OK need some assistance here.
I am in the middle of a rebuild. Took the engine to pieces and delivered the head and jugs to a machine shop where they honed the cylinders. Bloke told me that they had taken .0036 out of the original spec and that I would need to buy rings to suit.
The first picture below shows the top of one of my original pistons. As you can see, there are the nos 959 on the piston crown. I assumed, ( having studied all the "piston" type threads in the forum), that this gave the piston a diameter of 74.959. The cylinders are marked at .010 meaning a diameter of 75.010 giving a clearance when new of .051. The bike has 20k on the clock and from the look of the internals, this is her first major work. I also assumed that the pistons were standard and that I would be able to simply replace the rings with a standard size set and whack it back together.
Bought a set of vernier callipers, (Chinese and not the sort of tool you would use to measure your aorta), and measured the piston an inch up the skirt and the diameter of the cylinder. The figures were 74.93 and 75.10 respectively so I figured the piston had worn by 0.029 and the cylinder by 0.09 increasing the original gap by .119mm or .0046 inches. Even allowing for the inaccuracies of cheap instruments from Chinese sweatshops, I still felt that this was acceptable for replacement with standard rings.
I am now starting to have my doubts.
So.... I did 5 Twins piston in bore wear test and much to my disgust, I can stick a .009 feeler gauge in between the piston and the cylinder wall. You can see the gap in picture 2 and the feeler gauge rising like the banner of my dismay in picture 3.
It was then that I noticed the little 3 under the arrow on the piston crown. Is this an indication of a 3rd oversize piston? Would have thought that would have been signified by a 75 in place of the 959 on the crown. I find this somewhat disappointing as my machine shop fellow said the cylinders and pistons were in relatively good shape.
Am I reading this all wrong? Are my pistons and cylinders worn beyond salvation and do I need to rebore the lot and buy new oversize everything? Dare I fit standard or 1st oversize rings without going to the expense of new pistons? Should I have kept my Ducati and spent my old age wrestling with its electrics?
I realise that this is a relatively redundant topic but it has got me by the balls and I am not sure which way to jump.
Any opinions would be greatly appreciated.
I am in the middle of a rebuild. Took the engine to pieces and delivered the head and jugs to a machine shop where they honed the cylinders. Bloke told me that they had taken .0036 out of the original spec and that I would need to buy rings to suit.
The first picture below shows the top of one of my original pistons. As you can see, there are the nos 959 on the piston crown. I assumed, ( having studied all the "piston" type threads in the forum), that this gave the piston a diameter of 74.959. The cylinders are marked at .010 meaning a diameter of 75.010 giving a clearance when new of .051. The bike has 20k on the clock and from the look of the internals, this is her first major work. I also assumed that the pistons were standard and that I would be able to simply replace the rings with a standard size set and whack it back together.
Bought a set of vernier callipers, (Chinese and not the sort of tool you would use to measure your aorta), and measured the piston an inch up the skirt and the diameter of the cylinder. The figures were 74.93 and 75.10 respectively so I figured the piston had worn by 0.029 and the cylinder by 0.09 increasing the original gap by .119mm or .0046 inches. Even allowing for the inaccuracies of cheap instruments from Chinese sweatshops, I still felt that this was acceptable for replacement with standard rings.
I am now starting to have my doubts.
So.... I did 5 Twins piston in bore wear test and much to my disgust, I can stick a .009 feeler gauge in between the piston and the cylinder wall. You can see the gap in picture 2 and the feeler gauge rising like the banner of my dismay in picture 3.
It was then that I noticed the little 3 under the arrow on the piston crown. Is this an indication of a 3rd oversize piston? Would have thought that would have been signified by a 75 in place of the 959 on the crown. I find this somewhat disappointing as my machine shop fellow said the cylinders and pistons were in relatively good shape.
Am I reading this all wrong? Are my pistons and cylinders worn beyond salvation and do I need to rebore the lot and buy new oversize everything? Dare I fit standard or 1st oversize rings without going to the expense of new pistons? Should I have kept my Ducati and spent my old age wrestling with its electrics?
I realise that this is a relatively redundant topic but it has got me by the balls and I am not sure which way to jump.
Any opinions would be greatly appreciated.
