bore size???

[stairliftoheaven]

stripped my engine: evinrude 60hp BE60TLCO; gonna rebore due to mashed piston in one cylinder and i need to know what oversize pistons to buy. I don't think its been rebored before as the remaining good piston has no markings except for the the word 'top' stamped onto the casting. I've measured the good cylinder at 3.181"-3.184" across the top of the bore. So need to know original spcification for engine before ordering new pistons. Anyone have nominal bore diameters for this engine? Also how much clearance should there be between new pisotn and bore?<br /><br />thanks in advance!<br />chris

 

[Paul Moir]

Re: bore size???

You might want to double check your measurements. The standard bore is 3.187 for that engine.<br />As for the clearance, that should depend on what brand of piston you buy. Follow their recommendations.

 

[walleyehed]

Re: bore size???

Forget the piston to cylinder clearance, it'll get ya in trouble. Use standard bore, as Paul mentioned, and bore over according to that.<br />ONLY the piston manufacturer knows the expansion of their piston material, and it's not important to know the fit clearance.<br />If your std. bore size is 3.187, then 3.207 is the measurement you want for .020 over, etc.<br />EDIT: It would be a good idea to understand completely, where the measurements must be taken...there are 4 critical locations that must be measured to figure what actual wear is..

 

[Walker]

Re: bore size???

You need to take the block to the people who are going to bore it and have the bad cylinder checked to see what its going to take to clean it up. No use buying +.020 pistons if they have to bore it +.030

 

[Dhadley]

Re: bore size???

The standard bore is actually 3.1875". That extra half thousand becomes real important. Make sure that the machine shop you use is accustomed to boring outboards.

 

[Dhadley]

Re: bore size???

Do you know what caused the "mashed" piston?

 

[stairliftoheaven]

Re: bore size???

thanks for the replies guys; i took the measurements myself with a digital caliper so may not be too accurate. I think I'll take it to a marine engineer to establish how much to re-bore; the bad cylinder is in a bit of a state lol; piston got a hole in it as well! Dhadley, i bought the engine as a non runner so will rebuild as necessary. I think the previous owner never used to run it out of fuel prior to storage so i have an idea a carb got blocked and the engine leaned out on one cylinder. Could be wrong tho, will need to check that carefully when powerhead is reinstalled

 

[Dhadley]

Re: bore size???

What spark plugs were in it? Running a motor dry is a bad idea.

 

[walleyehed]

Re: bore size???

Walker, I used .020 as an example, not a recommendation, and DH, thanks for adding the 1/2 thou....I can only imagine that mess...I didn't actually look up the bore, just wanted to make it clear (as mud) that you use std bore as the guide and not the piston.<br />stairlift, you got Dhadley on the scene...best tech on this site (and many sites)..give him your info and he will have the answers.

 

[stairliftoheaven]

Re: bore size???

takin me block to the shop saturday to find out how much they need to bore out. spark plugs that were in the motor when I got it are NGK B7HS, also propped at 11 3/4 X 17 on a 16'6" glastron bowrider. <br />thanks for the help guys. By the way there's a little damage aroound the mouth of one of the transfer ports and a nick out of the side of the exhaust port about 1/8" long and 1/8" deep where i guess the broken ring got trapped. Is bad news?<br />thanks again<br />chris

 

[Dhadley]

Re: bore size???

I would not be surprised if its propped a bit much. That and the wrong plugs may have been enough to push it over the edge. <br /><br />I wouldnt worry too much about the nick in the side of the exhaust port. Just make sure the sleeve isnt cracked. Sometimes ya gotta look real real close. A tiny nick in a transfer might be OK.

 

[stairliftoheaven]

Re: bore size???

ok i'll take a closer look at the liner. <br /><br />many thanks

 

[Dhadley]

Re: bore size???

Just make sure you use Champion plugs when you get it back together.

 

[stairliftoheaven]

Re: bore size???

yeah sure but which ones please?

 

[Dhadley]

Re: bore size???

There are a couple that are recommended but I tend to like the cooler QL77JC4's. Whoever rebuilds your motor will have a recommendation and I would defer to that (his set up) as long as they are Champions.

 

[stairliftoheaven]

Re: bore size???

Took block to the machine shop this morning, He's gonna measure it all up on monday. I've told him nominal bore size should be 3.1875". Will find out what size pistons to buy next week. I also took the head to him weld and skim as the event which mashed the piston also made a bit of a mess of the head lol: Don't know if it's been skimmed already though. Anyone have an idea what the thickness of the head should be so I can pass info on to the machine shop. Thanks guys this is a great forum.<br />Off to Wiltshire to an open air concert now probably gonna pour with rain in keeping with the british summer! regards<br />chris