cylinder/piston codes
 

I am trying to understand how you can mix/match pistons and cylinders.
The pistons come in group weights and seem to be in size ranges as well - matched presumably to variances in production tolerances in cylinder sizes, which also seem to come in group heights.
Have I got that right?
if that is correct does that mean that cylinders and pistons need to come as a matched pair? And cylinders need to be matched in group heights - at least per side of engine. But if your tolerance bore size was different, you would have a different group weighted piston?
I am trying to understand if I can replace one damaged piston or cylinder etc if I need to.
There is a partial set of new pistons/cylinders F/S in my country at the moment. But if I bought them as spares, am I able to source the matching cylinders and pistons?
Anyone follow this?
Thanks
Alan

Alan,
The cylinders have deck height and size stamped on them. The deck is either 5 or 6 inside of a triangle. You need the same deck on the same side, preferably all 6. The size match the piston.
The pistons are sized according to size. Basically, 0, 1 , and 2. The pistons have weight castings in side the piston usually look like ---/++. What the actual pluses and minuses mean I dont know and they dont always set with the same + and- in a set.
Thats what I know and dont know...
Bruce

OK, thanks Bruce, making progress.
So the deck is the number in the triangle.
Any idea where the size number is - and does that correspond to the piston sizing number , ie a 0,1 or 2 for the piston and cylinder.
whats the bet a piston weight is either above or below a nominal weight (+ or - ) by nominal increments ie -- meaning two increments below?
Do you know if you can buy specific sized individual cylinders/pistons, ie how do you deal with one damaged piston, eg a damaged ring land where the other 5 may be fine?
Alan

If you ve lost a piston and cyl you need to match the dech height and the size and the type. There is piston ID on the inside of the piston, such as 95P36 for Mahle or 95160 for KS. These numbers tell you exactly what the piston and cyl is and in the case of 2.8 tells you if you have Mahle alucil or nikisil, its all in the piston number.
Bruce

I'm trying to work out whether to purchase this partial set as spares. Where would I find a source to provide the rest of the set if I have the numbers in the bottom of the piston?
Any idea?
It seems like a tough ask for someone to supply the right group weighted and sized piston with the correct cylinder height and sized cylinder? Do they only come in complete sets?
Alan

Alan

PM me for used pistons and cylinders.

I can likely find a good used match for you.

Here is a listing of piston types.

http://forums.pelicanparts.com/uploa...1312417263.jpg

Hi Tom, Thanks.
What I'm trying to get to the bottom of is what you are trying to match when putting a set together.
Match deck height - 5 or 6 on the cylinder. I get that bit.(lining up heads and CR)
What about cylinder/piston size groups 0,1,2,3 - is it necessary to match that as well?
Then there is the group weight. The 930 manual says you can be out by 8 gms with an individual piston, but groups are +/- 2gm. So, do you match size groups and live with 8gm variances or ignore size groups and try and balance pistons?
I have a chance to buy 5 new P/Cs for a 930 and trying to work out where to go from there given 5 is not a particularly useful number.
Interestingly your chart quotes 930 CR as 7.5
Regards
Alan

Alan

Here's what I do to assemble a matched piston cylinder set:

1. Make sure the cylinder ht groups are the same on each engine bank. Either all (6) the same ht group or (3) of one ht group and (3) of the second ht group.

2. Weigh each piston and make sure the difference between the lightest and heaviest is less than 8 grams

3. Check the ring land end clearances to make sure they are in spec. The top compression ring land takes the most wear and is most critical

4. Measure the piston diameters perpendicular to the wrist pin axis, about 1/4" below the wrist pin. This requires a precision micrometer

5. Measure the cylinder bore diameters at top and bottom stoke locations, at 90 degrees apart (4 measurements). make sure the cylinders are not worn beyond spec diameter and that the ovality or difference between the largest and smallest diameter does not exceed 0.4mm. This requires a bore gauge calibrated to the same micrometer used for the piston measurements.

6. I then plot the diameter data and match large and small pistons and cylinders to obtain piston to cylinder clearance less than 0.10 mm

Here is an example copy of the plot and data sheet I use.

Hope this helps


http://forums.pelicanparts.com/uploa...1312458489.jpg

Tom,

That is a very good explanation of your measuring and selection process, I getting ready to do this soon, thanks.

Regards,

Wade

OK, Thanks Tom. I have the gear - micrometers , bore gauge etc. Just been thru that process checking over my track engine last week since I re ringed it.
You seem to have 2 piston diameter measurements - are these just duplicates?
Since you seem to be mixing/matching P & Cs, I presume there is a source of these individually?
Alan

Alan

The two piston measurements are repeats.

I can supply most of the pistons in my listing above and also have spare cylinders available.