Another head question
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Joined: May 2020
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From: Oklahoma
Another head question
On my 83 shovel, progressing through the rebuild. I removed the cylinders and pistons. I am taking them to the machine shop to have them "miked". I don't have a bore gauge. I did mike the pistons and both the front & rear mike out at 3.495 at 90 degrees to the pin. The front piston has a " 4 B" marking and the rear piston has a " 6 B" marking. My understanding is the "B" marking is the grind. Don't know what the 4 & 6 designate, other than location. ?? The bike probably is a 7.4:1 compression ratio. The pistons look in great shape, so waiting to see what the machine shop says after inspection. I just soon reuse the pistons and cylinders if all is well. 7.4:1 is pretty lame, but ...
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From: la la land jerzey
The numbering system is in house factory for grading and sizing on assembly line - common stuff
had you pictured up and asked the guys would have given an opinion to re use with just ball honing and moly ring set
had you pictured up and asked the guys would have given an opinion to re use with just ball honing and moly ring set
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Joined: May 2020
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From: Oklahoma
No, I am using the info from my service manual. It list my bike to have 7.4:1 compression ratio. I have no idea what the cranking compression is. I did a cold cranking test (psi) before tear down. I didn't do a leak down test. The front cyl was 90 psi & rear 100 psi. When I pulled the cylinders, the front piston had a broken compression ring (top ring). There is no scoring on the cylinder. Not sure when that happened, but after examining both pistons, I can tell there is a bit more carbon build-up on the ring groove and ring on the front piston. I can send pics, but not sure what profile of pics to send. I have cleaned the pistons with scotch brite pads and have removed most of the carbon.
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