SuzukiSavage.com - Print Page

SuzukiSavage.com
/cgi-bin/YaBB.pl
General Category >> Rubber Side Down! >> Wrist Pin Fit
/cgi-bin/YaBB.pl?num=1310269985

Message started by verslagen1 on 07/09/11 at 20:53:05

Title: Wrist Pin Fit
Post by verslagen1 on 07/09/11 at 20:53:05

Does anyone know if the wrist pin is supposed to fit in the con rod?
tight but free to rotate?

I got one that took some effort to get out.
A new pin won't go in w/o a persuader.

Title: Re: Wrist Pin Fit
Post by justin_o_guy2 on 07/09/11 at 23:48:12

Something has to let the piston rock on the con rod, I sure wouldnt want that to be at the piston/wrist pin end of it. I woulda thot the wrist pin would fit nicely in the con rod & be maybe a bit more snug in the piston.
Having to hit it to get it in the con rod seems wrong to me,,

Title: Re: Wrist Pin Fit
Post by Oldfeller on 07/10/11 at 03:18:38

Does the wrist pin fit correctly in the piston?

If so, lightly tap it into place and go on with life. The fit is supposed to be a snug one and somebody's tolerance slipped a bit (or else if it is Wisco replacement pin they are attempting to go print max to take up for rod end wear in in the typical engine their stuff goes into (an older engine).

If you have to beat it into place, that is too much. Lightly tap in place isn't bad as that is considered "correct fit" in some engines. Make sure it is evenly spaced on both sides (does not load the ring clips).

It should be able to drift side to side slowly over time as the engine seats itself in .....

Title: Re: Wrist Pin Fit
Post by Routy on 07/10/11 at 05:31:26

I'm the first to admit I don't know this engine,... but as in any engine we know it must turn, either in the piston or the conn rod, and maybe both. And whichever it is, it must have space for oil, or it could gall.
There is no standard in automotive engines. Back in early years, 60-70, ford used the "both" method, meaning the pin was a push fit in both the piston and the con rod,....using clips in the piston to retain the wrist pin.
SB Chev on the other hand, chose to use a press fit in the conn rod, letting the wrist pin float freely in the piston,.....using NO clips in the piston whatsoever. Both methods worked well,......except the ford method was very critical in getting a good close fit in the conn rod.
In those days a tap fit was considered not enough clearance for oil to get to the surface that must be free to rotate (rock).

Title: Re: Wrist Pin Fit
Post by Oldfeller on 07/10/11 at 07:15:27

Those with loose wrist pin to small con rod end with snug to piston fits do all the rocking at the small end of the con rod. This is a bad idea using hardened steel on steel, most of these type set ups have a needle bearing on the wrist pin/con rod.

Those with snug fits to con rods and loose fits to piston do most of the rocking at the piston (steel pin in aluminum).

Some bike engines allow both, until the steel on steel at the con rod eventually varnishes up or galls up tight anyway -- then the rocking all takes place steel on aluminum at the piston.

I can't speak for all Savage engines, but the ones I have been into allowed rotation (with some resistance) at the steel on steel con rod junction. It was a tight fit but it could rotate. I suspect most of the rocking action still takes place at the pin/piston joints as the area loading is a lot less and they are dissimilar metals with an oil film to keep them from galling.

I always clean the varnish off the pin and the inside of the con rod. Perhaps you have a bit of varnish build up inside the con rod? Mebbe a little galling too?

Title: Re: Wrist Pin Fit
Post by MotoBuddha on 07/10/11 at 07:56:32

When I installed my Wiseco piston, using the wrist pin that came with it, was a very close fit, but I could push it in with my thumb once everything was properly aligned. I had to remove the wrist pin, and I was able to push it out with a finger. When installed, the piston rocks freely on the connecting rod. I can't tell whether it's pivoting on the piston, the rod or both. Of course, that's with everything cold. Once things heat up and the various metals expand, who but an engineer is to say how things end up fitting.

