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Author Topic: Re-centering crank?  (Read 1804 times)

AgentX

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Re-centering crank?
« on: July 07, 2012, 07:33:25 AM »
Hi guys- Mr. Hopeless here again.

Working with a friend who has rebuilt a number of Enfields, I re-assembled my 1977 350cc engine with new barrel, piston, and rings.

He claims he noticed the piston "is a little to the left" in the new bore, and says I need to take off the timing cover and use a chisel to force the crank 1-2mm to the right.  Otherwise, he says, the engine will seize.

I am dubious of this claim and methods, but have no experience to make a call.  Can't find any mention in Snidal's or other manuals and online resources of this type of operation.  Can/should the crank even move laterally in the cases?

There is currently no play in any direction at the crank, as felt from the primary side.  We didn't touch anything at the conrod when we did the swap; just pinned in the new piston and rings, then lowered the barrel over it.  Conrod showed zero up/down play and the permissible slight side-side movement.

It is, however, very possible that the new bore is not perfectly manufactured and the center is not the same as on the old one, so maybe he's got a point, even if the suggested remedy is not correct.  Or else he's completely right and I'm just too arrogant and doubtful...been burned a few times already by Indian shade-tree mechanical lore, which is too often taken as gospel.

What do you gurus think I should do?  Further tests and/or final actions?  Appreciate the advice.

MD


Edit:  Mr. Snidal seems to agree with me, but does say that pulling the crank from the timing side can be acceptable.  Hmm...still ambivalent.

Quote from: P.S.
Excessive Force

Bear in mind at all times that force applied to either crankpin will be transmitted as a bending moment to the assembly of the flywheels and journal pin, thus tending to destroy crankshaft alignment. Thus, no force should be applied to the timing-side crankpin to force the drive-side pin into the bearings, for example. Nor should force be applied in the second stage to the timing-side case to force it over the timing-side bearing. In either case (no pun intended!), force should be applied only to the flywheel of the side concerned. Or as a pulling force from the outside of the case, pulling the shaft through the bearing.

Edit II:  In rotating the crank with a wrench, I am feeling a noticeable change in resistance as I turn.  So maybe something really is out of alignment?
« Last Edit: July 07, 2012, 10:20:09 AM by AgentX »

ace.cafe

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Re: Re-centering crank?
« Reply #1 on: July 07, 2012, 03:06:03 PM »
Sounds like you have a problem with your crank.
The con rod should be centered on the case split when you lean the con rod against the case.''

Also, there should be no binding of any sort when rotating the crank by hand with the barrel and head off. It should be as smooth as silk.

I think you need to dismantle the bottom end and re-do it properly.
DO NOT bang on that thing with a chisel, PLEASE.
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AgentX

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Re: Re-centering crank?
« Reply #2 on: July 07, 2012, 04:12:17 PM »
Sounds like you have a problem with your crank.
The con rod should be centered on the case split when you lean the con rod against the case.''

Also, there should be no binding of any sort when rotating the crank by hand with the barrel and head off. It should be as smooth as silk.

I think you need to dismantle the bottom end and re-do it properly.
DO NOT bang on that thing with a chisel, PLEASE.

Thanks for the advice.  My hopes for mobility in the near future are getting dimmer and dimmer...

Believe me, mention of a chisel was why I posted here in the first place.


Ed:  I may just try and swap back the old piston and iron barrel to see if they're turning smoothly or have the same change in resistance.  Not unthinkable that the alloy cylinder is badly/differently machined, and the iron had been working just fine before.

Kevin Mahoney

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Re: Re-centering crank?
« Reply #3 on: July 08, 2012, 04:29:59 AM »
I am not following your mechanics reasoning at all. Can  you ask him to be more clear. When the piston is in the barrel you can't tell left right or center. It sounds like a bit of shade tree vodoo to me.

AgentX

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Re: Re-centering crank?
« Reply #4 on: July 08, 2012, 08:46:56 AM »
I am not following your mechanics reasoning at all. Can  you ask him to be more clear. When the piston is in the barrel you can't tell left right or center. It sounds like a bit of shade tree vodoo to me.

"It is to the left."

Clarity, completeness, or correlation with reality based on observable, repeatable testing are not hallmarks of many local mechanics, I have found.

edit: To be fair, he made his observation when the head was off, just after we'd attached the barrel.  Seems to think the new piston is not centered in the new bore and blames the position of the crank for this.  But how he can eyeball this I still have no idea.

After cranking it over with a wrench, I think something's wrong, too, but am not convinced it's the position of the crank/rod on its own...there's a change in resistance, so maybe something's not lined up right.  My best guess now is that the bore is not perfectly straight.  Will take off the head and cylinder, check the rod's alignment against the case seam per Ace's advice, and proceed from there.  I just REALLY hope I don't have to pull the engine out again.  If I end up running with the iron barrel instead of the new alloy, so be it.  Many have before me.

