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Author Topic: Motorcycle crankcase expert needed  (Read 3951 times)

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Offline WhizzbangK.C.

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Re: Motorcycle crankcase expert needed
« Reply #15 on: January 18, 2018, 07:45:29 PM »
Just a thought that entered my mind, probably not directly applicable to this situation but somewhat related. The cylinder studs on Volkswagen air cooled engines used a thick washer under the nut against the cylinder head. I have no idea what this washer was made of, but from experience I found out that substituting a steel one in its place would result in pulled threads in the case, especially on big bore high compression builds. I never had an issue as long as the correct washers were used, but pulled several when wrong ones were installed. My working theory at the time was that the washers were a special alloy that worked as a kind of spring to compensate for cylinder growth under operating heat and maintain more or less consistent tension on the studs.
Ah, this is obviously some strange usage of the word 'safe' that I wasn't previously aware of.  Douglas Adams

Offline Interested Observer

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Re: Motorcycle crankcase expert needed
« Reply #16 on: January 19, 2018, 08:07:22 AM »
Quote
The objective is for them to maintain this clamping force after use.

Wobbly, what makes you think the bolts “lose” their preload capacity just because they have been slightly stretched?  Just because they may have been somewhat “yielded” doesn’t mean they have lost strength or load capacity.  They may have gotten longer but are still carrying the load that caused them to get longer.

The “yield point” of ductile materials is generally obtained during tensile testing at a point of 0.2% of plastic offset--that is, the material has already undergone some “set” just to obtain that basic information.  When the test is continued, the specimen will continue to carry more and more load at much greater amounts of strain, and the ultimate strength is always greater than the “yield” strength.

The 0.31 mm elongation added to the bolt by the 75 degree turn amounts to only 0.4% strain--just barely(0.2%) past the minimal amount used to determine the yield point.

Consider:
1)  That’s what Triumph says to do.
2)  When you do that, with the bolt loaded up to that degree, both they and you are satisfied.  The bolt is supporting the desired load in a slightly yielded form.
3)  Removing the bolt won’t alter its form.
4)  Reinstalling the bolt returns it to the same load condition that it was satisfactorily sustaining previously--so what’s the problem?

Based on the two make-up methods it seems that Triumph are shooting for about 6000 lb preload for the bolts and are using something like 75 ksi yield material to limit it to that neighborhood but insure that it is at least there with the 75 degree turn method.

Offline manta22

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Re: Motorcycle crankcase expert needed
« Reply #17 on: January 19, 2018, 09:10:42 AM »
Whizzbang;

Could those special washers be Belleville washers?

Regards, Neil  Tucson, AZ
Regards, Neil  Tucson, AZ

Offline WhizzbangK.C.

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Re: Motorcycle crankcase expert needed
« Reply #18 on: January 19, 2018, 06:59:12 PM »
Whizzbang;

Could those special washers be Belleville washers?

Regards, Neil  Tucson, AZ

No, not Belleville type, no cup to them at all. Visually they appeared to be just a thick flat washer, but as I recall they weren't steel. More like a brass or bronze type alloy IIRC. It's been over 30 years so my memory may be just a bit vague.  :cheers:
Ah, this is obviously some strange usage of the word 'safe' that I wasn't previously aware of.  Douglas Adams

Offline wobblywalrus

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Re: Motorcycle crankcase expert needed
« Reply #19 on: January 19, 2018, 08:14:36 PM »
The bolts are losing clamping force.  Case separation results in lubrication failure to critical parts with drastic and sudden bad results at the worst possible time.  This problem is not uncommon to hopped up jap bikes.  The big plan continually changes while I learn more and get advice.

The current plan is to torque down the standard Triumph bolts as recommended by them and to measure the ID of the crank journal shell housings without the shells.  Studs or bolts made by ARP to their recommendations will be installed to their torque values.  Then I will check the housing diameters and contact them for advice if there are any problems.

The ARP folks deal with this stuff on a daily basis.  I do not have a clue.  This seems like a good approach to the issue.

Offline wobblywalrus

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Re: Motorcycle crankcase expert needed
« Reply #20 on: January 20, 2018, 02:36:51 PM »
A call was made to the fellow who runs and develops the bikes for the Triumph race team.  The manual says to initially tighten all bottom case bolts to 10Nm then flip the engine over and tighten the top bolts to 10Nm before proceeding to the final tighter torque values.

The additional step he recommends to to repeat this first step at 10Nm until there is no movement in any bolts before proceeding to the higher torque values.  He said this should fix my problem.  I did this and it does result in more degrees of turn on those big retaining bolts to get to 10Nm before the final 75 degrees of turn.

