Engine Pressure Test Opinions

[///M5]

I rebuilt my friends 760 motor, and I am pressure testing it before install.

I pressurize the motor to 10 psi, and it drops an average of .7 - 1psi over 10mins.

After 20mins it drops about 2psi, and in 30mins it will drop a total of close to 3psi.

Am I good, or should I be looking for a leak?

Thanks

 

[Dartman]

6-8 psi test is fine
sounds ok to me
if you lost 2 psi in a min thats enough to find the leak

 

[Proformance1]

the supposed rule is 10% over 10 mins. I pressurize to 5 psi with no reeds installed.

 

[///M5]

6-8 psi test is fine
sounds ok to me
if you lost 2 psi in a min thats enough to find the leak

Ok, it's nowhere close to 1 or 2 psi a min, and not even 2psi in 10mins so I'm good.

Thanks for the info.

 

[///M5]

the supposed rule is 10% over 10 mins. I pressurize to 5 psi with no reeds installed.

Is the 10% loss in 10mins acceptable or not?

 

[Proformance1]

correct, there is also a tech section where this should be covered in more detail. you can also spray soapy water on the motor and find the leak check you front and rear seals as well as intake bolts

 

[///M5]

correct, there is also a tech section where this should be covered in more detail. you can also spray soapy water on the motor and find the leak check you front and rear seals as well as intake bolts

Thanks, I was looking for that all night, and only found some vague stuff.

When you say correct, is the 10% loss over 10mins acceptable or not?

 

[///M5]

I found the leak...

It seems that the spark plug seat has some corrosion letting the pressure escape.
Any ideas of how I could repair it to stop the leak?

Thanks

 

[///M5]

Fixed it!

I put the piston to tdc and stuffed the hole with a paper towel to catch any debris. Then I sanded the plug seat with 150grit paper by hand until the small pits were removed.

The motor now holds 8psi for 30mins with no drop in pressure.

Here are pics of my setup and repaired plug seat.

 

[Pro-pulsion]

Nice job fella, now when you put that flywheel cover back on, do yourself a favor and add about 3 cap fulls of atf into the flywheel cover. It will help keep the bendix lubricated and in good shape as well as keep the rust and condensation on the flywheel under control.

 

[///M5]

Nice job fella, now when you put that flywheel cover back on, do yourself a favor and add about 3 cap fulls of atf into the flywheel cover. It will help keep the bendix lubricated and in good shape as well as keep the rust and condensation on the flywheel under control.

Will the ATF interfere with the electrical?

 

[Pro-pulsion]

Nope, I have been doing that for years. I think it helps preserve everything inside including the crank seal. It not only lubes the moving parts but also prevents condensation and like all lubricants it will collect and contain dirt and debris rather than let it fly around inside. The next time you remove the cover you will have to wipe out the bottom area of it because there will be black or brown sediment from the rust and any other residues in there. But the important parts will be clean. Plus with the rust being controlled, the pulse coil won't collect iron filings the way dry ones do. Eventually they collect up enough and reduce your clearance gap interfering with pulse timing. I have seen it happen on lawnmowers so many times. Clean the filings out and the thing runs fine, that was the only problem lol. I also found my flywheel never had a hard time being removed with the puller after I started using the ATF. Before the ATF the flywheel would seize onto the taper and make a fuss to remove it.

 

[///M5]

This motor originally seized the PTO piston. When I tore it down the flywheel and stator were a rusted mess. It looks like water or condensation did get in there at some point, and I had to sand the flywheel to remove some of the heavier stuff. Everything is cleaned up now, so I will try your ATF trick.

Thanks

 

[Pro-pulsion]

No probs mang. For how little you need it saves a ton of effort later

 

[Proformance1]

fyi, 10% loss over ten mins is okay. Not what i would do but decent enough for most

 

[///M5]

Just an update. Motor ran perfect for 1 day then the stator went out.

I don't know if it's pure coincidence, but I don't think I will put ATF in the stator cover again. (Maybe the 64x electronics don't like it?)

Picked up a used stator and we are back in business!

 

[Pro-pulsion]

Wow, I'm sorry to hear that man. Is the entire stator or the trigger coil? Because more often than it's the usually only the one replaceable coil.

 

[///M5]

Don't worry about it. It could just be coincidence, but I'm not willing to find out lol.

Once I figured out it was the stator, I just picked up a used one off the Bay (cheaper than buying any single part).

 

[Pro-pulsion]

Agreed, I certainly hope it was coincidental lol, I have been using atf in all my skis stator area since my first Kawi JS300. I remember asking our local Kawi dealer when I was 16 why there was a what I thought to be an oil check plug above the flywheel cover. He said it was a timing mark inspection hole. I asked if there was supposed to be fluid in there because some came out when I had to rebuild it. He said no but we do that all the time, just a cap full is all you need to help prevent rusting and save seal life.

 

[///M5]

Agreed, I certainly hope it was coincidental lol, I have been using atf in all my skis stator area since my first Kawi JS300. I remember asking our local Kawi dealer when I was 16 why there was a what I thought to be an oil check plug above the flywheel cover. He said it was a timing mark inspection hole. I asked if there was supposed to be fluid in there because some came out when I had to rebuild it. He said no but we do that all the time, just a cap full is all you need to help prevent rusting and save seal life.

If I try it again, it will be in my own not someone else's boat lol