A few questions about rebuilding a pro 800 motor.

[machinest660]

I just tore down my 2011 pro rmk motor to install the mtnk fix kit. the engine had 1400 miles on it with 105lbs compression. The pistons were in great shape with no scoring and the same with the cylinders. The cylinders show no signs of cracking. The rings did show some flaking. When I measure the stock pistons I noticed that they were a bit tapered. they measured 3.339 on the bottom and 3.327 on the top. The measurements on the cylinders were 3.345 on the top and 3.349 on the bottom. This would give .010 clearence on the bottom and .018 on the top. Can anyone confirm the bore size for me when the cylinders are new? Are they have a taper from new?? The new mntk pistons measure 3.325 which is .002 smaller then the factory pistons that were in there. As far as i know this motor has not been torn apart but I am not the original owner so who knows for sure. Sorry if this has been posted before but i did a search and came up with nothing. Thanks

 

[machinest660]

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[rmscustom]

Cylinder measurement should be 3.3465'' and you should be measuring your pistons at the skirt. What did you use to measure the cylinders?

 

[machinest660]

Cylinder measurement should be 3.3465'' and you should be measuring your pistons at the skirt. What did you use to measure the cylinders?

Thanks for the info. I used a inside mic to measure the bores and confirmed that measurment with the outside mic I used on the pistons. The bottom piston measurement was on the skirt. I will have to remeasure the mtnk pistons tomorow morning casue they were measured at the top I think.

 

[beamslayer]

Should use a bore gauge to measure cylinders that way you can check for out of roundness also . If you are using snap gauges and transferring to mikes it takes a special touch and some practice IMO to measure correctly .

 

[rmscustom]

Should use a bore gauge to measure cylinders that way you can check for out of roundness also . If you are using snap gauges and transferring to mikes it takes a special touch and some practice IMO to measure correctly .

Agree, that's why I asked.

 

[machinest660]

I used a inside mic not telescopic gauges, I agree a bore gauge would be best but i didnt have one on hand. With 12 years trade time as a journeyman machinest and a journeyman millwright i hope i have the special touch lol . I checked everything over this afternoon and its all with in spec, ring gap, piston clearence and cylinder size once i measured the pistons in the proper spot. Gonna be gone working for a few weeks now so wont have any progress for a while, thanks for all the info guys,

Should use a bore gauge to measure cylinders that way you can check for out of roundness also . If you are using snap gauges and transferring to mikes it takes a special touch and some practice IMO to measure correctly .

 

[Lococoin]

Cylinder measurement should be 3.3465'' and you should be measuring your pistons at the skirt. What did you use to measure the cylinders?

Where did you get that measurement from? I dont see anything in the manual that says anything other than 3.34. The MTNTk fix kit instructions say that if you need to replate the proper bore is 3.347.