New Problem~PISTONS? Which ones - part #'s having a hard time locating right ones

[pooh_b_21632]

NEW PROBLEM: I have been looking all day for the proper pistons, I have the 1990 Force 120 version B that used the 3.375 pistons. I found the sierra part number 18-4632 but the picture on the website had two scoops cut into the skirt of the piston and mine does not so I called Sierra tech support and was told they did not have the replacement piston for my model he gave me the OEM number of #700-819690A1 which I was unable to find either and suggested I call wiesco. Called Wiesco and the guy at tech support said its probably the 3151PS but could not tell me for sure said he would call me back that was 3 hours ago. Found a Pro-V 5100V but cant find a picture of it.

Has Anyone with a 1990 version B or C, or a 1991-1994 replaced their pistons if so which ones did you use.

Will the 3151PS from Wiesco work if so I can get all four for 363.10 with rings and rod bearings.

 

[Frank Acampora]

Re: New Problem~PISTONS? Which ones - part #'s having a hard time locating right ones

OK! here is where it gets dicey! Cut me some slack because I don't have the actual specs in front of me and will be giving approximate numbers---here we go.

Force made two different types of 3.375 pistons. Earlier models used the force rods and wrist pins. Thes pistons were directly evolved from Chrysler.

If your engine uses a piston with rods that are about 4 1/4-4 3/8 center to center and a wrist pin with about 9/16 diameter it is old style. Additionally, the wrist pin will be centered about 1 1/2 down from the top ring land. This is because the original piston had three rings and used needle bearings in the piston to carry the wrist pin. They needed the room to get everything in. If the big end rollers are loose and held in position by a metal cage, the pistons are old style.

Then mercury got their hands on the engines. The raised the wrist pin about 1/4 inch and lengthened the rod the same amount. The wrist pin diameter was also increased. mercury did not make these changes until after 1994 so your engine is most likely an old style piston

I don't have my catalog in front of me but if the Wiseco 3151 is the old style and if you have the short rod engine it will fit. Otherwise you need the other 3.375 that Wiseco makes. As far as Sierra: If the scallops or cutouts in the piston skirt are on the bypass side, they are only there for friction reduction. However, you still need to know what engine those pistons fit.

Post a photo of your engine rods and pistons.

 

[pooh_b_21632]

Re: New Problem~PISTONS? Which ones - part #'s having a hard time locating right ones

Ok according to your calculations I have the old style short rod approx. 4 1/4 long center to center of the rod openings. Wrist pin is about 1 1/2 inches down from the top ring but I only have 2 rings not three. I do have needle bearings between the rod and piston pin. I do use metal caged bearings on the crank end of the rod. My wrist pin has three different widths the outside edges are .935, the inside edge is .800, and the diameter of the needle bearing itself is .880 .


Here is a link to the Wiesco Piston Chart http://www.marineparts.com/mpf/mpf774.aspx but it says 1991-1995 120 Crossflow (is my engine crossflow?)

Here is a link to the Sierra website http://www.go2marine.com/productcenters/sierra/sierra/8024_PDF1_V_140.pdf but the one with my diameter bore is listed for the L-drive Sport Jet and when you look it up the picture has the scallops in the skirt http://www.iboats.com/Piston-with-Rings-for-Chrysler-Force-Outboard-700-834800A4-Sierra/dm/view_id.203805


I'd rather have the Wiesco piston anyway since seems to be the better choice from reviews. (plus I can get it cheaper than the sierra) I just want to make sure its the right one before I order it and cant return it. I do know there were two size bores in 1990 version A was 3.312 Version B and C were 3.375 (mine is a version B). I think it will work since the rod size should not have changed from 1990 to 1991 right? It is listed as the right piston for the 1991 but the guy from wiesco never called me back and I didnt write his name down so I would have to start all over but I doubt he bothered to check into it anyway. I even asked if he could pull one off the shelf and measure it for me to be informed that they are not located in the warehouse, I asked if he had any specifications on it that he could tell me, his response: "yeah its a 3.375 bore". Well I knew that.

Here's a couple pictures of the third piston, the last picture is of the missing chunk, all four look similar except number one its cracked in the same spot but the chunk did not actually come out yet. Very surprising to find this without severely damaged cylinders.

 

[Frank Acampora]

Re: New Problem~PISTONS? Which ones - part #'s having a hard time locating right ones

Yep! That's the older style piston --Wiseco 3151 which is correct for your engine. I'm surprised that with the support of the ring land gone, the ring itself did not break. Your piston has a semi-keystone top ring and those are a little more prone to breaking than the flat rings. The Wiseco has a 2 degree taper ring with a better arrangement at the pin (that keeps the ring from rotating)

You will need to press out the wrist pin. No need for a cradle or special tool since you don't care if you damage the piston or needles. With the Wiseco, you must buy new needles (bearing kit) for around 12-13 dollars but in my opinion, their forged pistons are far superior to cast ones and worth any extra money they cost. The wrist pin held by circlips is a blessing for assembly too.

