ADVrider

Go Back   ADVrider > Bikes > Old's Cool > Airheads
User Name
Password
Register Inmates Photos Site Rules Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Search this Thread Display Modes
Old 03-09-2013, 05:36 PM   #166
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,275
Quote:
Originally Posted by adrenal View Post
I don't profess to be an expert in pushrods by any stretch. There are no doubt lots of considerations identified by people who make pushrods their living about which I haven't a clue.

Strength of materials is part of my living and in this area the numbers speak for themselves. What's important in all of these technical discussions, is to clearly define your objectives. If you don't, then things can go round and round n rou... as is so often the case in so many threads. If you are talking stock or mildly hopped airheads then what Manton advised could be true.

However, the following statements from Dirk had me springing from my lurking cupboard: ' Now we can rev up to 10.000 rpm and the engines feel like overhead cammed - never crashing any valve at lifts you would not believe.' And: 'They are able to transport the cam information 1:1 from the cam to the valve...and this is more then essential and makes it perform like an overhead cam engine. Very silent, very smooth and very strong.'

To the computer! Took a punt on forces and did some FE modelling in the contex of high performance airheads aiming to minimise flex. The absolute numbers are less important than the relative results between materials and cross-sectional area. Not sure if 14mm at midpoint of rod will interfer with the tube but wouldn't be far off I reckon.

Anyway, for me it was an interesting exercise which corroborated what Dirk was saying.

BTW: Thanks Dirk, your contribution here has been fascinating.
Yep, britten and Tesla rock!
Numbers speak for themselves? Sure. If you don't care how they were derived. It just happens that how you get the numbers is more important than the numbers.

My research didn't involve stock or mildly modified engines at all. Most of my research centered around NASCAR and NHRA top fuel and branched out from there. Tapered aluminum rods might be enough for our engines. The people I talked to in the business said that for the spring pressures most of their clients ran (not close to stock mind you), aluminum was completely out of the picture not rigid enough. After telling two different companies of my situation and the comparatively puny spring pressure that I run, they both still recommended 4130 rods. I was still undecided until I found a bunch of BMW steel rods (probably 1018) which are much heavier than their aluminum rods and they still showed signs of flexing like their aluminum rods. They don't show signs of flexing nearly as much as their aluminum rods but . . . . That's when I figured the experts I talked to were probably right.

supershaft screwed with this post 03-09-2013 at 05:53 PM
supershaft is offline   Reply With Quote
Old 03-09-2013, 06:50 PM   #167
adrenal
www.cafebeemer.com.au
 
adrenal's Avatar
 
Joined: Jun 2008
Location: Melbourne, Australia
Oddometer: 463
Fair enough SS. But I sense yet another context error: steel best for Nascar and tapered AL alloy good for hopped airheads perhaps? I can't say for sure because I'm not an 'expert' on the subject of pushrods. i.e. someone with the 1st hand experience of endless detailed experimentation.

I commented - with caveats - on an area in which I have 1st hand experience. That's all.

P.S. Even experts disagree with oneanother.

Health warning. This post may contain traces of nut.
__________________
Adrian
cafebeemer is now:http://www.skrunkwerks.com
farcebook page: http://facebook.com/skrunkwerks
instagram: #skrunkwerks

adrenal screwed with this post 03-10-2013 at 03:47 PM
adrenal is offline   Reply With Quote
Old 03-09-2013, 07:05 PM   #168
RecycledRS
Along for the ride
 
RecycledRS's Avatar
 
Joined: Nov 2008
Location: Vancouver Island
Oddometer: 1,036
SS, what do you set the cold gap at for 4130 push rods? Given the different expansion rates
of aluminium barrels and steel push rods I wonder if this will be an issue.
__________________
_____________________________________
"There's a fine line between a shearing and a skinning"

RecycledRS screwed with this post 03-09-2013 at 07:14 PM
RecycledRS is online now   Reply With Quote
Old 03-09-2013, 07:11 PM   #169
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,275
Quote:
Originally Posted by adrenal View Post
Fair enough SS. But I sense yet another context error: steel best for Nascar and tapered AL alloy good for hopped airheads perhaps? I can't say for sure because I'm not an 'expert' on the subject of pushrods. i.e. someone with the 1st hand experience of endless detailed experimentation.

I commented - with caveats - on an area in which I have 1st hand experience. That's all.

P.S. Even experts disagree with oneanother.

Health warning. This post may contain traces of nut.
That very well could be. Doubtful according to who I talked to but . . . .
supershaft is offline   Reply With Quote
Old 03-09-2013, 07:13 PM   #170
supershaft
because I can
 
Joined: Sep 2010
Location: San Francisco Bay area
Oddometer: 8,275
Quote:
Originally Posted by RecycledRS View Post
SS, what do set the cold gap at for 4130 push rods? Given the different expansion rates
of aluminium barrels and steel push rods I wonder if this will be an issue.
Zero lash on the exhaust and one hour off the clock tight on the intakes is getting me to around where I want hot.
supershaft is offline   Reply With Quote
Old 03-09-2013, 07:37 PM   #171
adrenal
www.cafebeemer.com.au
 
adrenal's Avatar
 
Joined: Jun 2008
Location: Melbourne, Australia
Oddometer: 463
Quote:
Originally Posted by US_Marshall View Post
Your models show solid push rods. What affect is there when they are hallow? The increased surface area should increase rigidity of the unit.
This one is interesting as it pops up regularly and i wonder why it seems intuitively correct.