Hoping against hope the crank itself is properly assembled and trued.
« Last Edit: July 08, 2012, 10:28:00 AM by AgentX »

Blltrdr

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Re: Re-centering crank?
« Reply #5 on: July 08, 2012, 02:52:59 PM »
Check the bore. Ace has posted many times on this forum explaining the correct procedure. Make sure your ring gaps are correct. Maybe find another mechanic to give you a second opinion.
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barenekd

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Re: Re-centering crank?
« Reply #6 on: July 08, 2012, 11:38:36 PM »
You need to ascertain that the two crank ends and flywheels are square.
For an initial check without removing the crankshaft from the case, check the crankshaft ends for wobbles out at the ends of the shaft. They should be turning very true, less than .002", if not remove the crank shaft and continue as below. You can also measure the gap between the wheels without splitting the case. Check the end play of the crank in the cases, too, if it's too great, that would indicate the gap between the flywheels is off, too.
If your detecting any wobble in the crankshaft ends, or the gap is too close, you need to split the case to get this part right. The flywheels need to be parallel all the way around. To check this just get a metal scale and check the lineup between the two flywheels by laying the straight edge perpendicularly across the two wheels and see that the scale doesn't have any daylight anywhere it touches. If there is, then you need to tap the wheels into trueness with a brass hammer. No chisels are necessary. Also check the gap between the gap between the swhhels and make sure it's uniform and wide enough.
But if the gap between the flywheels is too close, which is the mechanic is surmising, then the flywheels need to be spread apart a bit, but the chisel idea is not recommended on straight crankpins.  (He's taking about sticking a chisel between the rod and flywheel, the chiseling will most likely knock the flywheels out of square.) You can support the flywheel in a fixture laid up with a couple of i-beam sections and use a hammer and big drift to drive them over a bit, or out as the case may be. The chisel is mentioned for tapered crankpins, but the RE is crankpin is straight.
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AgentX

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Re: Re-centering crank?
« Reply #7 on: July 09, 2012, 02:07:28 AM »
Very much appreciate the advice.  As of now I can feel zero play in the crank from the outside. We'll see if it feels the same with the head and barrel off, and if the change in resistance is still noticeable without the top end.  Again, my money is on a bore issue, and I'm just going to change back to the bore I'd been using.  I only swapped because I had found an alloy barrel and had the engine out of the frame for a transmission swap anyhow.

However, the mechanic is, in fact, suggesting using a chisel under the timing pinion.  He truly believes the entire crank assembly simply needs to be shifted to the right side a hair within the cases, and that using the chisel will accomplish this.

I am not misunderstanding him...he's also not a "mechanic," just a guy I know.  (And whose pride may cause a scene when I tell him I'm not going to do what he instructs, which I think I can live with.) 

And before anyone says to go see a "real" mechanic, that would require taking the bike out of the city, if not the country.  I really, really wish I could.  Most of you simply would not believe this place.  A "real" mechanic is why I'm in this mess of a bike in the first place.  I'm going to do everything myself as much as possible from now on, so I really do appreciate all the assistance and knowledge you guys are passing on.  The local dealer (eschewed by most of the local riders) seems the most trustworthy and well-equipped, but also doesn't generally want to do any real machine work or measurement...just buy a new parts kit and slap it in as-is, without any further proofing.  ie, need a barrel measured or bored?  "Nope, can't do that.  Here's a new standard size piston and barrel...we'll install it for you."

You need to ascertain that the two crank ends and flywheels are square.
For an initial check without removing the crankshaft from the case, check the crankshaft ends for wobbles out at the ends of the shaft. They should be turning very true, less than .002", if not remove the crank shaft and continue as below. You can also measure the gap between the wheels without splitting the case. Check the end play of the crank in the cases, too, if it's too great, that would indicate the gap between the flywheels is off, too.
If your detecting any wobble in the crankshaft ends, or the gap is too close, you need to split the case to get this part right. The flywheels need to be parallel all the way around. To check this just get a metal scale and check the lineup between the two flywheels by laying the straight edge perpendicularly across the two wheels and see that the scale doesn't have any daylight anywhere it touches. If there is, then you need to tap the wheels into trueness with a brass hammer. No chisels are necessary. Also check the gap between the gap between the swhhels and make sure it's uniform and wide enough.
But if the gap between the flywheels is too close, which is the mechanic is surmising, then the flywheels need to be spread apart a bit, but the chisel idea is not recommended on straight crankpins.  (He's taking about sticking a chisel between the rod and flywheel, the chiseling will most likely knock the flywheels out of square.) You can support the flywheel in a fixture laid up with a couple of i-beam sections and use a hammer and big drift to drive them over a bit, or out as the case may be. The chisel is mentioned for tapered crankpins, but the RE is crankpin is straight.
Bare

Arizoni

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Re: Re-centering crank?
« Reply #8 on: July 09, 2012, 04:40:33 AM »
Just a few thoughts but remember, I haven't had a RE engine apart.
I'm looking at an Iron Barrel manual.

First off, on the drive (left) side of the crankshaft there is a ball bearing.
This bearing positions the crankshaft laterally and radially.

