Author Topic: ST1 new cylinder and piston assembly  (Read 651 times)

RiK1200RS

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ST1 new cylinder and piston assembly
« on: February 14, 2018, 01:49:08 PM »
Today I received my brand new (original LP) ST1 cylinder and piston assembly.
Although assembling it back to the engine is pretty straight forward, I do have a question about the piston rings.

As far as my knowledge goes, piston rings have to be mounted in a certain orientation (gaps). Since this assembly was already mounted, I am not sure if I should take it apart and review the orientation (the bottom oil scraper will come out, in order to mount the connecting rod), or leave the assembly as is..
In case some of you have suggestions on the best practice regarding this, please also let me know what the orientation should be.

Thanks!


dieselgman

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Re: ST1 new cylinder and piston assembly
« Reply #1 on: February 14, 2018, 03:04:36 PM »
Original L/P no longer has the meaning it used to. You probably have India pattern parts in a Lister box. That said, there is really nothing wrong with much of the India product. The ring orientation (and actual ring design) has been simplified on the newer India sourced stuff. What used to be a stepped ring with definite top and bottom sides is now installed either way with no step and no top or bottom.

Do not assume that everything is pre-fitted. This is often not the case and you will have to make adjustments.

1.) You have to remove all the rings for checking and adjusting ring-gaps in your cylinder. (also for checking piston oil clearance in the bore). At that time you can inspect for ring markings and so on. If they have a top and bottom side, then the top will have etchings indicating such... at the least they will have a dot indicating top. Also look for any asymmetry in the ring design... this will also indicate that they will require a proper orientation.

2.) Ring gap orientation is another topic altogether... space them out evenly around the bore (about 120 degrees apart) but avoid placing them over the gudgeon pins.

dieselgman
Ford Powerstroke, Caterpillar 3304, Cummins M11, Too many Listers to count...

RiK1200RS

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Re: ST1 new cylinder and piston assembly
« Reply #2 on: February 14, 2018, 07:20:52 PM »
All clear!
Found the data needed for measuring, only the manual is not really clear about the clearance.

Under the initial clearance there are several values specified
for the ST engine.
We have :

Fire ring gap
0.70 mm
0.41 mm
0.55 mm

Compression ring gap:
0.55 mm
0.26 mm
0.40 mm

Scraper ring gap:
0.65 mm
0.36 mm
0.50 mm
(http://www.winget.co.uk/document/LISTER%20ST%20WORKSHOP%20MANUAL.pdf , page 125)

Since there are just 5 rings, the values make no real sense to me as a layman, or I am misinterpreting the values. In the SL manual (the other engine I have) the values are more clear "Between .20 and .50 mm".
Any thoughts on this?

Thanks again!

dieselgman

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Re: ST1 new cylinder and piston assembly
« Reply #3 on: February 14, 2018, 07:52:31 PM »
Pretty confusing chart they give... but use minimum/maximum figures as your range and disregard initial dimension numbers for purposes of confirming ring-fit in the bore. Don't forget to check oil clearance on the piston skirt - down in the bore. These pistons will change size as they heat up in operation. They can quickly close up that clearance and seize if they are initially fitted too tightly.

dieselgman
Ford Powerstroke, Caterpillar 3304, Cummins M11, Too many Listers to count...

vdubnut62

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Re: ST1 new cylinder and piston assembly
« Reply #4 on: March 03, 2018, 02:30:00 AM »
I will almost guarantee the ring gaps will be lined up as they come from the factory!
When I rebuilt my old International B-275 tractor with the BD144 engine "British Diesel 144 cu in" all 4 sets were perfectly fitted and gapped....
and all the gaps were  carefully aligned.
Ron
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