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Author Topic: Aligning piston and liner  (Read 1856 times)

Offline Geoff Goodworth

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Aligning piston and liner
« on: August 03, 2017, 08:09:01 PM »
I have to rebuild a Brodak 40 which was running really sweetly until a crash ripped the muffler off, taking the back muffler lug with it.

Can anybody suggest a clever way too ensure that the piston and liner are in the exact same places when reassembled given that there isn't a little pin to align the liner like in OS engines?
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Offline Chris Wilson

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Re: Aligning piston and liner
« Reply #1 on: August 03, 2017, 08:21:05 PM »
Scribe a line going across the top of the liner to the engine casting before disassembly.
Realign upon assembly.
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Offline Geoff Goodworth

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Re: Aligning piston and liner
« Reply #2 on: August 03, 2017, 09:03:32 PM »
Thanks Chris but two things—

1.   The top of the liner is the gasket face.

2.   Its a new crankcase so the only possible reference is the bolt holes or something on the outside of the case.
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Offline Air Ministry .

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Re: Aligning piston and liner
« Reply #3 on: August 03, 2017, 09:40:46 PM »
If you got a bleedy great liquid marker pen , and put a hairline scribed across the piston crown & liner top lip , thatd give you a ' in line ' orientation on assembly , if its not already apart .
If yoyu wernt washing it or suchlike before fitting .

Id use a straight edge & knife tip , carefully .

A FLASHLIGHT with a good battery , into the Ex Port , would put some light on things . Normally a stain on the liner ,
so getting it centralised in the exhaust cut out / hole , should be effective .

Or give up & give the pieces to ME .  ;D S?P

 H^^
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Offline Tim Wescott

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Re: Aligning piston and liner
« Reply #4 on: August 04, 2017, 09:35:23 AM »
If it's like most engines the liner sticks up from the case when it's fully in.  So scribe the outside of the liner, and the case.
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Offline Fredvon4

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Re: Aligning piston and liner
« Reply #5 on: August 04, 2017, 10:15:15 AM »
Guys all good advice but it sounds to me like he is transferring his used Piston liner into a NEW case

Geoff
Just make sure on the original engine the relative Exhaust opening of the front and rear liner positions and make then the same in the new case...going to be just a good eyeball TLAR install

I would probably carefully scribe the top of the piston and a small scratch on the liner and in the new case, once the rod is on the crank clock the liner to be TLAR identical to the piston top and make sure again that the exhaust port is near same orientation in the new case



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Offline Geoff Goodworth

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Re: Aligning piston and liner
« Reply #6 on: August 04, 2017, 10:56:26 PM »
OK guys, here's what I've done.

First I put screws in the front and rear head screw positions and used a ruler and a fine Sharpie marker to draw a line to the edges of the screws.

However!

Having disassembled the engine with minimum trouble—the tolerances are very fine—I cannot get the liner to press into the bore of the new crankcase.

Should these be so tight that I need to expand the crankcase to get the liner to slide in?
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Offline Air Ministry .

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Re: Aligning piston and liner
« Reply #7 on: August 05, 2017, 08:35:32 PM »
A certain individual mentions sanding the case bore with 320 Wt. paper . so the liners a light press fit .  :-X

Id get a michealometer on it first / virneer . to see if it just being awkward .

Heat case & drop liner HALF in , see if the piston still fits in the bottom of sleeve , cooled . If it sticks ,
sand the bar#*%# . After reheating & attempting to remove the liner .  S?P
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Offline phil c

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Re: Aligning piston and liner
« Reply #8 on: August 06, 2017, 10:00:16 AM »
Given the kind of damage, torn off muffler lug on the case, it's fairly likely the case and liner were  bent in the crash.  The cylinder may be not truly round.
On the other hand, if the liner slid fairly easily out of the case, and/or could be rotated while in the case, that indicates that the new case has a smaller I.D.  You really can't fix that by hand.  I'd suggest that after making sure the piston and liner are still round send the new case back and ask to have the liner used to select a different case that fits.

The best way to fit the case requires machine tools such as a lathe or mill.  A half way good way to do it is to have someone with a honing machine open up the case diameter so the sleeve slides in without the fit being too loose.
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Offline Brian Gardner

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Re: Aligning piston and liner
« Reply #9 on: August 09, 2017, 06:28:08 AM »
If I remember correctly the B40 is AAC. Whatever you do ...do not heat shrink the liner in - you'll never get it out.
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Offline Phil Krankowski

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Re: Aligning piston and liner
« Reply #10 on: August 09, 2017, 07:03:20 AM »
Quote from: Brian Gardner on August 09, 2017, 06:28:08 AM
If I remember correctly the B40 is AAC. Whatever you do ...do not heat shrink the liner in - you'll never get it out.

Why not heat/cool?  Seems a small temperature change would be all it takes.

Pop the liner in the fridge for an hour and see.

Phil
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