Stuck a piston

[Morris85C]

Mike Ive seen this happen a 100 times or more sense Ive been racing. Its fixable. You have my number An really sorry to here about your dog.

[David_L6]

Nothing new. I've seen pistons relieved at the wrist pins. Ask Dudley Malone or Paul Christner about it.

[blueskyracer]

Now I have a matching set.. Anyone need a ash tray? I really want to get this sucker going cause when it runs it is a monster right up to sticking

[Steve77t]

Now I have a matching set.. Anyone need a ash tray? I really want to get this sucker going cause when it runs it is a monster right up to sticking

That thing is to tight at the top of piston from the wrist pin up as Rex suggests

[Morris85C]

Are those VORTEX PISTONS

[PRO-MOTIONRACING]

I would chuck up the wrist pin in a lathe and emery cloth it if I wanted a little more clearance in the wrist pin bearings. I think it would be a lot easier.
Larry Mac

Sounds good Thanks.

[blueskyracer]

Are those VORTEX PISTONS

Yes Lonnie they are Vertex pistons..

[Morris85C]

Thats what i thought Mike give me a call

[blueskyracer]

Thanks for all the info last night Lonnie.. It makes sense and it is not the first time a manufacturer has changed the original formula

[pops67g]

Afew more thoughts...

After seeing your pictures something crept back into my memory. Several years ago I heard a racer from out east talking about repeated problems such as yours. It took 5 times before he woke up. He was using aftermarket pistons as you are. The problem was due to a couple of things. The first was probably some mickey-mouse alloy that wanted to puff up like a balloon when heated. The second was that the ring land area on these pistons was the same diameter as the skirt. When all the heat is put into the piston crown the ring lands expand too far and scuff. The cure is to chuck up the pistons in a lathe and turn down the ring lands. I don't know the optimum dimension on this but there is probably no magic number here. Turn them down .015 or so and it still gives good support to the rings.

[ZUL8TR]

well trying to get use to a empty house I went and worked on motors.. Got the stuck piston one apart and I was right it was number two this time.. I did some measuring of the bores and they all seem to be 2.579-2.580 and the pistons measure 2.575 at the skirt and 2.571 at the piston pin boss area.. My question is can I hone out a thousandth or two to give more clearance..

I did a compression check on the motor the daughter was running and suddenly shut down.. Cylinder one was 120, cylinder two was 50, cylinder 3 was 120, and cylinder four was 65.. I guess I will be tearing down another engine..

At least engine number three is all 125 for compression but it got very hot when I shut it down and was really surging so I am glad I shut it down and got to use the tow rope again.. That one I think I lost the water pump so that's another repair.

Based on the numbers you measured the skirt clearances are 0.004 to 0.005".
Here is a piece of Harry Brinkman's manual on modding Mercs. For Class E Mod (44 ci) he recommends 0.0075" for hot filler block and 0.007" to 0.009" for cold filler block. Based on this it appears the clearances you have are too tight and you are right to want to open it up. Might be a bit much for a hone but depends on the hone. The penciled edits are from Harry's correction page as they appear on the Boatsport.org page where the full manual is located.

When I was refreshing my 25ss 22 ci to 0.015" over + other stuff I was coordinating with Jerry Wienandt on parts and many helpfull details. He prefers the Mercury 44 ci 2 ring pistons. Said they are very well made, dimensionally accurate, weigh darn near the same and excellent aluminum composition. Used them at recommended clearances and no stick.

[Dave M]

Vertex

Seems I have heard of a couple folks having some issues with those pistons.... You may have found your problem. Maybe it was a bad batch, maybe it is simply poor material, or poor engineering for that particular model piston.

Lonnie won't steer ya wrong, he knows his stuff as well as anyone.

[Rex Hall]

Piston clearance

From what I see of your pistons, there is no rubbing or gauling at the intake or exhaust side of the piston. The skirt clearince is not the problem here, the piston does not have enough cam grind at the wrist pin and above. I would not hone the cylinders bigger, I would set the pistons up and give more clearince from the bottom of the wrist pin to the top, only at the wrist pin area. You can take your stuck pistons, remove the rings and using a new flat bastard file, file all the hard glazed part of the piston down to where you have at lease .005 more clarance on each side of the wrist pin. This will allow for the piston to expand without rubbing so hard that it sticks and will keep your skirt clearance to get good crankcase compresion. I cannot see the inside of the piston, but if you counter bore the boss above the wrist pin, it will compensate some of the expansion at the wrist pin area. I am not just talking here, I have made hundreds of pistons for Mercurys, Yamato's, Konigs, Quincy's, Hot Rods, Evenrudes, Rossi's ect.

[Guest]

Bore size

What you need to do is get a bore gage so that the full length of the bore diameter is known. Normal glaze breaker hones tend to taper the bore. From what I see you might have a temperature issue along with setting the clearance to tight. I like a loose engine so .008" to .010" clearance would be great. Another thing that might be tried is to use Mercury 44XS pistons to see if they work better.
E bay has a number of new bore gages in the $100 range. The picture is of one listed for $145 with free shipping.

Alan

[ZUL8TR]

bore gage

What you need to do is get a bore gage so that the full length of the bore diameter is known. Normal glaze breaker hones tend to taper the bore. From what I see you might have a temperature issue along with setting the clearance to tight. I like a loose engine so .008" to .010" clearance would be great. Another thing that might be tried is to use Mercury 44XS pistons to see if they work better.
E bay has a number of new bore gages in the $100 range. The picture is of one listed for $145 with free shipping.

Alan

Alan

Looking at the number on that gage it reads to 1 part in 100,000. That is huge accurate, digital gages have a calculation scheme in the chip so some +/- must be in the gage reading calculation. What does the spec sheet state for +/- on the reading?