Uncoated rod bearing shells should work just fine, he says, and they run there engines up to 10,000 rpm.  My rod bearing problem might be caused by oil pressure loss when the cases separate and it might disappear when the cases are torqued down tighter.  Uncoated rod bearings will be tried this year along with standard Triumph case bolts.       

Offline edinlr

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Re: Motorcycle crankcase expert needed
« Reply #21 on: January 29, 2018, 10:43:14 AM »
http://www.cyclexchange.net/Machine%20Work%20&%20Services.htm

Here's a link for Cycle Exchange.  They mainly work on old Honda 4s.  They have some discussion down to the middle of the page about crankcase alignment and even determining when you have torques the case too tight and are binding the crank.  They do some work to correct this.
Honda CX650 turbo

Offline Vinsky

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Re: Motorcycle crankcase expert needed
« Reply #22 on: January 29, 2018, 12:45:00 PM »
ARP has a recommended torque chart and also an assembly lube recommended on the bolts for the correct torque values.
http://img.photobucket.com/albums/1003/SCHWARZERM/Car%20Technical/ARP_TORQUE.jpg?hotlinkfix=1517251304858
John

Offline CNC-Dude

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Re: Motorcycle crankcase expert needed
« Reply #23 on: February 02, 2018, 03:53:58 PM »
The bolts are losing clamping force.  Case separation results in lubrication failure to critical parts with drastic and sudden bad results at the worst possible time.  This problem is not uncommon to hopped up jap bikes.  The big plan continually changes while I learn more and get advice.

The current plan is to torque down the standard Triumph bolts as recommended by them and to measure the ID of the crank journal shell housings without the shells.  Studs or bolts made by ARP to their recommendations will be installed to their torque values.  Then I will check the housing diameters and contact them for advice if there are any problems.

The ARP folks deal with this stuff on a daily basis.  I do not have a clue.  This seems like a good approach to the issue.

It more than likely will make the housing bores smaller when switching to ARP fasteners because of their higher torque requirements. This is also common in automotive engines when switching from OEM bolts to ARP studs as well. You will often need to hone the housing bores larger to get them back in spec. But also will allow you to go slightly to the high side of the specs to get you the extra few tenths of clearance you were needing.

Offline wobblywalrus

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Re: Motorcycle crankcase expert needed
« Reply #24 on: February 02, 2018, 10:09:19 PM »
Triumph made two crankcase bolt modifications.  I did the first modification a few years ago.  This year the second one will be tried with the bolt torque procedure I learned from the Triumph flat track bike tuner.  New bolts of the latest style will be used.  This concept works OK on the flat track bikes and they rev to over 10,000 rpm.  Mine rev limiter is at 9,000 so their method is likely to fix the problem.

The crank shells I bought were early model ones.  The shell part number changed but the dimensions appear to be identical.  The numbers stamped on old and new style shells are different.  The shell manufacturer website says the new model shells have a more durable surfacing based on those stamped numbers.  New model shells are on order and should arrive in mid February.  Thriumph parts are expensive and they take a long time to get.

Crank bearing clearances in the past were set to values recommended by Mr Mc Knight of Mahle which are 0.00075 to 0.001 inches per inch crank diameter with an extra 0.0005 clearance for racing.  This is 0.0016 to 0.0020 for the crank.  Triumph recommends 0.0007 to 0.0017  Mine are at 0.0015  This is OK by my thinking.  The clearance will increase when the aluminum crankcases warm up and it should be right in the middle of Mahle's clearance range at operating temperature.

Crank shells are the largest I can get and there is not enough clearance between them and the crank for polymer coating.   New cases cost $3900 on Bike Bandit so I hesitate to do any modifications to the ones I have unless I run out of alternatives.

The rod big end shells are Triumph ones.  They are used on hopped-up rocket 3's with 80 HP per cylinder and 767 cc cylinders.  My engine has 500 cc cylinders with 53.5 HP per cyl.  The big end shells should be good enough.  Mahle's recommended clearance is 0.0017 to 0.0021.  Mine are at 0.002 so they should be OK.  These are steel rods on a steel crank so clearances are not expected to increase much when the engine warms up.

An article on engine building I am reading says that good crush is needed to get adequate heat transfer from the shell to the rod and from the shell to the crankcase.  Honing the rods or cases might be problematic if too much crush is lost and heat transfer becomes an issue.  Uncoated shells in standard size bores will be used for now.  I lack the tools and skill to evaluate and measure both bores and crush.

This engine building is sorta mental.  It does not come naturally to WW.