So I did a comp test today

[ssv1761982]

Thanks for the extra explanations Roy & Gary.

 

[XXXR2001]

BUT...........a leak down test reveled otherwise.

"don't know why this thing still made the power it did.

I did a cylinder leak down on the engine tonight after slapping the heads back on."

#2. 32% #1. 18%
#4. 23% #3. 18%
#6. 28% #5. 20%

"Seems a little high!"

" I put a flywheel holder that I made to clamp onto the flywheel and rest against the starter, keeps it from rotating. Put #2 piston down about 1/4" above the exhaust port and recorded 70%. Moved it again about 1/2" above and had 85% leakage, could have been where the exhaust relief hole was in the bore. That is if the sleeves have that hole.
#6 was 50% leakage 1/4" above."

As you can see from this, compression can seem good but this engine was hurting from scored cylinder walls, it ran well enough though.

It ran well because those leakdown #s are wrong. You have to hold the piston at tdc to get an accurate leakdown reading.

 

[xb03]

I'm buyin a leak down tester, will post #'s later this week.
Thanks

 

[2003225X]

I have been told the very best way to get an accurate leakdown is to test it through the entire stroke of the piston. Is that not correct??

Another good thing to remember is you must rotate the motor the correct way for each side of the motor or your leakdown numbers will not be correct.

 

[XXXR2001]

I'm buyin a leak down tester, will post #'s later this week.
Thanks

Now that you've been convinced to buy this tool, make sure you use it correctly or you're wasting your time. It's not easy to do it right and unless you have some way to keep the flywheel from moving, it's a 2 man job.

In addition to the leakdown tool, you'll need a breaker bar with a deep socket to fit the flywheel nut. You'll also need a tool to measure top dead center.
The procedure is to bring the piston being checked to tdc and keep it there while compressed air (probably at 100psi) is beeing pumped in through the sparkplug hole. You need someone to hold it in place and it'll take a lot of effort if the piston moves from the air pushing on it. I've tried to do it myself and trust me it is dangerous! Some times the piston is centered perfectly and doesn't move but other times it gets pushed by the air.

Seriously, I wouldn't waste your money on the tool. It's too much of a pain in the *** to use it correctly. jmo

 

[2003225X]

Now that you've been convinced to buy this tool, make sure you use it correctly or you're wasting your time. It's not easy to do it right and unless you have some way to keep the flywheel from moving, it's a 2 man job.

In addition to the leakdown tool, you'll need a breaker bar with a deep socket to fit the flywheel nut. You'll also need a tool to measure top dead center.
The procedure is to bring the piston being checked to tdc and keep it there while compressed air (probably at 100psi) is beeing pumped in through the sparkplug hole. You need someone to hold it in place and it'll take a lot of effort if the piston moves from the air pushing on it. I've tried to do it myself and trust me it is dangerous! Some times the piston is centered perfectly and doesn't move but other times it gets pushed by the air.

Seriously, I wouldn't waste your money on the tool. It's too much of a pain in the *** to use it correctly. jmo

I agree with that 100%. If tough are checking it at tdc someone will have to hold the flywheel. The motor must be turned the correct way and everything must be PERFECT for you to get an accurate reading.

 

[XXXR2001]

I have been told the very best way to get an accurate leakdown is to test it through the entire stroke of the piston. Is that not correct??

Another good thing to remember is you must rotate the motor the correct way for each side of the motor or your leakdown numbers will not be correct.

You might rotate the piston on a 4 stroke, I have no idea about that but why would you on a 2 stroke? Once you lower the piston below the top of the exhaust port air will leak out the port. That tells you nothing.

 

[procomp]

I use a TDC tool from Jay Smith and more often then not I get it bang on and you don't even have to hold the flywheel.

 

[K-DAWG XB 2003]

I agree. When I do mine I use a tdc gauge. Get it to top dead center and it wont move if its at tdc. Never had a problem doing it this way.

 

[patches]

I get mine to TDC with a dial indicator and charge it with air. I DO NOT attempt to hold it with anything. Thats a good way to lose teeth. If it moves I just reset and do it again. After doing a few with the dial indicator you get a good feel for exact TDC and it won't move. There's enough dwell in a 2.5 that its not too hard

 

[SLOmofo]

It ran well because those leakdown #s are wrong. You have to hold the piston at tdc to get an accurate leakdown reading.

Please do me the favor of reading it again.



It's a comparison, first is TDC then piston down in the bore.

I already knew it was hurt because I had the heads off and put them back on to do the leak down.

I might say the reason I did the testing in the first place was because of the Pyro readings I recorded and then played back after I got to the ramp, still running as before. There is a probe in each cylinders exhaust port.
Two, 3 screen RacPak III's I have it written down at home 2 cylinders were above 1600 degrees. It was a little rich still.

 

[h2oskiier30]

PI have it written down at home 2 cylinders were above 1600 degrees. It was a little rich still.

