49cu 3 cyl bore size

[jim_in_day]

Well, i am staring at my disassmebled block and wondering if i am even close to understanding what I see. The bore is supposed to be 3". When I measure it with the Calipers, its more like 2.990. I think it might just be my calipers. If I get it bored for a .030 over piston, will that make the bore size 3.030?
Just asking because the machinist is going to ask me (yes he does 2 cycle outboards and has the appropriate tooling).

 

[mcallan]

Re: 49cu 3 cyl bore size

If you let me know the exact year, I will look in the service manual tomorrow and email you if you like. Mike@thompsonsmarina.com

 

[Dhadley]

Re: 49cu 3 cyl bore size

The standard bore size is 3.000. You can get a .020 or a .030 or .040 oversize piston.

If the machine shop asks you what the standard bore is, find another shop. Period.

 

[jim_in_day]

Re: 49cu 3 cyl bore size

DHadley, thanks, I thought that was the case, but after reading all the posts on pistons and replacement, I got a little confused. I think I confused bore and piston diameters, a .020 oversize piston is not 3.020 inches, the bore is and the piston is sized to correctly fit that hole(at least that is what I finally think is the correct answer). And the machine shop doesn't know the standard bore because I haven't actually taken the block to them yet, nor even given them any info about it. So I guess i cant condemn them about their lack of knowledge if I haven't told them enough.

 

[Dhadley]

Re: 49cu 3 cyl bore size

Yes, you are correct. The bore size it what we go by. As the fuel changes the engineers may change the shape and or actual size of the piston. Those potiental changes could be too hard to keep up with so we just stick to a given bore size and go from there.

On your motor we'd look for a finished bore size of 3.0205 to 3.021 for .020 over or 3.0305 to 3.031 for .030 over. With todays fuel that'll be just fine.

 

[jim_in_day]

Re: 49cu 3 cyl bore size

Thanks DHadley, that was just what I was looking for. How much wear on the piston skirts is acceptable? The reason I ask, is that I think I may be able to just hone the bottom 2 cyl. and re-ring if they are still in tolerance. I also will check for taper in the block, and if necessary bore the bottom 2 if they are out of spec, but obviously if I can get away with not buying all 3 pistons, my budget will appreciate it a lot.

 

[Dhadley]

Re: 49cu 3 cyl bore size

Just measure the cylinders. I'd almost bet that after they're honed they'll be right at max spec if not over. Lets start there.

 

[jim_in_day]

Re: 49cu 3 cyl bore size

thanks again, I will measure the bores and check, I assume that given what the oversize tolerances are that 3.0005 to 3.001 are the tolerances. Now all I have to do is find the cyl. mike in the shop.:% Oh well, I really think I know where it is, right in the tool box where it belongs.

 

[jim_in_day]

Re: 49cu 3 cyl bore size

Well, that was worthless. I will have to bring a real mike from home, the shop stuff stinks.