New Blaster, need jetting help

[Tbrock77]

Just got back in from the garage. Swapped reed cage, didn't change compression, still 100psi.

Float was fine.

I decided to pull the head to double check the piston size so while I was in there I also checked the piston clearance. I know the way I did it isn't the proper way to check it but I'll throw in a link to a video of what I did so you guys can tell me what you think. I was able to get a .008 all the way around the piston, but couldn't get the .009 all the way around. If this crude method has some merit then that's obviously way too much.

 

[Awk08]

you're can check the clearence just like you did it....except from the bottom, which requires the clylinder and piston off the bottom end

 

[Tbrock77]

you're supposed to check the clearence just like you did it....except from the bottom, which requires the clylinder and piston off the bottom end

darn... so those top measurements don't mean anything? I can take it apart and do it again from the bottom but I'd like to get some opinions on where the compression is going before I take the next step. I had a stock blaster in my garage before and it has 130 psi compression so it's not my elevation. There were no grooves in the cylinder wall at all, it looks really fresh, I can still faintly see the hash marks.

 

[Awk08]

could just need a quick hone and new rings if the clearence checks out ?

 

[speedyslyder]

measure the cylinder with a digital caliper...cheapest way at least?
measure piston.
the top of piston is tighter then the bottom/it is like oval piston/not straight up n down
measure piston in middle or as showed in video.
the cylinder head and gasket have alot to do with compression as well/warped head or leaking head gasket will show same results...make sure head is not warped

im not sure about your feeler gauge method of testing/all i could say about that is measure the ring end gap with ring inserted on cylinder/without piston

 

[Tbrock77]

could just need a quick hone and new rings if the clearence checks out ?

I'll take it apart and check the clearance tomorrow.

When I do that I want the piston in there with the rings still on it and insert the feeler gauge from the bottom up until I can't anymore?

On a side note, just kinda thinking ahead. If I'm still getting .009" of clearance how unwise would it be to just hone it another .004" to go to a 66.50mm piston? I know some machine shops will hone out the last .003" to really smooth everything out so I can't imagine another thousandth could be bad? I am a mechanical engineering student so I do have access to the tools to measure the bore and check for roundness.

 

[Awk08]

If I'm still getting .009" of clearance how unwise would it be to just hone it another .004" to go to a 66.50mm piston

you still need the .003-.004 clearence beyond the 66.5 piston, depending if the piston has the clearence built in or not. some do, some don't.
if it's out of clearence spec, just get the next size piston and let the shop decide how to do it, bore, hone, or both

 

[Tbrock77]

you still need the .003-.004 clearence beyond the 66.5 piston, depending if the piston has the clearence built in or not. some do, some don't.
if it's out of clearence spec, just get the next size piston and let the shop decide how to do it, bore, hone, or both

Well if it's at .009" of clearance that's .2286mm so that'd put the bore roughly around 66.48mm. I could order the next size piston, take measurements and hone the cylinder out to that size with the proper clearance (the .004" was referring to the clearance for the 66.50mm piston) which I would get from the piston manufacture (After checking roundness throughout cylinder) It's my girlfriends quad and she's paying for everything to be done so I don't want to spend money unless I have to, not trying to be cheap but if I have the knowledge and tools to do the job I don't see why not? I also have 2 teachers that can assist me so the job gets done right.

 

[speedyslyder]

Just got back in from the garage. Swapped reed cage, didn't change compression, still 100psi

i would not be intrested if i just got it done with only a 100psi. i have seen totally worn top ends with wrist pin's worn so bad that they would not comeout....With perfect compression despite the severely negleted top end
waste of time/money

 

[Tbrock77]

Uhh, what?

I was told it was done about a year ago, and from the looks it was. The head could be warped, I'm going to bring it to class tomorrow and check it's flatness, I have a spare which I'm also going to bring to check to.

 

[speedyslyder]

ok
only other advice is leak test it to ensure it will last and air tight
a airleak will destroy it with in hours
http://www.blasterforum.com/threads/about-air-leaks-save-your-engine.55537/#post-763164

 

[Tbrock77]

ok
only other advice is leak test it to ensure it will last and air tight
a airleak will destroy it with in hours
http://www.blasterforum.com/threads/about-air-leaks-save-your-engine.55537/#post-763164

Definitely! I'm either going to order a leakdown tester or build one. If I hadn't needed to lean it out so much I would have started with an air leak.

 

[Tbrock77]

I think I found the problem.

I measured the ring end gap, which I figured out needed to be .010" for this size piston (2.608" x .004" = .010432) I got that formula straight off the wiseco website. So I put the top ring in, squares it with the piston and WOW was all I could otter. Just for sh*ts I pulled out the .035" gauge and there was enough room for 2-3 of them! Tried the bottom ring and ended up with the same answer. The rings haven't been grinded at all, they still have the point on the ends. I checked piston clearance next and was getting .006" on the skirt side and .004" on the perpendicular side, which from what I read is within reason.

I'm guessing I need new rings? Haha

Sorry about the background noise, I was in our solar panel room control room because it's always really warm in there.

 

[Tbrock77]

Opinions anyone?

I showed my dad the video, he's been racing air cooled 2 strokes go karts for the last 15 years, one of them being the KT100 from yamaha. He said it looks like the cylinder is really out of round and the rings have either been really messed with or aren't the right rings.

Just looking to get some opinions from you guys that know these motors and quads before I take the next step.

 

[tbrooks]

That ring gap looks huge, you need to use a bore gauge to check the cylinder

 

[Tbrock77]

I'm going to have it bored to the next size. It's out of round and there is some marks in it. And we'll have the peace of mind of knowing when it was done