Piston cleaning, too clean??

[rothfm]

I've cleaned a set of std crossflow 115hp pistons. soaked them for days in Berrymans (the not-so-toxic) Walmart can. Over a week I got them all clean, mostly by painstakenly and slowly rubbing, and picking the carbon off with nylon brushes and picks. Lots of work.

Man, they are clean...Super clean....Should I be worried about any prior "coatings" on the skirts, or piston head? They've been mic'd good and I'm about to install them with new rings, but wanted to check about any issues with being too clean looking. They are all shiny aluminum all around.

 

[racerone]

Post pictures of these pistons.--Ring grooves and areas where measurements were taken.---Include the measurements too.

 

[rothfm]

Will do, and post up in the morning...Thanks.

 

[emdsapmgr]

The old factory crossflow service manuals describe cleaning and measuring (mic'ing) of pistons for possible re-use. They specifically call out cleaning of the ring grooves with an old broken ring (to eliminate carbon accumulation,) checking ring end gap in the block and measuring the pistons and cyl walls for (over) size, taper and roundness. If the measurements are within factory tolerance and the pistons clean, you should be ready for re-assembly. If the rods are off the pistons, make sure the oil hole in the rods face upward during re-assembly onto the pistons.

 

[F_R]

Depending on the year, some of the old crossflows had tin-plated pistons, and made a big deal of it in their advertising. However, I was personally told by a factory engineer that the tin plating was mostly to help get it through the break-in period on 50-1 oil. I don't know if the Berryman's would remove tin plating or not. Or if it was ever there on yours.

 

[rothfm]

Ive measured according to the OEM book, and am familiar with rebuilds. I typically replace pistons, but I now have an assortment and picked 4 of the best, and carefully cleaned and measured them. Hoping so save some dollars. These will have new wrist pin/bearings, as well as new rod bearings/cages.

Diameter at 1/4" above botttom edge at several locations 90deg from each other shows 3.4933 and 3.4941 within specified .004 difference.

Square ring groove side clearance(lower) is below the .004in spec at appx .0032

The upper pressure back groove ring when seated, allows a straight-edge to touch the piston on both sides of the groove- in spec.

Some of the tops appear a slight brown hue, while others are more shine. Maybe I'm just nitpicking...Overall they appear nice, I still have to get a couple of flecks of carbon off still.

 

[Bosunsmate]

I dont normally bother with the little or big end bearings due to the costs of doing them all.
Was there a failure that has led to this rebuild or are you reconditioning her?
If you are this meticulous with the pistons what are you doing to the bores?

Cleaning out the ring grooves as mentioned above is what i focus on in rebuilds

 

[emdsapmgr]

The other critical measurement are the cyl liner bores. How is the taper on them? Are they eggs-shaped? Are there any signs of scuffing or vertical scratches that won't hone out? See attached pic of a typical damaged cyl liner.

 

[F_R]

I wouldn't hesitate a bit on using those pistons.

 

[rothfm]

This all started with me removing and disassembling the swivel bracket-big job.(new seals and bushings) then resealing the TNT. I had the powerhead off to repl the base gasket, Then I re-hosed it and put on new engine-side harness. Thru the port covers, I found stuck rings. Compression was in the 100-105 range. I remember having up to 120-125.

So Decided to break apart the case to measure and remove all carbon. Both myself and a shop measured the bores for overall, roundness and Taper- on the outside of range but in specs. No visible issues, so I lightly honed. All looks pretty good.

Going to forge ahead, and put it back together. Was just curious if others thought I was nuts since it was all apart, to not repl pistons. I'm a cheapo to a point.

 

[emdsapmgr]

A hone job and new ringsets and you should be good to go. I've done the exact thing before.

 

[Bosunsmate]

A hone job and new ringsets and you should be good to go. I've done the exact thing before.

Thats what i mostly do

 

[rothfm]

Thanks for the feedback Folks. I'll start putting back together if we ever stop Shoveling snow here near Boston. Getting ridiculous now!