Because this bearing is held in place, if it is in good condition it will not allow the crankshaft to move to the side when someone tries to pry the crankshaft sideways with a chisel or anything else so attempting to move it will either have no effect or the crank case, the pinion (gear) that is being pried on, or the bearing will be damaged.

Because the ball bearing is on the drive side and the suggested prying is on the timing gear side any prying load will have to be transmitted thru the crankshafts connecting rod journal.
As you know, this journal is not an integral part of a forged crankshaft, it is pressed in  place with nuts securing it.  This area of the crankshaft was not designed to take large sideways loads so there is also the possibility that a good crankshaft might be distorted because of the forces being transmitted thru it as the chisel pries on the gear.

Typically, a good ball bearing will allow perhaps .005-.020" ( 0.12mm-0.50mm) sideways movement but no where near the .039-.078" (1-2mm) that was suggested.

Assuming the connecting rod is indeed offset to one side or the other, most pistons are designed with some clearance to both sides of the upper end of the connecting rod so that the upper end of the connecting rod does not have to be centered exactly with the pistons center.

If there is indeed a offset between the center of the connecting rod and the center of the piston, the upper end of the rod slides sideways on the wrist pin (gudgeon pin) until the potential binding of the rod disappears.  Of course there is a limit to how far the upper end of the connecting rod can move without interfering with the piston but because it was working before with the old piston/cylinder and you did not change anything in the lower end I see no reason why it wouldn't work just fine as it is.
Jim
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ace.cafe

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Re: Re-centering crank?
« Reply #9 on: July 09, 2012, 12:20:35 PM »
The crankshaft cannot be "shifted" using the method your friend recommends.
Either your crank is out of true, you have main bearing problems, or your barrel has bore problems, or your con-rod is not straight.
Home of the ACE Fireball 535 Bullet,  Ace GP Hi-Lift Roller Rocker Head Conversion. Pistons, cams, etc. Highest performance Bullet engine mods available anywhere.  AVL mods available. UCE kit coming.

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AgentX

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Re: Re-centering crank?
« Reply #10 on: July 09, 2012, 12:34:23 PM »
Once more, many thanks.

I also just thought, quite embarrassingly, of another possibility.  I am on a trip right now but will check as soon as I'm back home.

Notwithstanding my friend's odd ideas, the reason for the uneven feel at the crank may be that I have the spark plug inserted by a thread or two, to keep the hole plugged to keep bugs and dirt out...maybe it's just compression!  I will check to see if pulling the plug fixes it.  Can't recall if it tightens up on 360 degrees or 720.

barenekd

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Re: Re-centering crank?
« Reply #11 on: July 09, 2012, 06:21:23 PM »
If you don't have the valves working, ie, pushrods and rockers installed, you will have some compression on every stroke and even some resistance and the even on the downward travel as whatever air that has escaped while you are pushing the piston up, well have to be replaced as the piston travels down if you have the plug in. There will still be resistance with the plug out from ring drag. How could your friend know there was any misalignment on the rod if you have the head on the engine?
The piston is a little to the left? What the h*ll does that mean? As Arizoni says, the piston will align in the cylinder as it runs by sliding around on the piston.
I thought your friend was looking at the rod and crankshaft, I idn't read your original post closely enough. I would guess from rereading it all that you don't really have a problem. And to bang around directly on the crankshaft is not a good idea. You use the chisel between the rod and crankshaft as a wedge to pop of a tapered crankpin. The chisel end should never touch the crank!
Bare
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AgentX

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Re: Re-centering crank?
« Reply #12 on: July 14, 2012, 04:48:18 AM »
OK, I think I figured something out.  Been traveling and the bike's just been sitting there sadly for 2 weeks.

But today, I pulled the spark plug, dripped in a tad of oil, and turned the crankshaft using an open-end wrench.  Resistance was lessened with the plug out, and it turned smoothly...yet it still had distinct tight and loose spots.  (If it was a bicycle crank, I'd have said the chainrings were not perfectly round...)

I then opened the tappet chest and noticed that the tightness coincides with the beginning of movement of either pushrod.

This seems to be the "problem"...I'm just feeling the resistance and rebound of the valve springs as I turn the crank, no?

Geez.

Arizoni

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Re: Re-centering crank?
« Reply #13 on: July 14, 2012, 05:23:03 AM »
Yup.
While reading your last post I was thinking, "He's feeling the cam lobes pushing the valve's open."
No sooner had this thought occurred than I got to your comment about noticing that the resistance was timed with the tappet movement. :)
Jim
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AgentX

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Re: Re-centering crank?
« Reply #14 on: July 14, 2012, 06:28:43 AM »
Yup.
While reading your last post I was thinking, "He's feeling the cam lobes pushing the valve's open."
No sooner had this thought occurred than I got to your comment about noticing that the resistance was timed with the tappet movement. :)

Thanks.  Reassuring to hear I'm [most likely] not making stuff up to make myself feel better!  It takes me a while to figure this kind of thing out, but I guess I'm not totally hopeless.

Edit: And I fired it up today; running fine!
« Last Edit: July 15, 2012, 03:16:12 PM by AgentX »