gx160 with flat top piston

Full Throttle

Full Throttle

Member
#1
#1
Just bought a Z4M flat top to go in my gx160 but trying to decide which billet rod to use. .010 over or .020 over or stock on the rod length ? Haven't put piston in yet with stock rod to see how deep in hole it is but was wondering if anyone else has already tried this and can add some light as which rod to install. All help appreciated !
 
Prowler08

Prowler08

New Member
#2
#2
Best to put the stock Rod on with the new piston and see...
The Z4M has a slightly shorter comp. height... So you might need a longer rod...
If I remember right with gx160 was .005 in the hole with the dished piston with the Z4M piston you might end up .010 in the hole.
 
vwfan79

vwfan79

Active Member
#3
#3
I have a few gx160s with this piston, a .010 over rod will put you flush with the deck. Make sure you get the right rings they are different from stock, and it's a good idea to run a hone through the cylinder to get a new cross hatch for the new rings to seat.
 
Full Throttle

Full Throttle

Member
#5
#5
Thanks VW .Does this Z4M piston take the thinner rings ? I think the stock rings are 1mm thick but correct me if i'm wrong. Still waiting on piston to arrive. Also does the piston install like you have in your pic with dot up or does it matter ?
 
Motra

Motra

Active Member
#7
#7
It does matter. The piston pin is offset to reduce piston and cylinder wear on the major thrust side. The mark on the piston is supposed to be positioned towards the push rods.

 
Motra

Motra

Active Member
#9
#9
I've actually heard of engine builders who install the piston backwards for some kind of performance gain but I'm not sure of the reasoning behind it. Something to do with reducing piston speed at higher RPM I think. You might research that and find out you're not so wrong after all.
 
Full Throttle

Full Throttle

Member
#10
#10
Well got my Z4M flat top put in this evening and checked the piston to the deck with the stock rod in and came up with .030 in the hole. So gonna get a .020 over billet rod and still be .010 in the hole. Feel better about where the piston is now. Local shop told me to have piston .005 in the hole but like the .010 gives me a little more room when i mill head .050 with a black mamba cam. Now just gotta check valve to piston clearance and hope to get somewhere around .080 to .100 clearance with the right head gasket. Hope i'm right ?
 
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