It might be this: For two round shafts of equal weight, one solid, one hollow, the hollow one, by definition must have a larger outer diameter and will be stiffer because of reasons outlined in above posts. (as long as wall thickness is not too thin). So it's a matter of stiffness V's weight efficiencies. It is for this reason that the world is full of round hollow objects, which might give rise to the misnomer that the internal surface area somehow adds to stiffness.

It still surprises me how far this can be pushed - e.g. how light those heavy looking car tail shafts actually are. If you were to collapse that same amount of material into a solid shaft, it would snap just as you lifted the clutch. We're talking of torsional stiffness here but similar rules apply.

On the flip side, the fact is, for two shafts of equal outer diameter a solid one will always be stiffer than its hollow partner.

However! The influence of material on stiffness diminshes at an exponential rate the closer that material is to the center line. So, you can remove a a goodly amount from the center without reducing the stiffness too much.


Health warning: this post definitely contains traces of nut
__________________
Adrian
cafebeemer is now:http://www.skrunkwerks.com
farcebook page: http://facebook.com/skrunkwerks
instagram: #skrunkwerks

adrenal screwed with this post 03-10-2013 at 02:46 PM
adrenal is offline   Reply With Quote
Old 03-09-2013, 08:29 PM   #172
Plaka
Brevis illi vita est
 
Joined: Jun 2010
Oddometer: 4,581
Quote:
Originally Posted by adrenal View Post
I don't profess to be an expert in pushrods by any stretch. There are no doubt lots of considerations identified by people who make pushrods their living about which I haven't a clue.

Strength of materials is part of my living and in this area the numbers speak for themselves. What's important in all of these technical discussions, is to clearly define your objectives. If you don't, then things can go round and round n rou... as is so often the case in so many threads. If you are talking stock or mildly hopped airheads then what Manton advised could be true.

However, the following statements from Dirk had me springing from my lurking cupboard: ' Now we can rev up to 10.000 rpm and the engines feel like overhead cammed - never crashing any valve at lifts you would not believe.' And: 'They are able to transport the cam information 1:1 from the cam to the valve...and this is more then essential and makes it perform like an overhead cam engine. Very silent, very smooth and very strong.'

To the computer! Took a punt on forces and did some FE modelling in the contex of high performance airheads aiming to minimise flex. The absolute numbers are less important than the relative results between materials and cross-sectional area. Not sure if 14mm at midpoint of rod will interfer with the tube but wouldn't be far off I reckon.

Anyway, for me it was an interesting exercise that corroborated what Dirk was saying.

BTW: Thanks Dirk, your contribution here has been fascinating.
Doch, Britten und Tesla rock!
Did that modeling consider resonance? I bet there are some engine speeds where the pushrods are trying to crash into themselves. So controlling the harmonics (which you might do with geometry) matters.
Plaka is offline   Reply With Quote
Old 03-09-2013, 08:37 PM   #173
Houseoffubar
fine beer sampler
 
Houseoffubar's Avatar
 
Joined: Dec 2010
Location: Bothell, Washington
Oddometer: 1,758
I have learned more about push rods here, than any of the other exhaust threads!
__________________
1978 R100/7 Build thread 1915 Boardtrack racer replica (Electric Powered) Lots of bicycles
Hemp: The strongest natural fiber in the world, and the most nutritious plant on earth.....why is this illegal again?
Houseoffubar is offline   Reply With Quote
Old 03-09-2013, 08:48 PM   #174
Plaka
Brevis illi vita est
 
Joined: Jun 2010
Oddometer: 4,581
Quote:
Originally Posted by adrenal View Post
This one is interesting as it pops up regularly and i wonder why it seems intuitively correct.

It might be this: For two round shafts of equal weight, one solid, one hollow, the hollow one, by definition must have a larger outer diameter and will be stiffer because of reasons outlined in above posts. (as long as wall thickness is not too thin). So it's a matter of stiffness V's weight efficiencies. It is for this reason that the world is full of round hollow objects, which might give rise to the misnomer that the internal surface area somehow adds to stiffness.

It still surprises me how far this can be pushed - e.g. how light those heavy looking car tail shafts actually are. If you were to collapse that same amount of material into a solid shaft, it would snap just as you lifted the clutch. We're talking of torsional stiffness here but similar rules apply.

On the flip side, the fact is, for two shafts of equal outer diameter a solid one will always be stiffer than its hollow partner.

However! The influence of material on stiffness diminshes at an exponential rate the closer that material is to the center line. So, you can remove a a goodly amount from the center without reducing the stiffness too much.

But there are limits of course. i could go on...

