1946 59a Mercury standard bore 3 3/16 pistons

[Phil Gillespie]

So had a little oil consumption problem with 59a Engine which had recently been rebuilt be an engine reconditioner.
Have pulled all pistons and just measured uo No1 piston.
Plenty of side clearance at top 2 piston rings as well as rings also have a step ridge. Top ring side clearance 12 thou 2nd ring side clearance 10 thou
Top ring thickness: 87/75 thou 2nd ring thickness: 88/80 thou.
So have located the cause of oil consumption.
On plus side bores are good still standard without ridge.

Would it still be adviseable to hone bores. Dont really want to remove c/shaft.
Please see a picture of the piston note the slot between oil rings.
This passes right through piston skirt. What is the purpose of this. Cant see any make on pistons.

Thanks
Phil NZ1946 Mercury piston No 1 001.jpg

1946 Mercury piston No 1 002.jpg

[JSeery]

There was a resent thread on this same topic, you might check it out. Myself, I would not hone an engine with the crank in place, too easy to contaminate not only the crank but the rest of the engine. However, there are some that claim to have done it successfully.

[Ol' Ron]

This is an Auto-Thermic piston. It has a steel strut in it to contain expansion. It is fit with tight piston to wall clearance (.0005/.0015) The slot controls the expansion. The ring stack on a piston is usually .020/.025" smaller than the skirt. not sure about the ring grooves. Ring side clearance is usuall very tight .004 /.006
I have ground a crank in the block on one throw, flushed the bearings and oil passages with kerosene/ 383 Chrysler . drove it for another 20K

[Phil Gillespie]

Originally Posted by Ol' Ron

This is an Auto-Thermic piston. It has a steel strut in it to contain expansion. It is fit with tight piston to wall clearance (.0005/.0015) The slot controls the expansion. The ring stack on a piston is usually .020/.025" smaller than the skirt. not sure about the ring grooves. Ring side clearance is usuall very tight .004 /.006
I have ground a crank in the block on one throw, flushed the bearings and oil passages with kerosene/ 383 Chrysler . drove it for another 20K

Ron, thanks very much for all that info. An Auto-Thermic piston more new info for me. are these pistons still sold? Has the standard top two ring grooves at 3/32 and oil grooves at 3/16.
Am inclined to go with a new set of standard Egge pistons and new ring set. Then light hne with 249 grit ball hone. Yes?
Phil NZ

[Fordestes]

I have in the past taped off the crank journal and put oily rags under the cylinder being honed ,after the honing ,washed the cylinders with kerosene and then solvent or hot soapy water, after the cylinder cleaning I used a siphon blow nozzle to flush the crankcase and clean the crankshaft oil holes, then wiped clean with a lint free cloth, the hone grit and crosshatch pattern is important , hone accordingly to the ring material and the ring manufacture recommendation.

[Phil Gillespie]

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What is recommended side clearance at ring to ring grooves.
Depends upon piston and rings in use?
Phil NZ

[cadillac512]

Originally Posted by Phil Gillespie

What is recommended side clearance at ring to ring grooves.
Depends upon piston and rings in use?
Phil NZ

Ford spec is .003"-.004" for ring side clearance in grooves. Check closely to make sure they aren't tapered wider at the outside.

Any obvious cause why the recent rebuild had this problem? Dust?



Terry

[leon bee]

I don't understand yet why it was burning oil.

[Phil Gillespie]

Originally Posted by leon bee

I don't understand yet why it was burning oil.

Too much side clearance at rings to piston groove also could see the build up above top ring and carbon build up on piston crown.
The rings i removed had a ridge of approx 10 thou at top ting and 8 thou at 2nd ring. Ring width at outside edge 87 thou but 75 thou at step.
This was where the oil was going. Also bore is good nil lip but no sign of and cross marks from hoing.
What is said to have been done and the actual reality are different.
Phil NZ

[Phil Gillespie]

Originally Posted by leon bee

I don't understand yet why it was burning oil.

Too much side clearance at rings to piston groove also could see the build up above top ring and carbon build up on piston crown.
The rings i removed had a ridge of approx 10 thou at top ting and 8 thou at 2nd ring. Ring width at outside edge 87 thou but 75 thou at step.
This was where the oil was going. Also bore is good nil lip but no sign of and cross marks from hoing.
What is said to have been done and the actual reality are different.
Piston ring grooves are not bad: Top : 95 thou 2nd: 94 thou 3rd: 186 thou 4th 187 thou. Standard 2 top are 3/32 and bottom 2 are 3/16.
maybe just need a new set of rings.
Phil NZ

[cadillac512]

Phil- What was the end gap on the compression rings?



Terry

[Phil Gillespie]

Originally Posted by cadillac512

Phil- What was the end gap on the compression rings?



Terry

35 thou way too much!!
Phil NZ

[Ol' Ron]

Most manufactures used Auto thermic pistons during the 30's thru the 50's. Thanks for the .004" side clearance, I wasn't clear on that. Memory takes a vacation every once in awhile.

[flatheadmurre]

What´s the actual boresize ?

[Phil Gillespie]

Originally Posted by flatheadmurre

What´s the actual boresize ?

Still awaiting some telescopic bore gauges to arrive to measure accurately.
My vernier at top of bore nil ridge apparent is 3.1878 approx.
Phil NZ

[cadillac512]

It's quite odd to see this much increase in ring side clearance due to ring wear without a lot more end gap than .035". Also strange to hear the ring grooves measure in spec. It'll be interesting to hear how the bores measure up.

Makes a person wonder if a bunch of used parts from various engines were assembled. Please keep us informed,Phil.



Terry

[flatjack9]

[QUOTE=Phil Gillespie;1859457]Still awaiting some telescopic bore gauges to arrive to measure accurately.
My vernier at top of bore nil ridge apparent is 3.1878 approx.
Phil NZ[3.1875 would be .060 over. For every .001 increase in diameter, the end gap will increase a little over .003.

[Ronnie]

Originally Posted by Phil Gillespie

35 thou way too much!!
Phil NZ

Take that same ring and measure end gap at the bottom cylinder where the rings don't run.


R

[Ol' Ron]

If this was my engine, I'd bore it to 3 5/16, use Egge 3 ring pistons. Angle mill the heads .060: Use a Dremel to make piston to head clearance, same with valves. End result would be : increase of torque in the low and mid range , and better economy. Especially with a SBC distributor. Just use the stock cam and valve assys.

[Phil Gillespie]

Originally Posted by cadillac512

It's quite odd to see this much increase in ring side clearance due to ring wear without a lot more end gap than .035". Also strange to hear the ring grooves measure in spec. It'll be interesting to hear how the bores measure up.

Makes a person wonder if a bunch of used parts from various engines were assembled. Please keep us informed,Phil.



Terry

Without a doubt this seems to be the case. The restoration and engine "rebuild" took place over many years and believe now used parts were indeed used.
Phil NZ