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Author Topic: Motorcycle crankcase expert needed  (Read 3042 times)
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wobblywalrus
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« on: January 15, 2018, 10:41:35 PM »

These case halves are held together by bolts.  It takes far less torque to remove them than to install them.  Shiny areas on the mating surfaces indicate the halves may be rubbing against each other.

What I want to do is send these halves to the one of the best experts we have in this country to get an opinion about what to do.  Any recommendations on who this might be?


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John Burk
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« Reply #1 on: January 16, 2018, 12:24:45 AM »

Up the bolt/stud size for more clamping pressure .

Tom Evans , motorcycle inspector would know .
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Buamotorsport
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« Reply #2 on: January 16, 2018, 12:39:09 AM »

Can I suggest Larry McBride the drag racer. I have his contact detail if you want them.

But first look....what are they from? If itís Honda, Kawasaki, etc then you could try to increase the bolt size but, be very careful as there doesnít seem to be much metal around the stud/bolt holes.

Talk to Larry he builds his own motors and can hopefully give you guidance.
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maj
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« Reply #3 on: January 16, 2018, 06:29:25 AM »

Bo on the Suzukis we use studs with higher torque values , but the catch is stud diameter can interfere with the case alignment  (oversize the non threaded half )
and extra tension can change the shape of the bearing bore (rehone)
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ggl205
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« Reply #4 on: January 16, 2018, 08:37:37 AM »

I am no MC engine expert but main saddle bolt holes appear to be sleeved. Those should keep main bearings located even if case halves squirm a bit. If you want to keep both case halves from moving but don't change bolt diameters, I would try putting a few more locating/retaining dowels around the case where there is sufficient material to do so.

John
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TheBaron
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« Reply #5 on: January 16, 2018, 12:03:33 PM »

A few things to consider:

Are all the "Dowels" snug in their bores and inplace?

Are there "Hard" washers under the Nuts and Bolt heads And are you lubing them? If the fasteners turn against the  aluminum you will have issues.

Are you retorquing the case fasteners after  a few heat cycles on the engine.

Short fasteners  do not hold their settings as well as long studs and bolts and often need retorquing (fasteners are springs in tension after all).

Robert in Costa Mesa
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wfojohn
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« Reply #6 on: January 16, 2018, 12:35:19 PM »

Helicoil the bolt holes so you are pulling steel to steel instead of steel to aluminium and retorque after each of the first 2 heat cycles.
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edinlr
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« Reply #7 on: January 16, 2018, 02:32:33 PM »

When I talked to ARP about making studs for my CX Hondas, they said first that they did not have any that would fit.  When I inquired about having them made, their response was that there was not enough depth for the studs to grab to do their job.  New bolts were not offered up based on the same theory.  At this point a perfect Helicoil seems the only option when there are issues. 

Are you having problems with the cases, or just concerned about the contact?  Most, if not all of the big four cylinder Jap bikes split their cases this way and this isn't usually a problem area.  If you did any machining to match the cases then you to line bore the cases and probably have other issues develop too.  Unless you are having a problem I'm not sure I would worry about it to much.
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wobblywalrus
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« Reply #8 on: January 17, 2018, 12:41:47 AM »

The bolts were tightened to 10 Nm and then 75 degrees of turn was added.  These are 1.5 mm pitch threads.  75/360 X 1.5 = 0.31 mm  The added turn gave 0.31mm more stretch.  Removing the bolts took about 10 Nm.  It appears the 0.31 stretch disappeared.  Either the bolts stretched or the crankcase deformed.

This is what I know about the cases.  They were made by SKF, they are die cast, and they are "LM2 to JVM Specifications."  The typical alloy for this die casting is A380 with a 23 ksi yield strength.  The area under the bolt head is 0.299 inches.  Yield occurs in the aluminum under the bolt head at:

23 ksi x 0.299 sqin = 6.88 kips tension to cause yield in the aluminum under the bolt head.  Tomorrow I will look at the tension to cause thread pullout.
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salt27
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« Reply #9 on: January 17, 2018, 01:44:02 AM »

Bo, I assume that there is some sort of gasket involved?

  Don
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TheBaron
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« Reply #10 on: January 17, 2018, 09:55:38 AM »

"Good Grief Charlie Brown!"    you are trying to stretch a case fastener .012" of an inch (.31mm)

Does not this sound like a bit much ?

Moving the decimal point one place to .0012"  seems more in line to me....

TRD had us using the "Torque then Turn (so many degrees)" method when assembling the all alloy Champ Car V-8 motors back in 1997 when I was there. There was no gasket, only sealer on the castings.

I hated doing it as it just crushed and deformed things all over the place. Aluminum is so soft and uneven in hardness that you are almost guaranteed to crush into it with this method....
 
I overhauled many Continental and Lycoming 4 and 6 cylinder aircraft engines and a few Pratt and Whitney radial engines back in the 70's. They all used the same method on the crankcase thru-studs,,,, Lube the threads as directed, torque them down in the order specified to the value specified, and use a freshly calibrated torque wrench! No Issues ever .

my 2 cents........

Smitty

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wobblywalrus
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« Reply #11 on: January 17, 2018, 10:34:25 AM »

That is why I posted it.  These might be "torque to yield" fasteners where the bolt is under plastic deformation.  The cases and where the head of the bolt seats do not appear to be distorted.  Some late night calcs showed that a bolt with less than 71ksi steel would stretch before it distorted the seat.  There is no gasket.   
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TheBaron
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« Reply #12 on: January 17, 2018, 12:22:04 PM »

If they are "torque to yield"  fasteners then one-time use would be mandatory,,,, is that spelled out anywhere in your service specs?



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Interested Observer
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« Reply #13 on: January 17, 2018, 02:20:39 PM »

Scaling the geometry of the bolts from the photo in reply #3004 of the Go Dog thread, and unlimbering the electronic sliderule, we find that the 40 Nm makeup would produce 5,841 lb force per bolt assuming a friction coefficient of 0.12 in the (loctited) threads and 0.08 at the underhead surface.  This makes a longitudinal stress of 51,500 psi in the large diameter shank and 73,540 psi in the smaller shank.  The breakout/make-up ratio is 0.289, so since the 40Nm makeup is about 30 lb-ft, the reported 10 lb-ft breakout is to be expected.

For the second make-up method, 10 Nm followed by 75 degrees of rotation, we get a total of 13,523 lb force per bolt and stresses of 119,235 and 170261 psi ASSUMING WE ARE STILL IN THE ELASTIC RANGE OF THE BOLT MATERIAL.  Which we probably are not.  If not, these numbers would be lower, to be determined by the stress-strain curve of the material.  The breakout/make-up ratio remains the same but would depend on the actual final achieved preload.

Take a bolt to the local Instron machine and find out what it does.
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wobblywalrus
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« Reply #14 on: January 18, 2018, 08:29:56 PM »

Triumph does not advise against bolt reuse.  Tonight the main bearing clearances will be checked and I will check a few bolts for permanent deformation.  They need to be installed and removed to check the clearances.

The ARP catalog, pages 21 and 22 give instructions for ordering custom studs or bolts.  Triumph does advise against using more torque or turn than specified.  They say the engine will be tight and have premature wear.  A phrase I am considering for the work order is "The new bolts should provide installed clamping force similar to the bolts used now.  The objective is for them to maintain this clamping force after use."   
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