Piston and wrist pin replacements - Merc 800

[Moody Blue]

Hoping to get some clarification on replacement pistons and wrist pins. Have been working on refurbishing a 1971 Merc 800.

Have been researching replacement pistons for this motor. Merc has SOOOOO many different part numbers for the same piston that I'm not sure what I should/could be looking for. Can I assume that any of the 2.875" pistons from the early 70's in-lines (4 and 6 cyl) should be compatible? Is there a cross reference list of some sort?

I'm not clear on the whole issue of wrist pin and piston pairing.

1)Can a wrist pin be removed AND reinstalled into the same piston? I want to replace the needle bearings.

2) Can a wrist pin be installed into a DIFFERENT piston from which it was removed? Have read that they should not be, BUT how are they originally married as a set at the factory? What is the harm in interchanging wrist pins? Inquiring minds want to know.

3) I have two piston assemblies where the wrist pin is loose in the piston. What are my options?

 

[Faztbullet]

Re: Piston and wrist pin replacements - Merc 800

Have been researching replacement pistons for this motor. Merc has SOOOOO many different part numbers for the same piston that I'm not sure what I should/could be looking for. Can I assume that any of the 2.875" pistons from the early 70's in-lines (4 and 6 cyl) should be compatible? Is there a cross reference list of some sort?

HEE-HEE..this will confuse ya!!! There are (6) types of pistons...high dome, low dome ,3 land, 2 land, ported and non-ported. The 3 land pistons O.D at top of ring land measure different at ring land (2.857) than 2 land pistons (2.863) due to 3rd ring. Also note that there are 2 types of rings and the 3 land and 2 land rings will not interchange. There are also different reed petal designs(see below) and reed designs(8/10 and 10/10 petal)

1)Can a wrist pin be removed AND reinstalled into the same piston? I want to replace the needle bearings.

Yes and wrist pin does not need to be full removed, if removed mark the side with a sharpie and pin also..

2) Can a wrist pin be installed into a DIFFERENT piston from which it was removed? Have read that they should not be, BUT how are they originally married as a set at the factory? What is the harm in interchanging wrist pins? Inquiring minds want to know.

No.....wrist pins hammer into the piston bosses over the years that why you dont mix and match as they mate each other......

3) I have two piston assemblies where the wrist pin is loose in the piston. What are my options?

It not usual to have some loose , they should slide in and out snugly with no axial play..... new piston you can push in wrist pin with fingers.

 

[Moody Blue]

Re: Piston and wrist pin replacements - Merc 800

It not usual to have some loose , they should slide in and out snugly with no axial play..... new piston you can push in wrist pin with fingers.

Not clear on what you are saying Faztbullet.

Of the pistons I have, two of the wrist pins slide back and forth between the snap rings in the piston boss. There does not seem to be any "slop", just a sliding motion. The wrist pins in the other two pistons seem locked in place.

If I can get my hands on new wrist pins, can they be used in the old pistons?

As for the pistons, I have the three land, non-ported type. Not sure if they are high or low dome types. What alternatives are available for replacements? I've searched for the original P/N's (745-3561) but have not come up with any sources.

 

[buzzm19]

Re: Piston and wrist pin replacements - Merc 800

MB, I have a cd mercury manual and it covers 4 & 6 cyl mercurys from 75 to 79 but the mercurys from older years as mine (1971-1972) are basically the same animal. In my cd manual and of course using the tool to drive the wrist pin in, it states to heat the top of the piston to 190 degrees F then tap the pin in with the tool as the tool will center the pin in the piston. In my day of racing and using full floating pistons the wrist pins were held in by special piston retainers and the wrist pins had .0001-0003 clearance max and any more end play of the wrist pin and the wrist pin could act as a battering ram and possibly knock the retainers out. When I was working on my 1972L6 those wrist pins are pressed in and I could clearly see that those wrist pin retainers are not nearly strong enough to hold the wrist pin in the piston and also there is way too much play in that assy. If they were made to be loose then the end clearance would be like I stated earlier and the retainers would be much stronger. Any time I bought pistons in the past and now the piston and pin come as a matched set. Check out serria marine catalog there website is great and to browse it is a dream, they are a little pricy but I found out that you can see the pictures and if the part numbers have been changed. Buz