Health warning: this post definitely contains traces of nut
Are you talking about stiffness as resistance to bending? A tube is subject to buckling. (The accordian effect). The walls of the tube act as beams in and of themselves. So the thicker they are the greater the beam strength. At the limit you get a solid shaft. At the same limit the distance to the furthest fiber is zero so the material in the center is not consequential to bending. it means a lot to buckling however.
Plaka is offline   Reply With Quote
Old 03-09-2013, 11:18 PM   #175
adrenal
www.cafebeemer.com.au
 
adrenal's Avatar
 
Joined: Jun 2008
Location: Melbourne, Australia
Oddometer: 463
Plaka,
I didn't want to overcomplicate things so limited the conversation to stiffness in relation to bending and only hinted at thin wall effects. You are right: A rod can only be hollowed out so much before the failure mode swiches to thin wall local buckling and you start going backwards.

Re modal analysis, my FE program is not sophisticated enough to analyse it fully and nor am I!. There is no doubt that all sorts of crazy harmonics would be going on at high engine speeds with the rods whipping around all over the shop. Extremely difficult to model. Thats when you get out a strobe and use your eyeballs!

Interesting thing: The 1st order static analysis told me that deflection as a result of bending due to an offset load is bugger all! Not enough to account for interference with the pushrod tube in my view.

But bending + high frequency modal effects certainly could produce big deflections and is the most probable cause of the scuffed ring that we see on our pushrods and surely effects the transmission of information from the cam through to the valve.

The difference in modal properties between steel and aluminium is huge. Another factor in the choice of either AL or FE for a particular engine.

I have a feeling that someone in this thread, who shall remain nameless, Dirk, may have witnessed the above and chose a material accordingly.
__________________
Adrian
cafebeemer is now:http://www.skrunkwerks.com
farcebook page: http://facebook.com/skrunkwerks
instagram: #skrunkwerks

adrenal screwed with this post 03-09-2013 at 11:55 PM
adrenal is offline   Reply With Quote
Old 03-09-2013, 11:22 PM   #176
adrenal
www.cafebeemer.com.au
 
adrenal's Avatar
 
Joined: Jun 2008
Location: Melbourne, Australia
Oddometer: 463
Quote:
Originally Posted by Houseoffubar View Post
I have learned more about push rods here, than any of the other exhaust threads!
Great isn't it! Thats why I don't mind thread drift. I've found so many gems hidden in threads that have nothing to do with the original topic.
Apologies to the OP
__________________
Adrian
cafebeemer is now:http://www.skrunkwerks.com
farcebook page: http://facebook.com/skrunkwerks
instagram: #skrunkwerks

adrenal screwed with this post 03-09-2013 at 11:30 PM
adrenal is offline   Reply With Quote
Old 04-25-2013, 08:53 PM   #177
darklight79
scaffold builder
 
Joined: Jun 2010
Location: Eureka ,Calif
Oddometer: 419
Y pipe

So backwards logic here ...So if 2 to 1 exhaust is ok and it is Can the dumping of the collector box be approved ,? The y pipe is all shiny sitting on the bench top Logic sez do it but there seems to be some discussion about removing the collector on a gs
darklight79 is offline   Reply With Quote
Old 04-26-2013, 01:47 PM   #178
Biebs
BMW Airhead
 
Biebs's Avatar
 
Joined: Mar 2012
Location: Cave Creek AZ
Oddometer: 447
Wicked 89 GS R100 stock exhaust

Previous owner tod me this was the only motorcycle he ever had with a catilytic converter - reffering to the collector box.


1. it weighs more than a Y - pipe.

2. Y - pipe is an after market add on so is a great selling point to someone??

3. y - pipe looks cool and after you install it you can point it out to your friends.

4. Y - pipe is a solution looking for a problem.


OK point is Stock collector box works but seeing you have the Y- pipe on your bench either install it or Ebay it!!!


But do save the original collector box for the next owner.
Biebs is offline   Reply With Quote
Old 04-26-2013, 03:01 PM   #179
Airhead Wrangler
Adios Mexico
 
Airhead Wrangler's Avatar
 
Joined: Mar 2008
Location: Back in Seattle, FINALLY
Oddometer: 6,344
The stock collector weighs a LOT. Ditching it in favor of a y-pipe will net you about 5-6 pounds
__________________
R80ST Gets The HPN Treatment
Seattle to TDF on an airhead

Current rides: HPN #834, '93 R100GSPD "red rocket", '73 R75/5 Toaster mongrel, '80 Ducati Pantah 500SL, '92 DR350, '67 Honda SS50, '80 Honda Chaly.
Airhead Wrangler is online now   Reply With Quote
Old 04-27-2013, 01:48 PM   #180
darklight79
scaffold builder
 
Joined: Jun 2010
Location: Eureka ,Calif
Oddometer: 419
found updated info on boxer parts to answer my questionhttp://www.boxxerparts.de/product_in...-with-ABE.html
darklight79 is offline   Reply With Quote
Reply

Share

Thread Tools Search this Thread
Search this Thread:

.
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


Times are GMT -7.   It's 04:29 PM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014