
 
I am wondering if making the chain adjuster hydraulic might help? It will tend to dampen any harmonics. But the problem is on a triple you have no oil pressure to play with.

Now this will be considered heresy but................................. if the engine were a 120 would it be breaking tensioners?:eek:
 
redax5 said:
so assembled an engine sort off with top case, barrels, head and bolted in a new cam chain blade and rolled it over to see where it sticks out
Not seeing how I can make a lower support, if I was maybe using standard engine studs I may be able to drill and tap in below the engine stud and screw in a retaining bar but our engine case studs are 10mm x 65mm long in the threaded section so they foul any chance of getting a threaded hole in position
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How about a folded steel retainer clip that bolts onto the inside of the crankcase? (something like my little sketch below).
Or if you don't want a bolt hole through the upper case (potential oil leak), maybe something of a similar nature that bolts onto the bearing web next to it. For ease of assembly, it needs to be something like a slot or pocket that that you can poke the bottom end of the blade into from above. It needs to be deep enough to stop the blade popping out when it's at full bend. If it could stop the blade moving sideways as well as forward/back, that would add another degree of control. It could be sideways movement that's doing the damage. Who knows?

I see that there are quite a few dings and scratches on the inside of the crankcase where it's been attacked by bits of busted off tensioner blade. I'm not drawing any conclusions as to failure mode from that. It's just interesting.

cam tensioner blade lower support.jpg
 
Have a look at the Suzuki parts diagram. The front guide plugs into a pocket which bolts to the lower case half. The tensioner blade is pivoted off a bracket which bolts in to the top surface of the top case.
A bottom pivoted tensioner could have it's pivot point recessed into either the bottom of the barrel or the top of the top case.
The front guide could be made full length by locating the bottom anchor point in an extended "case guard" or whatever the bolt in pillar is called that goes in from the outside of the lower case.
 
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