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Author Topic: Inline-four crankshaft  (Read 215191 times)

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Offline Interested Observer

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Re: Inline-four crankshaft
« Reply #255 on: November 10, 2015, 06:27:13 PM »
Various comments and questions--

1--  Ref. reply 253: “hardness is related to strength (both yield & ultimate), but it's more closely related to elastic modulus”.
Hardness is not related in any particular way to the elastic modulus.  The elastic modulus of steel is typically in a very narrow range for any grade or heat treatment.  Hardness can be all over the map.  The elastic modulus relates to elastic deformation, hardness relates to resistance to plastic deformation.

2--  I, too, am wondering about the aluminum(?) blocks.
3--  From the photos, I assume the right end of the rocker is “stationary” on the adjuster, the cam acts downward on the large roller in the middle, and the small roller actuates the valve stem.

If that is the case, it seems that this arrangement entails a larger amount of valve train inertia than most since the middle roller and the necessary reinforcement around it has to be accelerated in addition to the valve actuating end.  The polar moment about the fixed end is considerably larger than if the rocker rocked about the middle.  A problematic issue for a 10,000 rpm system.
4--  I assume the basic form of the rocker is a “U” shaped channel, with a continuous “floor” member from the pivot to near the small roller.  If that is the case, increasing the thickness of the floor through the middle section would be the most direct way of lowering the stresses in it. 
5--  The relatively long thin flanges of the U may present a buckling problem since they are in compression and are not particularly reinforced laterally.  This may visit grief on the roller retention mechanism.  May also introduce some weird harmonics to the valve train.  How “stiff” is this system?
6--  You definitely want the material to be “tough”.
7--  In your analysis, did you include the spring and valve masses?  What were the resulting max stresses, and where?  Was this an FEA analysis or by hand?
8--  Any successful 10,000 rpm valve train is usually a very highly engineered system. 

Offline wobblywalrus

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Re: Inline-four crankshaft
« Reply #256 on: November 10, 2015, 08:31:46 PM »
Jack, look at structural titanium when you do your calculations.  Like steel, it has a endurance limit for long term survival under cyclic loads.  It is also very strong so it is possible to overdesign your rocker arms, strengthwise, with minimal weight penalty.  Another good aspect is it provides good properties in its annealed state so you do not need to worry about heat treating and its side effects.

Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #257 on: November 11, 2015, 12:31:24 AM »
Each aluminum block has a pair of drilled passages to direct pressure oiling from the pivot ball to each end of the roller wheel axle. Metering of this oil is copied from rocker-pivot oiling scheme of the original '55 Pontiac V8 engine- a drilled passage through a cam journal, thus a "spurt" every revolution, plumbed to all eight pivot balls. The test spinning showed the oiling system functioning as planned.

Regarding acceleration forces in the valvetrain- yes, of course the mass of all moving parts was part of the calculations. The 10,000 RPM goal is not a "blue sky" number. It's based on years of experience with my pushrod hemi V8, with its massive (literally) valvetrain. It runs reliably to 9,000 RPM in competition. The four cylinder being developed uses one of the same hemi heads, same valve sizes, etc., but with much less reciprocating mass in its OHC valvetrain- so the 10,000 RPM capability is not at all an unreasonable expectation.

Again, thanks for the suggestions about redesign, alternative materials, etc. However, if it weren't for the one neglected stress riser in that one follower (oops!), I'd still be trying to make the valvetrain fail.

No FEA. Purely old-school approach. [Although a pocket scientific calculator beats the heck out of the old slide rule...]
M/T Pontiac hemi guru (or does guru status expire after 30 years?)

Offline Speed Limit 1000

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Re: Inline-four crankshaft
« Reply #258 on: November 11, 2015, 07:25:00 AM »
Quote from: Jack Gifford

No FEA. Purely old-school approach. [Although a pocket scientific calculator beats the heck out of the old slide rule...

The old slide rule got us to the moon and back each time. With all the computers in the world half of the mars missions have failed. Getting results to your problems faster may take less time but it doesn't always give better results. It is funny that now the lines on the old slide rule look smaller and harder to see :-o
John Gowetski, red hat @ 221.183 MPH MSA Lakester, Bockscar #1000 60 ci normally aspirated w/N20

Offline Freud

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Re: Inline-four crankshaft
« Reply #259 on: November 12, 2015, 02:30:48 PM »
Clean the slide rule in the dish washer. When it's clean

it's easier..............

Slide rules are SOP in Costa Rico.

FREUD
Since '63

Offline Speed Limit 1000

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Re: Inline-four crankshaft
« Reply #260 on: November 12, 2015, 05:46:01 PM »
Clean the slide rule in the dish washer. When it's clean

it's easier..............

Slide rules are SOP in Costa Rico.

FREUD

Freud, Good point. I will be back in Costa Rica on 24 November 8-)
John Gowetski, red hat @ 221.183 MPH MSA Lakester, Bockscar #1000 60 ci normally aspirated w/N20

Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #261 on: January 29, 2016, 01:45:37 AM »
Returning to my original purpose of this thread: attempting to educate myself somewhat about high-performance inline four cylinder engines.

