Abnormal piston to cylinder tolerance??
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Road Warrior
Joined: Jun 2015
Posts: 1,325
Likes: 140
From: Edinburgh UK
Abnormal piston to cylinder tolerance??
Hi All
Well I pulled the heads to get them ported and skimmed to 10:1 cleaned up the cylinder tops and the pistons till they are spotless, tightened but not torqued the cylinders down and measured the deck height ...this is what I found...
Machined straight edge across the top front to back and the piston is down (above the pin) 0.008" but, the piston is tilted in the bore - deck height at the front of the piston is 18 thou at the front and 2 thou at the back !! Cylinder bores look normal and can still see the honing and no sign of scoring at all.
I can actually feel the piston move left to right (on the pin) a touch when at TDC and with it to one side I can easily get a 6 thou feeler gauge between the piston and the bore down to the top ring at the other. The service manual says to replace the piston if more than 3 thou gap piston to cylinder.
Bike is a 2014 softail, 103, with only 8500 reasonably gentle miles. Is this right? (or typical anyway). Oh, and is 8 thou a bit excessive for the deck height, think I read 5 was typical?
cheers for any thoughts
Well I pulled the heads to get them ported and skimmed to 10:1 cleaned up the cylinder tops and the pistons till they are spotless, tightened but not torqued the cylinders down and measured the deck height ...this is what I found...
Machined straight edge across the top front to back and the piston is down (above the pin) 0.008" but, the piston is tilted in the bore - deck height at the front of the piston is 18 thou at the front and 2 thou at the back !! Cylinder bores look normal and can still see the honing and no sign of scoring at all.
I can actually feel the piston move left to right (on the pin) a touch when at TDC and with it to one side I can easily get a 6 thou feeler gauge between the piston and the bore down to the top ring at the other. The service manual says to replace the piston if more than 3 thou gap piston to cylinder.
Bike is a 2014 softail, 103, with only 8500 reasonably gentle miles. Is this right? (or typical anyway). Oh, and is 8 thou a bit excessive for the deck height, think I read 5 was typical?
cheers for any thoughts
Banned
Joined: Sep 2009
Posts: 3,569
Likes: 624
From: deland,florida
pistons are tapered,with the top being smaller than the bottom.pistons are measure at the bottom of the skirt with a micrometer,cylinders are checked with TQ plates & bore gauges.when checking deck hieghts,check at the wrist pin as the piston will have some rock front to back.if you are concerned,i would remove the cylinders and check them properly
Thread Starter
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Road Warrior
Joined: Jun 2015
Posts: 1,325
Likes: 140
From: Edinburgh UK
Cheers guys, I never noticed this before until I was measuring the deck height for setting the compression ratio
still learning, thanks
Edit: the 8 thou was definitely in the middle over the pin by the way so happy I got the right measurement
still learning, thanks
Edit: the 8 thou was definitely in the middle over the pin by the way so happy I got the right measurement
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