Topic: 750 internal case saver

[Don R]

Does anyone use the steel chain shield that fits into the sprocket area? My brother put one on his bike when it was new in 74 but I haven't seen another one. Were they effective in protecting the crankcase from a broken chain? If so I'm thinking of making one for my bike and maybe a few more.

[mick7504]

I've always liked having one of those.
Seen the results first hand of a chain letting go and it's not a pretty sight.
Got a brand new one now that I got on Ebay and they come along from time to time.
Part number on the bag is 11353 300 010 but no longer available.

[Don R]

Thanks Mick!

[MCRider]

I was in Honda shops in the heyday of breaking cases. We warranteed many, many cases. The case protector was an "OMG what do we do now" response from Honda. Are they actually available or is this NOS. I'm really surprised to see any around. And the fact that they aren't already installed should tell the tale.

They are not needed, and no I've never seen the results of a broken chain on a bike that had one. They were a band aid on a cut that was or has already healed.

A Cb750 with a modern chain (and a properly routed battery tube, maybe) has nothing to fear from broken chains. Many many bikes with chains have much more horsepower than our beloved CB750s and broken chains just don't happen.

I wouldn't tell someone not to put it on...I'm just saying...

[mick7504]

Hi Ron

I've got 2 of these NOS protecters in amongst the bits and pieces.

Very occasionally they'll come up on Ebay.

As you mentioned, I've never seen the result of a snapped chain with the protector fitted.

I think that it was a bit of a "Once bitten, Twice shy" situation where the guys who had busted out their cases previously learnt their lesson the expensive way and were a bit more mindful of the consequences from slack maintenance.

Mick

[MCRider]

Hi Ron

I've got 2 of these NOS protecters in amongst the bits and pieces.

Very occasionally they'll come up on Ebay.

As you mentioned, I've never seen the result of a snapped chain with the protector fitted.

I think that it was a bit of a "Once bitten, Twice shy" situation where the guys who had busted out their cases previously learnt their lesson the expensive way and were a bit more mindful of the consequences from slack maintenance.

Mick

Yup and that brings us to the mystery which may never be solved for sure, why were they breaking chains? Rocket3s/Tridents, hopped up Sportsters, H1s and H2s weren't breaking chains. Honda tried to sluff it off on maintenance but that wouldn't fly. Others say the materials weren't up to snuff, but I can't buy that, same stuff everyone else was using. It was such a random occurrence. Some bikes with perfect maintenance, snap. Others with pitiful maintenance...snap...or not.

For me the only thing that answers all the questions, the randomness, the "why me", etc. was the routing of the battery drain tube. It only takes a whiff of battery acid to damage a chain. But I could be full of it too.

I always thought the guards were neat in a sort of way. But now just one more thing to deal with which ultimately is not necessary.

[mystic_1]

The "case saver" will not save your case.

I'll post up pics tonight of the one I mangled a few years back.

mystic_1

[srook]

One thing that the CB750 has that old Triumphs do not is a wobbly front sprocket.  Not sure about the other Japanese superbikes of the day, but the Sportsters don't have it either.  I think this may have contributed to chain breakages as well.  As the sprocket wobbles, so does the chain, wearing into each other.  The rear sprocket is also rubber mounted and has the ability to wobble.  Just my thoughts.  Add battery acid and substandard chains to the mix = broken cases.
Scott

[donny]

 the olde timers around here go to the farm store to buy chain, cut to length.  They haven't heard of any failure. 
  I think with the humongous combines the soddies use nowdays, the chains are much stronger than implement chains circa 1969? ?  They do use many belts though.
Machinery has awesome torque on those chains when they put her in gear.
 

[mystic_1]

OK, here's the pics I mentioned.

My chain did not break.  In fact, although I believe I know when this happened, I wasn't fully aware of the extent of the damage until I parked the bike and saw the oil pouring out.  My best theory is that some debris of some sort was pulled through the chain run.  Not sure if it went between the chain and the sprocket or between the chain and the case saver.

As you can see the case saver, in fact, saved nothing.  The bolt holes simply tore out, and the entire case saver bent and was pushed into the crankcase, which collapsed inwards.

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mystic_1

[MCRider]

Yikes! You mean the crankcase bit it too, without the chain breaking?

If so that's a pretty good argument for not using it, seems?

[mick7504]

There's some damage there for sure.
I'm still curious to see the results of a full on hit from a broken chain. (With a protector installed)
The design would hopefully minimise the possibility of a broken chain slapping the top of the top case as well and busting out the primary sprocket cover.
Some motors I've seen have had the engine no casting become unreadable from a broken chain slap.
My thoughts have been that the bolts would be torn from the case which is preferable over an engine split.
Mick

[mystic_1]

Yikes! You mean the crankcase bit it too, without the chain breaking?

Yes, both the upper and lower cases suffered damage.  The lower casing was pushed inwards far enough that the inner surface contacted the transmission gears.  I should point out that my cases had been previously damaged in this area, and re-welded, by a PO.  The new damage didn't seem to follow the old welds, but I suppose it's possible that the previous welding had made the case brittle in that area.  Still, given the extent of the damage and the relatively mild nature of how it happened, plus how badly mangled the "case saver" was, I don't think it helped at all.

If so that's a pretty good argument for not using it, seems?

I've sometimes wondered, if the "case saver" were not there, would the debris or whatever simply passed through the chain run without causing this damage?  The world may never know, I suppose.

mystic_1

[Markcb750]

I see that device as protecting the case from a loose chain rubbing the case, more than protecting the case from a broken chain.  Not a lot of strength in that bracket to hold against a wadded up chain in the case.



**Maybe if it broke just right it would guid the broken chain out of the case, maybe.
 

[crazypj]

For me the only thing that answers all the questions, the randomness, the "why me", etc. was the routing of the battery drain tube. It only takes a whiff of battery acid to damage a chain. But I could be full of it too.

 Although they should have known better, in the mid 80's, Yamaha had a service bulletin (don't remember if it came to recall?) on RD350's because of chains breaking.
 It was a direct result of battery breather hose being too short and routed directly on top of chain. 
 The fix was re-routed longer breather

[Don R]

This was a blast from the past! I never did get one.

[MCRider]

For me the only thing that answers all the questions, the randomness, the "why me", etc. was the routing of the battery drain tube. It only takes a whiff of battery acid to damage a chain. But I could be full of it too.

 Although they should have known better, in the mid 80's, Yamaha had a service bulletin (don't remember if it came to recall?) on RD350's because of chains breaking.
 It was a direct result of battery breather hose being too short and routed directly on top of chain. 
 The fix was re-routed longer breather

Ta Da!  Thanks for that.

[mick7504]

Excellent info.