Reading a 1953 Hot Rod Magazine article by Don Francisco about engine balancing, I was jolted by this statement: "If the crank is for an inline four cylinder or is a flat crank for a V8, proceed directly to balancing the crank- no need for bob weights."

Whoa! How did I make it to age 75 not knowing squat about engine balancing? All these years I blithely assumed that the bob weight formula (in a round-about way) provided an indication of the appropriate amount of mass for the counterweights of each rod throw.

So... what determines the ideal mass of a flat crank's counterweights? Or, in my case, when I asked Moldex to make me an 8-counterweight four-cylinder crank, how did they establish the size of the counterweights?

I've got an appointment with my "balance guy" tomorrow- hoping he can "enlighten" me.

[I realize that my use of the term "mass" above isn't totally correct- it's also necessary to know the radial distance of the center of that mass from the crank's center]
« Last Edit: January 29, 2016, 01:55:03 AM by Jack Gifford »
M/T Pontiac hemi guru (or does guru status expire after 30 years?)

Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #262 on: February 05, 2016, 01:21:00 AM »
While waiting for CNC replication of a set (& a spare set) of cam followers:

Made up the two required crank hubs (for cam-drive sprocket & for blower-drive pulley), so I could finish the final machining on the crank- fitting 1/4" round keys to drive the hubs- a "ticklish" job that I wasn't looking forward to. Had to offset the complete column/head of the mill 3" to the side (on 1" thick bars) to be able to hang the crank off the back of the table. Feed needed to be VERY slow (~.001"/sec) to avoid drills/reamer wander (2.700" deep)- but it came out well. Now it's off to the balance shop with the crank.
M/T Pontiac hemi guru (or does guru status expire after 30 years?)

Offline Rex Schimmer

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Re: Inline-four crankshaft
« Reply #263 on: February 07, 2016, 01:13:08 PM »
Nice job Jack! I have always liked "Dutch" pins and if you don't have keyway broaches it is a great way to key parts together. Doing it with a good drill and then a good reamer you get a really tight fit which can be more difficult with square keys. Max alias the "Kansas Bad Man" used Dutch pins on many of his Vincent parts for his MC streamliner.

Great job!
Rex
Rex

Not much matters and the rest doesn't matter at all.

Offline bearingburner

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Re: Inline-four crankshaft
« Reply #264 on: February 07, 2016, 04:09:59 PM »
My experience with a "Dutchman" is that you drill longitudinally down the joint between the two pieces and tap the resulting hole. Then thread in a set screw and lock with loctight.   



Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #265 on: February 09, 2016, 12:55:03 AM »
My sole reason for round-keying is reduction of stress-risers. Typically, driving a "lot" of blower from a Pontiac crank snout (only 1.375" diameter) is done with dual keys/keyways, which create so much stress that snout breakage is a concern. [In the lakester, there won't be enough room for a snout support in front of the blower pulley]
« Last Edit: February 09, 2016, 12:56:49 AM by Jack Gifford »
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Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #266 on: February 12, 2016, 12:47:24 AM »
Wow... I actually got something done FAST! Took the crank to the balance shop, expecting to pick it up sometime(?) later. I was surprised to hear "give me a hand and I'll do it now". Being a flat crank, there was no need for any Mallory metal and it really didn't require much correction. :-)
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Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #267 on: February 28, 2016, 01:43:00 AM »
CNC'd followers should be done this week.

Plugging away at other stuff- machining of blower manifold pieces mostly done. Won't finish the top plate (1/2" 6061) until the blower is in-hand, and haven't decided whether to build a pop-off valve or simply buy a burst panel.
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Offline Jack Gifford

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Re: Inline-four crankshaft
« Reply #268 on: March 08, 2016, 01:19:24 AM »
Received the CNC-milled revised design cam followers (plus 8 spares) a couple of days ago. They look good, except for a miscommunication regarding clearance to the spring retainers. The shop took the liberty of creating an almost-square-cornered "step" (only .030" radius insude corner), so I milled them to a smooth radius at that area. They also didn't check with me before changing my .096" oil feed passage to .125" (to utilize a thread former, rather than a tap). This messed up my re-use of the aluminum oil-manifold pieces, so I had to rework those. Some more minor detailing and they'll be ready for heat-treat and assembly.

[My new byline: "Hey, it's only money..."]
« Last Edit: March 08, 2016, 01:27:11 AM by Jack Gifford »
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Offline fordboy628

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Re: Inline-four crankshaft
« Reply #269 on: March 08, 2016, 04:13:04 AM »
Very nice Jack.

If the CNC shop did not follow the print and made changes without consulting you, I'd have them make another set, on their dime.   That's why prints exist, so the designer's decisions on part dimensions and form can be communicated to manufacturers/fabricators without errors or changes.   If you are trying to maintain a some sort of relationship with the shop, I understand why you might be reluctant to push the issue though.   Finding capable suppliers for small quantity prototype parts is always difficult, it gives me a headache just thinking about it . . . . .   :cry:

Hope everything works the way you have planned.   It's looking like things are coming together for you.

 :cheers:
Fordboy
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