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Little end shimming for piston guided rod

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Currently in the process of building a VW Polo GTI engine (engine code AVY). With the standard pistons the rod is guided by the piston to keep the big end floating in the center of the journal, the little end has 12 thou clearance between the bosses in the piston. We are putting it together with Wiseco pistons and K1 rods (WKE254M77AP, 043EJ09138), with this setup the gap between the bosses in the piston is a lot bigger, in the region of 6-8mm clearance between rod little end and piston bosses which means the rod is free to float on the big end journal with around 4mm clearance between the crank webs. The crankshaft has an annular groove at the edge rather than a radius, with the bearings centered in the big end and the rod pushed to one side of the journal the bearing passes over the annular groove by 2.02mm. I have tried to contact Wiseco and K1 and havent had a response yet as to whether the float is acceptable or whether I need to shim the little end to reduce the float and keep the bearing centered on the journal. Has anyone ever heard of this needing to be done and if so what would you recommend using to shim the little end. I have added a video showing the amount of float that I am talking about.

Thanks in advance.


Attached Files

I would suggest changing the rods or pistons to get dimensions that match. I suppose if it's a race engine you are going to be rebuilding every 50 hours, you could make wrist pin spacers (I would probably make up some aluminum ones and have them hard-anodized) and keep an eye on them.

It would seem either Wiseco or K1 screwed up on the product they sent you. How does the little end dimension compare to the OEM components?

If you can't get it resolved with the party at fault supplying the correct part, you will have to do something like David suggested - the hard anodising would be expected to minimise galling/pickup between the spacer and the piston bosses, but I'm not a metallurgist, so get some advice in case there may still be a problem.

Thanks for the replies. I have managed to find out from Wiseco and K1 what the issues are. Apparently the pistons and rods are semi generic across the VAG range of engines and what Wiseco and K1 used to do was send out a set of shims/spacers with the different piston sets with a fitting guide that told you which shims/spacers were needed for each engine set up. Unfortunately the person that used to send out the shims/spacers since left and they no longer send them out or manufacturer them. I have been told that they used aluminium for the shims/spacers but have not given me any dimensions for them other than I need 0.2 - 0.25mm clearance on the little end. I am going to go down the aluminium shim/spacer route and like you both said get them hard anodized to prevent/minimise the galling/pickup. Think its going to be fun times ahead trying to measure the clearances between the little end bosses and little end of the rod. Was going to use playdoh and see what the clearance was between the little end and the boss when I pushed the rod over to each side, I know what the float is so should be able to work out the shim/spacer size required for each side of the little end. Unless anyone has any easier/better ways to carry this out.

Thanks again for your help.

Can't you use a bore gauge, or simple snap gauge to measure between the piston bosses, and a micrometer to measure the small end width - then subract the latter from the former to get the clearance?

That's hopefully the process that I'm going to use, But I'm not 100% sure that the little end sits perfectly central in between the pin bosses of the piston and was hoping to be able to measure it all in situ. Think I'm going to make two equal shims to start with and then work from there if the big end needs to be pushed either way to sit it central on the crank journal.

that is a crazy thing to be not told about when purchasing them. best of luck '

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