Author Topic: Big end clearance  (Read 12850 times)

Mucke

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Big end clearance
« on: December 25, 2008, 10:46:04 PM »
Merry Christmas everyone,

today I installed the plain shells John sent me on my 12/1
The journal is perfect and it measures 2.496-7 (63.43-6) on a new digital caliper.
I have no way to measure the mounted and torqued shells inner diam and i cannot get hold of plastigauge.
The original shells had 3 shims with together 0.02 thickness (o.5mm).
Both shells fit nice and tight between the crank s shoulders.
I decided to leave the shims away and torque without them.
There was no visible and "feelable" slack , the crank moved easily  by hand and after dismounting the
shells show no sign of scratching.

How can I tell if I have enough clearance ?

Thanks
Rolf

rcavictim

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Re: Big end clearance
« Reply #1 on: December 25, 2008, 10:54:29 PM »
Got any thin radio-tv solder (60-40 lead-tin) or make up a sliver of plumber's lead solder.  Use this like plastigauge but measure the crushed thickness, not the width after crushing as that is not calibrated.
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oliver90owner

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Re: Big end clearance
« Reply #2 on: December 25, 2008, 11:59:35 PM »
Rolf,

If it is free it has enough clearance.  Your problem may be too much clearance.

If I was worried about excesive clearance I would insert a piece of shim material and carefully tighten the rod bolts, carefully checking for free movement and being careful not to damage anything.  The clearance should be less than 3 thou.

Also check for bearing nip.

Regards, RAB

Mucke

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Re: Big end clearance
« Reply #3 on: December 26, 2008, 10:54:25 PM »
Thanks,
didn't know lead wire was practicable as a gauge.
by the way, what is bearing nip ?
Rolf

Stan

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Re: Big end clearance
« Reply #4 on: December 26, 2008, 11:58:20 PM »
Don't use acid core electronic solder for crushable measurements, it will damage your bearing surfaces.  Get the solid stuff.  You can read about bearing nip at rocketboy's site.  He has a manual online that you can read all about it.  I'd type it all out (I did somewhere in the distant past here on the site, but it's a long description and you can read it yourself.  http://www.f1-rocketboy.com/lister9.html   goto page 14

Stan
« Last Edit: December 27, 2008, 12:00:53 AM by Stan »

rcavictim

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Re: Big end clearance
« Reply #5 on: December 27, 2008, 12:08:19 AM »
Don't use acid core electronic solder for crushable measurements, it will damage your bearing surfaces.  Get the solid stuff.  You can read about bearing nip at rocketboy's site.  He has a manual online that you can read all about it.  I'd type it all out (I did somewhere in the distant past here on the site, but it's a long description and you can read it yourself.  http://www.f1-rocketboy.com/lister9.html   goto page 14

Stan


Stan,

Acid core solder is not used in electronic work.  The only acid core stuff I have ever seen is the fat stuff about 1/8"+ diameter and that is too big for what we are discussing here anyhow.  You may have a point however.  Perhaps some of the fluxes used may be harmful if residue is left on the bearing or machined crank surfaces.  Simple solvent wipe with a soft cloth should take care of this however I'd think after the measurement.

BTW, it being Boxing Day today the title of this thread seemed quite appropriate!   ;D
-DIY 1.5L NA VW diesel genset - 9 kW 3-phase. Co-gen, dual  fuel
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-Changfa 1115
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-Want Lister 6/1
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Stan

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Re: Big end clearance
« Reply #6 on: December 27, 2008, 12:38:12 AM »
You're absolutely right, I meant to type Rosin core solder and yes you can clean it off with some sort of solvent but you have to know that you need to do it.  I'd bet a beer that "raw" rosin would bugger up a bearing if left on.

Some .75mm would give you a good idea of crush.
Stan

matt

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Re: Big end clearance
« Reply #7 on: December 27, 2008, 09:52:21 PM »
This thread has started at the right time for me.

I installed my new big end bearing with the 2 shims in place.

