Pistons for a 1998 75 Force

[TwoFish]

Looks like I need a rebore and new pistons for my 1998 75 hp Force. The bore was quite worn although not damaged or grooved. It had a substantial lip at the top which is too large to remove with a hone.

I’ve looked around and have found a couple of places selling Wiseco pistons. One listed the kit as containing “Rings, wrist pins, wrist pin bearings and retainers” and the other didn’t mention the wrist pin bearings. I'd like to order the correct parts first time.

A couple of questions.

1 Are the wrist pin bearings needed or usually part of the kit?

2 When fitting new pistons what happens to the needle bearings at the wrist pin end of the con rod? Are they reused or is there a different type of bearing used with the Wiseco pistons? I'd like to know how to fit the new piston to the old rod.

I hope this is the last surprise the motor has for me.

Thanks again for the help.

TwoFish

 

[jerryjerry05]

Re: Pistons for a 1998 75 Force

Will Wiseco send to AU?
I've found most sell the "extras" on the side?

 

[Frank Acampora]

Re: Pistons for a 1998 75 Force

I don't have my Wiseco catalog in front of me. However, I think your 75 uses the Wiseco 3151 piston (3.375 bore standard). It comes complete with piston, rings, wrist pin, and retaining circlips in standard, .010, .020, .030, and .040 overbore. The STOCK piston very likely uses a pressed-in wrist pin with two press fit keepers. Later model Mercury built engines MAY use circlips--I don't remember. The 75 was a bit of an oddball engine.

The Wiseco 3151 piston uses a slip fit wrist pin retained by two circlips. Because the Wiseco pistons have thicker wrist pin bosses, the stock keepers will not fit inside the piston, over the wrist pin. Thus, you must buy the W5216 bearing kit. It comes with two slip fit spacers and new small end needles. While the needles are the same size, you MUST use the Wiseco spacers to retain and center the needles in the small end of the rod.

If your engine uses a different piston, It may not need the bearing kit.

 

[TwoFish]

Re: Pistons for a 1998 75 Force

Thanks for the replies.

Frank. I spoke to the Australian dealer for Wiseco and they said I needed a 3164 kit which is fine but they don’t make a bearing kit for the later model Forces. He said I would need to contact marine part supplier and get the bearings from them.

What I trying to work out is what I will need . The bearing kits that comes with the other Wiseco pistons consist of spacers and needles. I am assuming that the standard spacer and needles will work with the Wiseco pistons for the later model Forces. I can get these easily.

1. Do I need to put a gauge on the small end of the con rod to check for wear to ensure that new needles and pin will not have too much play? I would have thought the tolerances would be very fine. I looked through my manual but can’t fine a spec for this measurement.
2. Are the con rods so hard that they are not likely to wear?
3. If the old needles and spacers look OK will I need to replace them?

I don’t want to start ordering parts and find out I have missed something. I have never done this before so I’m being cautious.

I’d like to thank everyone for the help as I would not be able to tackle this on my own.

Thanks

TwoFish

 

[Frank Acampora]

Re: Pistons for a 1998 75 Force

As I said, I was not sure about the pistons. If you need the 3164 kit, go with that.

Small end needles get very little movement and a lot of oil. They very rarely wear. The rods are dead hard and again, they don't wear. The only damage I see on rods is bent rods from a lock-up, wear from bad bearings that have shed steel particles, and rust.

SOME piston kits do not need the bearing kit and if the 3164 is that type, simply re-use small end needles if they are still good. You will immediately see bad needles --lots of steel colored oil and pitting. If Wiseco does not make the bearing kit, that means that you will not need to order the W5216 kit. What you have now should fit. Dang-- I wish I had my catalog in front of me.