Cylinder head mounts...

M

motopsycho87

New member
So the recent bikes have no cylinder head mount. Any reason for this? It seems GG have stopped making the old heads, but the new ones with no mount are listed as fitting all models and thus supercede. I wonder why they've chose no mounts? Many older 2 strokes don't have them, but all new 2t offroad bikes do... Discuss :D
 
It could be one of two reasons. 1. To save weight or 2. If the frame flex's to much with a head stay it will break the cylinder at the studs. A lot of older Yamaha IT's had that problem so every one ditched the head stay to save cylinders.
 
It's pretty common for manufacturers to make changes to motor mounts to change the chassis handling characteristics.
 
So it begs the question, has anyone not used the head mount on a bike that originally had one? Notice any differences?
 
risk74 said:
So it begs the question, has anyone not used the head mount on a bike that originally had one? Notice any differences?
Click to expand...

I've considered it.. but haven't done it. I know some 10-11 models have snapped the upper mount on occasion, and I have read some speculation that the older chassis didn't flex as much as it could.. given that many report some harshness with 45mm Zokes and 48mm Sachs even once worked over. May see some benefits, or may see some added vibes. Maybe both.
 
That makes me nervous adding stress to the lower mounts. I figure some engineer, who is smarter than me, figured it was needed. But maybe they decided that it was one of those things that "we've always done" so they keep doing it. Without even checking if its needed. Obviously some engineer decided it wasn't needed.
 
Good points hadfield, and something that also should be considered. I'm no engineer either.

If I was going to remove them it would be for a test ride only.
 
In my opinion. It there to counteract the massive forces put on the engine cases and frame.
Think of the sprocket as a fulcrum point of a lever.You have the chain and sprocket trying to "lift" the front of the engine.The cylinder stays "hold" the engine down, so to speak.

The post '12 frames are much stronger. So, no stays needed.

Just my $0.05
I'm no engineer either.
 
I'm am engineer, but the amount of math required to find out how it affects the frame, handling, and vibrations would be enough to keep most occupied for a lifetime. If the aluminium plates were bracing the frame, they would snap rather quickly, but most find they only snap when other mounts are loose, or through fatigue caused by vibration. Older 2 strokes never had these mounts, and I've never heard of a chromoly frame saved by 2 spindly bits of aluminium. Personally I would rather have them there, more support points is better than less in my opinion. I would say they may be liable to braking due to expansion of the cylinder under heat, so would be better designed to accommodate flex. But history tells us they are not entirely necessary in many many bikes without top engine mounts. Probably just cost and weight saving.
 
motopsycho87 said:
I'm am engineer, but the amount of math required to find out how it affects the frame, handling, and vibrations would be enough to keep most occupied for a lifetime.
Click to expand...


Haha I'm not an engineer but I sell engineering services for a living. Sure if you had to do all the math by hand. But we do vibration analysis as well as stress testing in industrial applications. Could probably have the testing and analysis done in less than a month.

Pretty easy finding the resonant frequency. The big thing is having the right equipment.
 
With the right equipment and capable people, of course it can be figured out.

There are a ton of variables to consider, but if you had capable people with the free time to do it, and the equipment available to you to figure out materials, thicknesses, etc. then model it and do stress analysis, vibration, etc.....

I am an engineer and I have worked in several engineering environments and to be honest, I seriously doubt that half the people at GasGas knew why the head stay was removed. It could have have been lots of reasons. I also doubt that they did extensive testing to see if it could or should be removed. It is likely a design change that simply evolved to be. I do know that it accomplished several things though. It reduced cost, reduces complexity, reduced weight, and changed handling characteristics. I'm sure it also changed how the harmonics transferred to the the frame. It could be better, or worse.

I like that it's missing, just for one less thing to remove/install during maintenance.

Looking at GasGas's documentation in the manuals, and the way that bikes were fitted with different equipment seamingly at random, sort of forms the opinion for me, that GasGas may not know why the head stay is missing and probably couldn't find the documentation to explain how it happened anyway.

Luckily, I think that has changed with Torrot running the show now.
 
hadfield4wd said:
Haha I'm not an engineer but I sell engineering services for a living. Sure if you had to do all the math by hand. But we do vibration analysis as well as stress testing in industrial applications. Could probably have the testing and analysis done in less than a month.

Pretty easy finding the resonant frequency. The big thing is having the right equipment.
Click to expand...

I think you are both right. I'm not an ME but I know that vibration analysis alone could keep you busy for years if you wanted to understand everything about how all the parts of the assembly were reacting. But yes, if you were just looking for one or a few answers. Then yes with the equipment needed you could get your answers fairly quickly. Especially in this case, where it's a simple question of "head stay or no head stay".
 
Im no engineer either.
So my "vibration analysis"takes less then 15 minutes of ripping the bike through the woods.

As far as frequency, stresses and the rest of that.
If it breaks.Thats bad
If it doesnt break.Thats good.
 
gasgasxc said:
Im no engineer either.
So my "vibration analysis"takes less then 15 minutes of ripping the bike through the woods.

As far as frequency, stresses and the rest of that.
If it breaks.Thats bad
If it doesnt break.Thats good.
Click to expand...

Hahah! I guess what I was saying was a long winded way to say, we have probably discussed and analyzed it more than GasGas did.

Not that that's bad. I've enjoyed the discussion and like seeing people's theory's.
 
motopsycho87 said:
I'm am engineer, but the amount of math required to find out how it affects the frame, handling, and vibrations would be enough to keep most occupied for a lifetime. If the aluminium plates were bracing the frame, they would snap rather quickly, but most find they only snap when other mounts are loose, or through fatigue caused by vibration. Older 2 strokes never had these mounts, and I've never heard of a chromoly frame saved by 2 spindly bits of aluminium. Personally I would rather have them there, more support points is better than less in my opinion. I would say they may be liable to braking due to expansion of the cylinder under heat, so would be better designed to accommodate flex. But history tells us they are not entirely necessary in many many bikes without top engine mounts. Probably just cost and weight saving.
Click to expand...

I can't recall if my old 2 strokes had head stays or not, but I still have a 1980 VF 414F Montesa mx'er that I bought NIB in March '81 and it has a head stay. It's aluminum but pretty hefty.

I don't plan on running my 200 XC without one.

RB
 
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