There was not any up-down looseness movement - it seemed ok here. Not too tight to inhibit normal required movement.
However, when I tried to tilt the con rod left to right there was movement - enough to be a few mm either side when you look at the small end.

This tilt is a pendulum type of movement and not an entire left right movement.

Should I be worried about this?

Matt 

oliver90owner

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Re: Big end clearance
« Reply #8 on: December 27, 2008, 10:53:01 PM »
Should I be worried about this?

Yes.

Movement at the small end will be magnifying the clearance to the small end but 'a few mm' means little to me.  Need a definitive check on that clearance.

Regards, RAB

Stan

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Re: Big end clearance
« Reply #9 on: December 27, 2008, 11:01:19 PM »
Matt....I agree with Richard, it is NOT GOOD for a big end bearing to have any noticeable movement.  Goto your local autoparts store (FLAPS, friendly auto parts store) and buy some plastigauge, it's cheap, easy to use and gives fairly accurate readings where nothing else can work.
Stan

lendusaquid

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Re: Big end clearance
« Reply #10 on: December 28, 2008, 12:52:33 AM »
Matt
How thick are your shims? If they are Indian shims then they could be way to thick.Shims can be made out of any old beer or coke can.
Take the shims out and torque up.If its tight then add one shim and try again.Keep adding shims evenly to both sides untill the rod moves without binding.

Mucke

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Re: Big end clearance
« Reply #11 on: December 28, 2008, 01:45:49 PM »
You're absolutely right, I meant to type Rosin core solder and yes you can clean it off with some sort of solvent but you have to know that you need to do it.  I'd bet a beer that "raw" rosin would bugger up a bearing if left on.

Some .75mm would give you a good idea of crush.
Stan

Stan,
page 14 of the original manual you mention says 0.075 mm or 0.003 " for the crush.
0.75 mm must be 1 order to big.

I'll make the solder test today. The "nip"  with the big end around the crank seems o.k.
Too much crush probably ! Even without those 3 shims.
What shall I do ? Alu foil between conrod bore and bearing ?

Rolf

mobile_bob

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Re: Big end clearance
« Reply #12 on: December 28, 2008, 05:41:31 PM »
a simple method to get you into the ballpark if you have a micrometer and can't get either plasigage or
some lead wire.

find a piece of paper that is about .003" and place it between the big end brg and the journal
then see if the rod will move, if it locks up you have less than .003, if it moves freely you have more
if it barely moves you have approx .003"

if you measure various pieces of paper you can find .002, .003 and thicker without much trouble.

20# typing paper is about .004" iirc, i would expect paper from a phone book to be under that
and the flimsy yellow pages maybe down to a bit under .003" but use your micrometer to determine what it is.

bob g
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Stan

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Re: Big end clearance
« Reply #13 on: December 28, 2008, 07:22:47 PM »
Yup, at .75mm it's big enough to "crush" down and let you then take it out and measure it with a micrometer.  Make sure you put a couple of pieces almost all the way around the bearing so you can tell if it's round.  If it's not round, you will see the crushed solder clearly shows its spread wider where it's is tighter and narrower where the bearing is looser.  Test it in a couple or 3 different places too.  Don't try and turn the flywheels when you have it tightened down.
Stan

Mucke

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Re: Big end clearance
« Reply #14 on: December 28, 2008, 09:36:34 PM »
O.K., I have tried it with fishing lead shot.

I choose 2 small balls of 1.9 mm diam.(.075") and fixed them with a drop of oil parallel to the lower shell's oil groove.
Torque and yes, I did some turns on the flywheel to feel the resistance.
There was some now!
Disassemble and find them squished to 6 mm across (1/4 ") and .11 mm thickness  (.004 ")
Both nice and same picture.
They did leave a mark, though in the babbit! Won't do any harm, but it shows lead is not plastigauge ...
From  the depth of the mark I can guess that the clearance is .075 mm o.k.
Torqued again and pins into the castles.

I made some pics but I am too silly to upload them into the Lister Engine Gallery.
If anybody wants to see them, help me.

Rolf