gt150 question

[jbower]

I just got a gt150 block back from machine shop. we had to replace 3 sleeves and bore the other 3. anyways they supplied marine power pro v pistons. I got the block on the stand yesterday and started checking ring gaps and they are really big. I put rings in 2 of the std new sleeved cylinders and im getting .036 in ring gap. I measured bore and am getting 3.507. I called pro marine and they told me that the gap is awfully big but to throw it together and run it. Now im no pro but I don't feel comfortable running a customers boat like this. I stuck a std ring out of my gt150 that has who knows how many hours on it and ring gap was .026...… WHAT DO I DO?? lol

[ChrisCarsonMarine]

You can throw it together and run it...in a few hours it will collapse the skirts and blow up...or save yourself the trouble and have those holes bored,and trade the pistons for the correct ones.Better check the size of the bored cylinders too...sounds like the machine shop added the recommended piston to wall clearance to the standard bore,hence the 3.507.The clearance is always built into the piston on production pistons,some custom pistons require you to clearance to taste,not these.One or two thousandths over would be ok,but 7 is way too much.Whatever the piston size on the box is the correct bore size,Chris

[jbower]

even at that it doesnt make up for the ring gap. stbd side std cylinder ring gap .045 next std .044 next .030 over .038
port side .040 over .034 gap next std .034 gap next .030 over .036 gap what gives

[FMP]

11.01756544 -10.99557429 = 0.02199" difference in circumference or gap for 0.007" bore increase

[jbower]

thank you i was just thinking about this !!!

[FMP]

Measure your next set of pistons, it won't take much to get the clearance. Can you get bigger than +.040 ?

[ChrisCarsonMarine]

I would be more concerned with piston clearance than ring gap...although they kinda go together.General rule of thumb on a stock water cooled 2 stroke is a minimum of 004-006 per inch of bore,so 016 to 021 would be optimal...Looks like you were alerted to the oversized bores by the oversized ring gaps... thats a good thing.Please accurately measure the bores,all of them,and report...realize the clearance is much more important than ring gap,Chris

[billybob]

Put it together & run the hell out of it, you will be fine. the older crossflow GT motors had domed pistns that retain more heat. I prefer bigger ring gaps on those motors.

[FMP]

Will it sound like a bag of hammers until hot?

[FORBESAUTO]

Check piston to cylinder wall clearance, if in spec, let her rip. If loose, fix it, you don’t want to break a skirt off and trash it or it not last long at all. I worry more about ring gaps being too tight and taking top of piston off than too loose as long as clearances are right. On going up to next size piston, you don’t want to be removing more than a few thousandths with a hone and need at least more than 5 thousandths to bore, so keep that in mind if ya need to get any oversized pistons.

[jbower]

I left the shop for the day and will get the bore gauge out monday and measure them all. My biggest concern is i had them do this cross flow and a intruder for me and ring gap on inturder is large as well. And yes i have another cross flow block with them and was getting ready to take a merc block to them.. This one was rebuilt by some one less than 3 years ago and here it is needing 3 sleeves and rebuilt again so im afraid the last guy just slapped it together and here we are

[FMP]

If these are stock motors keep it true to the box measurement, but double check the measurements on the pistons.

[ChrisCarsonMarine]

Put it together & run the hell out of it, you will be fine. the older crossflow GT motors had domed pistns that retain more heat. I prefer bigger ring gaps on those motors.

You're ok with an extra 007 clearance?,thats going to be 015-017 piston to wall clearance...The factory service manuel(what do they know) states that 003 is the maximum allowable oversize,any more should be bored to next oversize...

[jbower]

Ok so I went threw with the bore gauge. not sure why i got a 3.507 but here is what i have.. stbd 3.503,3.501,3.530
port 3.540,3.500,3.530 so im guessing these rings are just junk. What do you think I should do? I understand big gap isnt going to hurt anything but i'd prefer to do it the right way

[FMP]

You're ok with an extra 007 clearance?,thats going to be 015-017 piston to wall clearance...The factory service manuel(what do they know) states that 003 is the maximum allowable oversize,any more should be bored to next oversize...

Do this, measure the pistons to the correct bores. Those pistons and rings all new?

Warm the rings up above room temperature, sorry just a little cold weather humour