:shock: :shock: :shock:

 

[XXXR2001]

I get mine to TDC with a dial indicator and charge it with air. I DO NOT attempt to hold it with anything. Thats a good way to lose teeth. If it moves I just reset and do it again. After doing a few with the dial indicator you get a good feel for exact TDC and it won't move. There's enough dwell in a 2.5 that its not too hard

Good advice! Will take that advice myself. My motor seems to be about 50/50 chance of the piston staying in place but I just need to exercise a little more patience I suppose.

 

[xb03fs]

Harry I have a jsre TDC gauge still in box you can borrow any time bought it a while back when I was thinking if taking the timing modules off never took them off

 

[Bobalouie]

This is the leakdown tester Jay Smith likes:http://www.freewebs.com/bttwracing/index.htm
Looks very well (American) made but like most good tools you pay for it.
This OTC is a real value for the money.
http://www.amazon.com/Otc-5609-Cylinder-Leakage-Tester/dp/B000R5G0F2
For guys like myself that will only use it a few times per year the OTC would be fine. Good luck.

I have the OTC model and like it.

 

[Bobalouie]

Now that you've been convinced to buy this tool, make sure you use it correctly or you're wasting your time. It's not easy to do it right and unless you have some way to keep the flywheel from moving, it's a 2 man job.

In addition to the leakdown tool, you'll need a breaker bar with a deep socket to fit the flywheel nut. You'll also need a tool to measure top dead center.
The procedure is to bring the piston being checked to tdc and keep it there while compressed air (probably at 100psi) is beeing pumped in through the sparkplug hole. You need someone to hold it in place and it'll take a lot of effort if the piston moves from the air pushing on it. I've tried to do it myself and trust me it is dangerous! Some times the piston is centered perfectly and doesn't move but other times it gets pushed by the air.

Seriously, I wouldn't waste your money on the tool. It's too much of a pain in the *** to use it correctly. jmo

I have never had a problem checking it by myself. If you have an accurate TDC gauge, and set it dead nutz at TDC, the piston wont move on you when you pump the air to it. Everything will be in alignment. If you are a couple of thousanths off though, you will hear the piston whump back to BDC and you have to start again. Just take your wrench off the flywheel before you put the air to it, so you keep your teeth!

 

[K-DAWG XB 2003]

Whn I sold my 260 a month ago. The guy who bought it wanted to see me do a leak down. I got my tdc gauge. Brought the piston to top dead center and hooked up my leakdown tester and turned it to 100 on the first gauge the second gauge goes to 98 psi. Told him that was 2% leak down. Done all the cylinders they were all the same. After I was finished. He told me he had never seen a leak down tester like that. He had never seen it done like that and he wasnt sure he believed it. Told me he buddy had a snap on test that you put a wrench on the crank shaft put the air to it and pulled the piston up the cylinder to tdc to test the leak down. Told him I had never heard of that. Any how. He pulled the motor apart after he got it home he informed me that the rings were shot. I personelly dont believe him. You could see the rings thru the exhaust on the bottom of the motor. They looked fine to me. He also told me the nic coating was as new. Dont make much sense to me to have shot rings and cylinder wlls that look like new. He also never returned my lifting ring that I forgot to take off that he told me on the phone he would mail out. Wish I would have sold it to someone else.

 

[xb03]

Whn I sold my 260 a month ago. The guy who bought it wanted to see me do a leak down. I got my tdc gauge. Brought the piston to top dead center and hooked up my leakdown tester and turned it to 100 on the first gauge the second gauge goes to 98 psi. Told him that was 2% leak down. Done all the cylinders they were all the same. After I was finished. He told me he had never seen a leak down tester like that. He had never seen it done like that and he wasnt sure he believed it. Told me he buddy had a snap on test that you put a wrench on the crank shaft put the ait to it and pulled the piston up the cylinder to test the leak down. Told him I had never heard of that. Any how. He pulled the motor apart after he got it home he informed me that the ringsd were shot. I personelly dont beleive him. you could see the rings thru the exhaust on the bottom of the motor. The looked fine to me. He also told me the nic coating was as new. He also never returned my lifting ring that I forgot to take off that he told me on the ohione he would mail out. Wish I would have sold it to someone else.

Some people

 

[LakeAnna]

Lee checked mine I just noticed on my bill and he listed all cylinder 6-8%. I guess that means it's okay but not super? On a craftsman comp. gauge they all had around 125 with the short adapter whether that matters or not I don't know. I think Jay Smith posted something about using a long adapter to get a more true reading. Like I listed before my engine has 192 hours on it at this point. It is what it is...hope she will last for a while.

 

[Blob-head]

2005 280 97 GS

Bought my engine new spring 2005. did a comp test with my LISLE gauge
a few months later, all #'s 128 -138. Did the same test this past spring. all#'s 130-138. Same gauge same oil -Merc Hi Per Blend Same gas Chevron 91
same elevation 2000 feet. Boat still runs same mph to same rpm with
same props. Always thought I was leaving power on the table compared to
what I read here 150-160. I don't know, but boat runs the same after 7 years, engine never been apart.



Bob I guess my point is Don't fix what's not broke. Good Luck