Problem lapping contra poston to cylinder?
06-14-2015, 05:30 AM
#1
Thread Starter
Problem lapping contra poston to cylinder?
Hello All:
I have been attempting to lap a contra piston to a cylinder with little success. I spent a few hours yesterday pushing the contra piston into the cylinder while both were coated with an abrasive. I seemed to make no progress.
I started with Dupont red polishing compound but gave up due to making little progress. I then switched to an 800 grit abrasive that was supposed to be the answer. After many trips of the cp through the cylinder, I again gave up due to no progress.
My method is as follows:
Coat the inside of the cylinder with paste of oil and abrasive.
Coat the cp with a coating of the abrasive paste.
Push the cp into and out of the cylinder using a large vise and wooden dowels.
Stop and clean the parts with hot water, soap, toothbrush, spray with WD 40, spray with carb cleaner, lightly oil and check for fit.
I repeated this routine many times but I have not seen any change in the fit of these parts.
Is it time to switch to a piece of fine wet and dry paper wound on a dowel to get things started to a point where I can begin to lap the parts together. Once he cp goes past the top of the ports, it becomes very difficult to move! I takes a considerable force to move the cp!
Oh yes, the piston is also tight in the cylinder but that is the next dilemma.
Is there anybody to whom I may send this engine to have the parts fitted?
Suggestions?
Be well my friends,
Fanchi
I have been attempting to lap a contra piston to a cylinder with little success. I spent a few hours yesterday pushing the contra piston into the cylinder while both were coated with an abrasive. I seemed to make no progress.
I started with Dupont red polishing compound but gave up due to making little progress. I then switched to an 800 grit abrasive that was supposed to be the answer. After many trips of the cp through the cylinder, I again gave up due to no progress.
My method is as follows:
Coat the inside of the cylinder with paste of oil and abrasive.
Coat the cp with a coating of the abrasive paste.
Push the cp into and out of the cylinder using a large vise and wooden dowels.
Stop and clean the parts with hot water, soap, toothbrush, spray with WD 40, spray with carb cleaner, lightly oil and check for fit.
I repeated this routine many times but I have not seen any change in the fit of these parts.
Is it time to switch to a piece of fine wet and dry paper wound on a dowel to get things started to a point where I can begin to lap the parts together. Once he cp goes past the top of the ports, it becomes very difficult to move! I takes a considerable force to move the cp!
Oh yes, the piston is also tight in the cylinder but that is the next dilemma.
Is there anybody to whom I may send this engine to have the parts fitted?
Suggestions?
Be well my friends,
Fanchi
06-14-2015, 04:10 PM
#2
Thread Starter
UPDATE
I removed all traces of lapping compound from the cylinder and piston an pushed the cp in and out of the cylinder until I got a good fit. There was no scratching or scoring of the parts.
How and why this worked is beyond me! Do not question success!
Do not be bound by reality,
Franchi
I removed all traces of lapping compound from the cylinder and piston an pushed the cp in and out of the cylinder until I got a good fit. There was no scratching or scoring of the parts.
How and why this worked is beyond me! Do not question success!
Do not be bound by reality,
Franchi
06-15-2015, 10:53 AM
#3
Thread Starter
Great news:
I fired up the above engine and it started right up after I found the magic compression and needle vale setting. It restarts very easily and has great power! Sometimes one get lucky!
Have a great day,
Franchi
I fired up the above engine and it started right up after I found the magic compression and needle vale setting. It restarts very easily and has great power! Sometimes one get lucky!
Have a great day,
Franchi
