ring gap 77' Johnson 140

[miller21]

I'm rebuilding powerhead on 77 Johnson 140 with standard pistons. I'm replacing with Wiseco pistons and rings. Manual I have says ".07-.170 ring gap. Am I reading this correctly that this is 70 (seventy) thousandths up to 170 thousandths<br />or is my manual got the decimal in the wrong spot. I've been told it should be 7 (seven) thousandths. others have said that with the Wiseco pistons I should take the rings out of the box and put them in, period. Cylinders are in perfect condition.<br />Any ideas before I grind these rings.

 

[Dhadley]

Re: ring gap 77' Johnson 140

In the "good ol days" the gap was .007" to .017". With todays ring materials and fuel they may be more. Do not, repeat, do not grind those rings.<br /><br />Which series pistons did you get? Whats the complete part number of the piston?

 

[miller21]

Re: ring gap 77' Johnson 140

Not sure which series. They came from Benrock in Tulsa OK. 3.500" bore x 2.588" stroke. Piston displacement is 99.6. Out of the box and put in the cylinder about 2" deep the gap is already .010. If the specs were suppose to be between .007 and .017, I'm fine. But the manual I have says .07-.170. Its a Seloc book. In fact it also has it as 1.8mm- 4.3mm. to get a gap that big the tabs that go around the pin are going to be gone. we also noticed that out of the box we don't have the same gap on all 4 cylinders. Is this going to be a problem.<br /><br />Thanks for your help

 

[DJ]

Re: ring gap 77' Johnson 140

I have also always heard/thought. .007" to .017.<br /><br />Differences in cylinders should not matter, as long as they are within spec.

 

[mrtool2u]

Re: ring gap 77' Johnson 140

I cannot believe it would be .70,,some times it is in metric,and you need to break it down to american,at least it is for snowmobiles.

 

[Dhadley]

Re: ring gap 77' Johnson 140

Whatever manual your reading is not right. We dont even use the old .007 to .017 spec anymore.<br /><br />Whats the part number on the piston box?

 

[miller21]

Re: ring gap 77' Johnson 140

already threw boxes away, sorry. Was just informed that on two pistons the rings were already gapped at .070 before I sought advice. Now my question is do I gap the other two the same or do I leave them at .010 or .011 as they are out of the box, or is this just not going to work and I need to start over. Piston 1&2 are gapped at .070 and pistons 3&4 would be .010 & .011 respectively. Is this a better situation than having all 4 at .070. How much compression am I going to lose and what other problems could I have.

 

[Dhadley]

Re: ring gap 77' Johnson 140

What is the piston part number??? <br /><br />Its stamped on the dome.

 

[Dhadley]

Re: ring gap 77' Johnson 140

What ever happened?