need piston

[mr41cadillac]

i have an original 41 cadillac with 4 ring piston. i cant seem to find one so will a 3 ring piston work? if anyone has one a good used one with the bearing and rod please let me know. thanks john

[Hankk17]

maybe egge?  http://www.egge.com/

-Hank k

[mr41cadillac]

thanks i called them very friendly. i can get a set of 3 ring pistons to replace the 4 ring. will this be ok? also does anyone have experience with egge pars ? thanks

[markl]

John,
Yes, Egge parts are just fine in my limited experience, but this raises the question; are you truly looking for just one piston or are you contemplating replacing all eight?  If you did replace all 8, I'd think you'd want to go to an oversize, which are available from Egge.  But my experience has been that first you need to find out what oversizes are available and then have the block bored to the smallest oversize, just in case there is a cylinder (or cylinders) that don't clean up at the chosen oversize.

In your original post, you mention wanting a rod and the bearing as well as the piston.  Do you have the original rod?  If you do need the rod and are buying just one from a broken set, you might as well get the one intended for that position, so if that is the case, let us know what number is stamped on the rod and cap you are replacing.

I have a set of 4-ring pistons and rods but have misplaced (don't like the term "lost") the caps.  Dumb move, but that is where I stand now.  They are about 150 miles away, but I will be visiting them next week, so will check to see that they are Cadillac Standard (3-1/2") not LaSalle which is my recollection.

BTW, the reason that Egge makes and sells Cadillac Standard sized pistons is not that folks commonly install new standard sized pistons in worn blocks.  Rather is is because the LaSalle engines which were fitted w/ smaller pistons (3-3/8") can be bored out to Cadillac standard in almost all cases. 

So if you need just one piston and your machinist thinks the condition of the bore will allow a used piston's rings to seat, I can't help but believe someone will have one for sale.

Mark Lowery, CLC#25216

[harry s]

The other thing to consider is the slight variation in original sizes. The shop manual shows the identifing marks and corresponding variation in size. I like Mark also have a set of used pistons and rods somewhere to be determined. I will continue to look. Goos Luck, Harry

[markl]

John,
Harry make a good point about factory variations.  I do not have a manual for your year engine (1941).  I can only reference the 37/38 manual that pertains to the car and engine I have.  I know that some other manufacturers used various color paint dots on the interior by the pin bosses.  I see no reference to this or any other markings in the 37/38 manual.  The manual does discuss measuring  piston diameter and that is to be done at two points, both perpendicular to the orientation of the pin.  The one measurement should be "..just above the lower edge, and the other just below the lower ring groove".  From the Specification table (again the 37/38 manual), "Standard" pistons can vary as much as 2 thousandths (3.5005-3.5025").  On top of that, oversize pistons were available at .003" and .005" which I believe were intended for honed blocks, not intentionally over-bored blocks. 

So if the piston you removed was in good enough shape, I would suggest that you Mic it to see where it lands in that continuum. Another approach would be to have your machinist use an internal Micrometer to check the bore.  This should be done in any event to determine taper.  All this would help determine if the replacement piston would really fit.

Mark Lowery, CLC #25216

[mr41cadillac]

THANK YOU MARK AND HARRY. I SEE THIS MORNING that the letter h in below the piston opening on the block. the manual shows size is 3.5010-3.5012, and piston size is 3.4989-3.4991. what im trying to do is get this car running with just replacing the one piston. i dont have a micrometer but i see harbour freight has a caliper, wonder for my purposes if i could go get it and get a reading thanks john savannah ga

[markl]

John,
Don't think a caliper would do you any good in this application.  In fact what you need is an internal micrometer which you will usually see at the machinists shop stored in felt lined, fitted cases!  That gives you some idea of what they cost, and I don't think Harbor Freight handles anything of that caliber.

Now that I got the picture (car is probably at your house/shop and the engine in it) I think you have two choices:
1) Get a competent automotive machinist to come by your shop w/ his internal micrometer set and take the proscribed measurements.

2) Buy a number of used pistons, and w/ the rings removed, go through the piston fitting procedure described in the manual.  This involves sliding the piston down the bore (in running position) in the company of a feeler gauge.  Kind of a Go-NoGo test.  For the 346 V-8 in the 37/38 manual, the two gauge thicknesses are 0.002" & 0.025".  I would imagine it is the same for your engine, but sounds like you have a Manual in hand, so you are going to want to check that spec.

This brings to mind two other operations I believe you should perform.  Unless the engine had very few hours on it, you need to ridge ream the cylinder you are working on.  This is one of the reasons that a caliper will not work for the measurements you want.  And then once you've selected the piston you are going to use and fitted it w/ rings, you need to use a "Glaze-breaker" hone to prep the bore.  These are different than the hones mentioned and depicted in the factory manual.  They look for all the world like a giant bottle brush w/ dingle-balls of abrasive at the ends of the wires. They are not intended to change the diameter of the bore, but rather to rough up the bore so that the new rings (whether they are brand new or not) will seat.  Again, I would trust this operation only to an experienced automotive machinist.  Your mechanic may also be experienced w/ this operation, but all thinks considered, you only get one chance!

Now, as to the "h" stamped in the head surface of the block; that sure sounds like the fit class of the piston that was originally installed in that bore.  Hopefully, someone reading this post will chime in w/ what these letters represented and where there might be a corresponding letter stamped on the piston.  I know that on the engines I'm used to working on, the fit class markings were paint and applied on the underside of the pin boss.  Always amazed me that they would be visible and readable (true to color) after years of use in an engine.  So if Cadillac stamped theirs, those markings should still be visible after 70 years.

Mark Lowery, CLC #25216

[mr41cadillac]

mark , well my mechanic came by. he says i need a standard piston for number eight cylinder stamped h on the block. the rod was an 8 . what happened i had obliterated the 8 cutting with a dremel tool when i had tried to remove it. si if anyone has a good used or new piston number 8 with rod and bearings please let me know.