Used P&C #'s

[NoEardGoat]

I just got a set of used pistons and cylinders for my rebuild. They look clean and the walls look as if they have already been re-touched with a hone. They came with new rings, but some of the numbers like the piston to cylinder clearance scare me a little.

Pistons
# Weight Top Ring Mid Ring Oil Ring
1 596 1.6 1.78 3.51
2 595 1.58 1.78 3.52
3 593 1.58 1.78 3.5
4 596 1.58 1.78 3.49
5 597 1.6 1.78 3.52
6 599 1.6 1.78 3.49
D1 D2
1 94.958 94.958
2 94.948 94.948
3 94.955 94.955
4 94.953 94.953
5 94.96 94.96
6 94.953 94.971

Cylinders
# Size Ht Group Ht
1 1 6 85.41
2 0 6 85.42
3 1 6 85.41
4 0 6 85.43
5 0 6 85.41
6 1 6 85.44
D1 D2
1 95.024 95.029
2 95.026 95.014
3 95.024 95.019
4 95.034 95.037
5 95.039 95.039
6 95.039 95.029

Cylinders
D1 D2
95.024 95.029
95.026 95.014
95.024 95.019
95.034 95.037
95.039 95.039
95.039 95.029

P to C Clearance
CL
1 0.0685
2 0.063
3 0.0625
4 0.0825
5 0.079

Should I go ahead, balance and use these with the new rings?

Experts please chime in!

[2.7RACER]

Your pistons and cylinders are designed to run with a .025mm clearance when new.
Since we are in the US lets talk American.
That's one thousandths of an inch.
Your pistons are worn an average of one thousandths from new.
Your cylinders are worn an average of one thousandths from new.
Therefore the average piston to cylinder clearance is 3 thousandths.
The manual says the wear limit is 5 thousandths, That's .12mm.
Book says replace the cylinders if the wear is more than 3 thousandths from new, .08mm.
Insert a new compression ring. Book says the end gap should be 8 to 16 thoudsandths of an inch, .2mm to .4mm.
Book also says, if the end gap is over 31 thousndths of an inch, .8mm, replace the cylinders.
Based upon this, your pistons and cylinders are half worn out. They'll work ok, new would be better, you knew that.
I'd be sensitive to the end gap with a new compression ring installed in the cylinder. If it is close to 31 thousandths, I'd consider using other cylinders with less wear.
I'm sure others may have an opinion that may differ. I'm just going by the book.
Good luck,

[NoEardGoat]

thanks Doug!!

What book are you going by. I couldnt' find the wear limits in wayne's rebuild book, but havent' checked the Bentley manual.

[2.7RACER]

Bentley

[aigel]

Can't you machine the rings to modify (enlarge) end gap?

George

[cnavarro]

You could have the piston skirts coated, to close up the piston to cylinder clearance. From time to time I'll redo a set of cylinders back to stock with stock pistons for various reasons and I always have Calico Coatings coat the skirts. They just charge a little more if they need cleaning, that's all. They end up looking like new, and in my experience, i've seen engines with tens of thousands of miles still have their skirt coatings in place.

[NoEardGoat]

Skirt coating sounds like an interesting idea. How much would something like that cost?

This pistons do have some marks from valve lash in the top, but I was told this wouldn't affect anything, as the weights can be matched.

I feel much better after reading the Bentley manuals specs. The only number I really worry about is the piston to cylinder clearance, which could be resolved with the above suggestion.

I need to clean the pistons up a little better, and really clean up the outside of the cylinders. Any suggestions on materials, and solutions. Maybe; Mineral spirits, berrymans carb dip (very strong), brakeleen, scotch brite bad, sand blast?

Emerson

[cnavarro]

Having the piston crowns, ring lands, and skirts coated runs about $300 once you figure in freight to and from Calico. They can also coat the wrist pins, which I have done a few times now, and have been pleased. Makes everything have the fit and finish of brand spanking new!

I pass the buck on cleaning the cylinders usually - the platers usually acid dip and blast the cylinders, which destroys the plating, but hell, they are replating them. I have had Calico clean and coat exterior areas with their thermal dispersant, but only on 356 cylinders where we are trying to go for the look of the original coated alloy barrels.

[aigel]

If you do want to clean yourself, I had good luck with cab cleaner. Just dip the whole piston in overnight and you'll be all set. A ring land cleaner will be mandatory as well. You want it to look like new, when you are done.

George