Title: Re: Wrist Pin Fit
Post by verslagen1 on 07/10/11 at 08:14:54

Thanks for the input.
Looking at the pin in the wiseco piston, the wear pattern indicates that it rotates in the piston most.
I polished out the bad spot in the con rod and tapped the pin into place.

Title: Re: Wrist Pin Fit
Post by Boofer on 07/10/11 at 09:52:27

The wrist pin should rotate and the piston has to, also if I remember. but it should have no wiggle in the perpendicular. It also should slide in the piston. Thus the oil holes in the piston around the pin. A sloppy fit of either will give piston slap and not run as far. BE SURE to grease or oil well during assembly. Boofer

Title: Re: Wrist Pin Fit
Post by MotoBuddha on 07/10/11 at 12:26:16

705D5D545740320 wrote:

I just checked my old stock piston and wrist pin, With the retaining clips in place, the wrist pin will move end to end about 1/16 inch.

FYI, here's what the wear pattern looks like on my stock wrist pin:

http://i280.photobucket.com/albums/kk182/motobuddha/957c2704.jpg

Title: Re: Wrist Pin Fit
Post by Boofer on 07/10/11 at 16:26:15

That's right. I know of a local Harley that let the pin slide out enough to ruin the cylinder. The quote for parts was, according to his brother, over $1,000. :'(

Title: Re: Wrist Pin Fit
Post by MotoBuddha on 07/11/11 at 07:17:36

I don't know how Harley pistons are designed, but as you can see with the stock LS650 piston, the wrist pin is recessed into its hole, and the ends of the holes are recessed from the diameter of the piston. The retaining ring would need to come out before the wrist pin could touch the cylinder. I suspect HD pistons are similar.

http://i280.photobucket.com/albums/kk182/motobuddha/b51d5f61.jpg

As you can see, the Wiseco piston used for LS650 big bores is even narrower at the wrist pin.

http://i280.photobucket.com/albums/kk182/motobuddha/da201ef7.jpg

Title: Re: Wrist Pin Fit
Post by Routy on 07/11/11 at 07:49:55

I just read,.....
.0002 is minimum clearance needed for oil in a wrist pin. That is much less than a half thousanth,.....or,....2 ten thousanths !
I believe that would be about a push fit, like most pins push into a piston. I would think that a tap fit in the conn rod would be less than that,....and not enough room for oil, and therefore designed for the rocking to take place in the piston,.....kinda like a small block chev, only they were a couple thousanths press fit into the conn rod, so that there was no chance of the pin moving to the cylinder wall.

Title: Re: Wrist Pin Fit
Post by Boofer on 07/11/11 at 08:03:29

I appreciate the comments on how it should be, but sometimes things don't work right. That is why most people come on here asking for help. I took my car to a guy who told me his wife's car never had the problems mine had, so I'm thinking, "Okay, I'll go to someone with an open mind to look for all the probablilities and then run through the impossibilities." BTW I have a friend who is running a small block Chevrolet I put together ten years ago. Bored .030, .010-.010 on the crank, recon rods, torker intake, Holley carb, Manley springs, Racer's Warehouse push rods, etc. When I was around 21 I took my brother's Kawa 90 jug off and found needle bearings on top of the piston. Bought rings, wrist pin and a little creative sanding by hand. But no, that couldn't happen.

Title: Re: Wrist Pin Fit
Post by justin_o_guy2 on 07/11/11 at 08:07:37

Sometimes, man,, things just go sideways,,

"Ya win a few & ya lose a few, Pilgrim".

You guys know who said that?

Title: Re: Wrist Pin Fit
Post by SURAZAL on 07/11/11 at 10:32:53

remember the piston and con rod are both aluminum and the wrist pin is steel Coefficient of expansion for AL is 3 x what it is for steel so the assembly should not be more than a light thumb press fit tight and they will open up as the engine warms ups and will generate the correct funning oil clearance.