Possible bent rod

[Johnwesley]

 Checking deck height on an engine, what's the tolerance side to side on the piston, directly above the wrist pin? I'm showing 0.004 different on this engine rear cylinder. I'm thinking possible bent conrod

[Pirsch Fire Wagon]

What Engine?

[kd]

What method are you using to measure?  What are you using to hold the barrels down and what sequence did you use to torque them down? 

[Johnwesley]

95" twin cam. Using the short head bolt with spacers. Torqued bolts to 20ftlb x pattern, using depth gauge. The bottom o-ring left in. All 4 short head bolts used.

[kd]

I'd be tempted to loosen off and re-torque but start with the studs on the side that measures the closest to the deck.  see if the difference changes sides. The crankcase halves are known to not match up well and that can cause an issue like you describe.  I think there was a Tman video here a few years ago where he demonstrated the mismatch and decked the surface of the assembled halves to true them up.  It may be on his web site.


Here it is.  You can probably find a way to check yours.

https://www.youtube.com/watch?v=sD0ON4Aa7KQ&feature=youtu.be

[Johnwesley]

Thanks man i'll Give that a run

[Norton Commando]

Perhaps the top of the piston is not parallel with wrist pin bore.

Jason 

[Don D]

The pistons rock. Measure across the pin axis. A thousandth or two difference side to side is common. average that number.  When you get a large difference side to side it could be a bent rod but this is not a common twin cam occurrence. It can be checked with engine in the frame.

Comparing a bottom up build when all the original machine work is checked and tightened up isn't exactly fair. The factory is sloppy compared to what a decent shop can do. When I bore cases they all get resurfaced. Cylinder height varys some and that is easy to fix. The pistons, even stockers, are decent as far as compression height tolerance.

[Johnwesley]

The pistons rock. Measure across the pin axis. A thousandth or two difference side to side is common. average that number.  When you get a large difference side to side it could be a bent rod but this is not a common twin cam occurrence. It can be checked with engine in the frame.

Comparing a bottom up build when all the original machine work is checked and tightened up isn't exactly fair. The factory is sloppy compared to what a decent shop can do. When I bore cases they all get resurfaced. Cylinder height varys some and that is easy to fix. The pistons, even stockers, are decent as far as compression height tolerance.

Thanks, it's only a few thousandths. I did check across the wrist pin when I measured. I decided to go with a 0.030 hg and leave the cylinders as they are which should make a street friendly 190ccp 9.2 corrected compression. With decent squish. The other option would be machine and hope my measurements are spot on, if not risk 27 thousandths and possible piston head contact once carbon builds up some.

Perhaps the top of the piston is not parallel with wrist pin bore.

Jason

I'm having that checked at the machine shop.

[HD/Wrench]

not uncommon to have a piston that is not in line with wrist pin to keep the terms simple . JE is a great example of this . Its not the hugest deal in the world though . get it the best you can and move on still a tractor engine John

[Hillside Motorcycle]

Checking deck height on an engine, what's the tolerance side to side on the piston, directly above the wrist pin? I'm showing 0.004 different on this engine rear cylinder. I'm thinking possible bent conrod

You can easily check for a bent rod with a precision dowel thru the wrist pin bore, and precision parallels on the case deck, using feeler gauge/shim stock to verify side/side differences.

[Johnwesley]

I'd be tempted to loosen off and re-torque but start with the studs on the side that measures the closest to the deck.  see if the difference changes sides. The crankcase halves are known to not match up well and that can cause an issue like you describe.  I think there was a Tman video here a few years ago where he demonstrated the mismatch and decked the surface of the assembled halves to true them up.  It may be on his web site.


Here it is.  You can probably find a way to check yours.

https://www.youtube.com/watch?v=sD0ON4Aa7KQ&feature=youtu.be

Got everything back and rechecked it and as you assumed I must of had the jug slightly loaded on one side more than the other. It all checks out square. The machine shop did verify the piston top was parallel to the bore. So zero decked and ready for the heads.

[kd]