You misunderstood me when I wrote about three rings. The OLD Chrysler engines had three thick rings and a needle bearing in the piston wall on each side of the wrist pin. (1960s). The wrist pin was pressed into the small end of the rod. It was heavy and had more drag. In addition, the wrist pin had to be low in the skirt to leave the room for all those parts. Later on, they went to your two ring design, but because changing molds and forging equipment is expensive, they retained the short rod.

The one thing that Merc did in the late 90s that I really agree with was to lengthen the rod and raise the wrist pin in the piston skirt. This is the Wiseco 3164 piston which you do NOT use. While it will fit in the 3.375 bore, nothing else is the same and it will not work.

Since the original design came from West Bend engines, you have an engine with "Old School" 40 year old engineering. It is dead standard crossflow and there is nothing wrong with that--it produces horsepower and gets you across the water. It's just that newer designs produce more power from the same size engine and use a bit less fuel.

 

[pooh_b_21632]

Re: New Problem~PISTONS? Which ones - part #'s having a hard time locating right ones

Ok thanks, BTW that 363.10 for all four pistons includes rings and bearings not a bad deal huh? anyway Mr. Pooh has a friend lending him a dial caliper to check the bore inside tonight I only hand a hand held caliper to check the edge dimension and Id rather check it now then find out opps later. If all looks ok tonight I should have my new pistons next week will update as I go along.


I actually love this engine; easy to work on, lots of get go (even though I had a bum engine from the start I never got over 4,000 RPM WOT now I know I should have been able to get 5,000-5,500 easy), and its easy on gas. before this one we were using my in-laws 115 evinrude on a grady white (not much power) didn't go half as far and used twice as much gas. I can run this one for hours up and down the river taking the kids tubing and usually use less than 5 gallons. Most I ever used in one day was 12 gallons and that was like six hours of tubing. That averages out to like 2 GPH even at the cost of gas today can you take 3 kids to an amusement park (have that much fun) and spend less than $30 including drinks and snacks, not a chance. Plus the boat ramp is a hop-skip-and-jump from my house

 

[pooh_b_21632]

Re: New Problem~PISTONS? Which ones - part #'s having a hard time locating right ones

Just wanted to add an update for anyone searching the forums looking for answers as I was doing before posting. I found several post that were on the right track for me but no one ever posted a fix so I figured I would be nice.

Yes the Wiseco 3151PS Pistons were the correct ones for my 1990 Version B Force 120 engine. Cheapest Place to purchase them at the time I bought mine was http://www.boatpartstore.com/forcesearch.asp?cat=itemname&cval=3&hval=38&val=119# s piston, rings, pin, and circlips for 1 cylinder was $84.79

Helpful hint pay someone with a hydraulic press to press your pistons off for you I recieved my pistons some time ago and it took about three weeks to finally get the rods out of the old pistons. I tried hammering them out (several times), I made a piston puller, I tried a vise, and I bought a 6 ton bottle jack press from Harbor freight which my husband proceeded to break, then a friend with a repair shop tried his 12 ton bottle jack press with no luck, another friend had a air driven hydraulic jack and had less trouble and got them all four off in a short amount of time.

Once I finally got the rods off and the new pistons on (BTW use a silver permanent marker to mark on the rod which way is up before pressing the old pistons off) I started trying to put it back together. I tried putting the bearings onto the crank first then putting the piston and the cap in I tried for some time but every time I would get the bearings on then put the piston in the bearings would slide on top of one another and after a while I broke one of the cages (they are expensive). Finally I figured it out. I took ATP-201 transmission assembly lube blue and put it onto the rod, put the bearing cage onto the rod and put the bearings into the slots. I gooped it pretty good so it would stay put. I bought a ring compressor from Pep-boys for $8 bucks and compressed the rings, centered the crank and gently pushed the piston into the cylinder so it hooked onto the crank. Then I slid the rod cap in through the reed openings with the bearing cage and bearings gooped onto it as well lined it up and pushed it forward gently with a screwdriver. I used a 1/4 inch ratchet with a long extension and a 1/4 inch 12pt socket and a swivel to put the bolts in. The swivel is essential to getting a good tight fit I did it several times without the swivel and the rod was still loose and I had to take it apart fix the bearings and start over. So save yourself the trouble and use the swivel. I torqued them all to 190 (check twice just to be sure). Once I got them all seated I spun the engine by hand about two dozen times to get them good and seated and check the torque again just to be sure they were all tight.

Hope this helps someone, Good Luck!