ring end gap ?

I am rebuilding my 175 faststrike myself. This is my first time. I had it rebuilt in the spring by a local marina. The motor gave me problems and when I had taken it to another marina I then found out the motor was blown . I am using the omc manual for this motor and I used the charts and the procedures listed to check the ring end gaps and found them out of tolerence. My cylinder bore dimensions are at their upper ends from 3.598 to 3.600 and when I put the rings inside the bore on at least 2 of the cylinders I found the end gaps at about .0400 instead of the .0110 to .0230 that the chart stated they should be. I am asking how critical these dimensions are and could this have caused the motor failure that I have experienced. Should I go to oversized rings? I am thinking in that direction. The power pack was found to be going bad and all cylinders were not always firing. The piston was scrubbing the bore wall but had not seized up the motor. the engine would still crank and rev up to it's full rpm but had lost compression on two cylinders. Any help on the ring gaps would be appreciated.

Re: ring end gap ?

.012 to .020 are good, stay towards the tight side.

Clean to piston tops and look carefully for any #'s, like 030 indicating an overbored cyl/piston which will require matching o/s rings.

Re: ring end gap ?

If you dont have a bore guage and know how to measure the bores you will be groping in the dark. A shop that bores outboads may be inclined to check the bores for you. Compare the measurements with the specs and that will tell you what you have and address accordingly.

Re: ring end gap ?

I am checking the bores at the locations specified by the manual and I am using a telescoping snap mic from starrett and a OD mic. I am wondering if my rings are just worn. I am thinking that when I had my motor rebuilt this spring that the guy did shabby work and he may have put worn rings back in my motor. Not sure. Seems like my ring gap is too big out of print by as much as .0150 and I want to know if I went with .0100 or .0200 over rings would this tighten my ring gap down into tolerence and does it really matter that much. Thanks.

Re: ring end gap ?

I dont know what your manual says but you should check the ring gap in an unworn part of the bore and you must put them in squarely to check.

If the gap is too large then the compression will suffer but if it is less than the minimum figure given they may close up when hot and possibly seize.

If the engine has been rebored then the appropriate oversize pistons should be fitted and the correct rings as well. If the engine has not been rebored you'd expect the standard rings (and pistons)to be fitted.

Re: ring end gap ?

There is no such thing as an over size ring. In other words, you can't put over size rings on a standard piston. When you go oversize on an engine, you use both over size pistons, and rings. I have always found the ring gap to be quite generous on these engines, and not match the spec's in the manual. What you don't want is to small of a ring gap that could close shut on it's self when hot. That will cause a problem.

Re: ring end gap ?

2 stroke rings are not square on the ends like a four stroke, often even minimal minimal end gap filing done to the 2 stroke ring and the ring will NOT fit correctly once at operating temp, colliding with the ring locating pin, then the ring will distort, destroying itself, the cylinder wall, AND the piston.

Over-sized rings on a 2 stroke piston is a recipe for expensive trouble.

Part manufacturers quality control is far better than they used to be many years ago. I ALWAYS check ends gaps, got to be sure, but haven't had to make any adjustments in a LONG time, unless I screwed up and ordered the wrong rings, and even then I simply exchange them for the correct rings.

Re: ring end gap ?

You'll also want to check the updated bore spec. 3.598 is way too tight. But it's typical to have measurements that aren't quite right doing it the way you are. Just too much lost in the translation so to speak.

Don't worry about the old rings, you're not going to use them anyway. We do the same as mentioned above - just check the end gap to make sure we have the right ones.

Re: ring end gap ?

Thanks everyone . Your info helped allot. I am going to ask another question under another title about something else I found wrong.