Pressure Testing Two Stroke Engines

[TX21]

fyi 10 psi will blow out your crank seals. Just learned that one. Thought It was 10 and didn't think twice before I pumped away....la la la la POW! Cold beer made me feel better. Have to replace them tomorrow so I can get my first ride of the season.

So I get it back together and the crank seal leaks along with the case where it meets the seal.

This is my 10+ two stroke jet ski build and I still got it wrong. Bottom line .....test.

[quadzilla]

65U

Here's a somewhat extreme version of pressure testing a two stroke motor..

This particular motor was proving difficult to track down the slow leak it had.
- was leaking about half a psi per minute (actually, it was almost 2psi every five minutes)

It's all good now of course..

[quadzilla]

push/pull=pressure-vacuum...

How does this apply to testing jet pumps?

Hey there.

I would imagine he actually means testing the fuel pumps with vacuum and pressure to ensure the diaphragms are intact.

.

[K447]

push/pull=pressure-vacuum...

How does this apply to testing jet pumps?

[dockwalker]

Amazing how hard it is to convince some folks that their crap is getting ready to explode.Got a couple around me.

[nmpeter]

push/pull=pressure-vacuum

most of the time when I have to tell a customer his engine is leaking, they never go for the repairs

got one in the shop now, kaw 1100..has a deadly case leak somewhere..start the engine and it will idle for a couple of seconds then go screaming to redline and dieseling so bad I have to stuff the carbs to shut it down.

even tried it with my known good carbs..gaskets all replaced..still screaming.

Told him it would be an hour labor to confirm the air leak issue and perhaps fix it if it's readily accessible, but he didn't want to spend more then a couple of hundred on the ski since he got it cheap at an auction.

Since that discussion I have not heard from him, nor have my calls been returned.

heading to the yard queen area in another week or two. That was the last time I ailed to listen to the voide in my head saying "send him away..send him away"

only downside for me was I cut my thumb pretty badly on a ziptie pullin the carbs off.

[K447]

good idea to test jet pumps using the push/pull method also

Not sure what that means

[nmpeter]

good idea to test jet pumps using the push/pull method also

[M@_]

A method I have used with success is using a $30 mighty vac brand pump which can be bought at most autoparts stores (and is even rebuildable and can be used for bleeding brakes) and I have used 5+ layers of clear packing tape over the holes makin sure the surface is spotless and tape goes on with no creases and then bolted the carbs and exh over it to help keep the tape tight,works excellent and is a cheap method if you rarely ever have to do this.

I can't say for sure your intention with this post, but it's very important, and often overlooked, to test an engine with pressure AND with vacuum. Vacuum pumps are available at auto parts stores for about $30. If someone goes through the work to do a leak-down test they should test pressure and vacuum. I've never found a leak with one and not the other, but all of the bottom end seals experience pressure and vacuum.

Cheers,
Matt

[silvercrxsir]

A method I have used with success is using a $30 mighty vac brand pump which can be bought at most autoparts stores (and is even rebuildable and can be used for bleeding brakes) and I have used 5+ layers of clear packing tape over the holes makin sure the surface is spotless and tape goes on with no creases and then bolted the carbs and exh over it to help keep the tape tight,works excellent and is a cheap method if you rarely ever have to do this.

[macGruber]

Who wants the first kiss?

Blocked off the Carbs with a layer of rubber sheeting for shower pan liner cut out in the shape of the triple carb base gasket (minus the holes for the carbs) and another in the shape of the exhaust side of the motor. Cut holes for all of the bolts to go through the new "gasket seals" and mounted the Carbs and exhaust muffler cover (box that mounts to the exhaust manifold). Blocked off 2 of the 3 pulse lines and sent compressed air into the third Pulse and hisssssssssssssssssssssssssssssssss! Out comes all of the air in my engine through a crack in the bottom of the engine. All this top end work for nothing

The good news is that we didn't take the advice of the tech who honed the two cylinders for us and tried the leak down as you guys strongly recommended. This was my buddies engine so you saved me a ton of embarrassment and him a bunch of money. If we would have put that engine in service it would have blown the new pistons and probably worse.

I had the case split open for me because I have never been that deep into an engine and have no idea how to clean and diagnose a bad crank shaft but sure enough, there was melted aluminum on the First Journal and major contamination. These pictures suck but it is all I have. At least now we were able to salvage the 2 new and 1 old piston (great shape) and just have to pay $375 for a crank, $80 for welding fee for the case and $40 or so in gaskets. Labor is only 4 hours to have it torn down and built back up at just $60 here at a local shop so that doesn't sound too bad to me. Much cheaper than $1300 for a new re-man short block with a $150 welding fee at SBT. We'll see how it goes. Thanks again!

[macGruber]

Special thanks to "birdgod" for linking me to this topic. I am helping a bud rebuild the top end on a yami 1200 non-PV right now as a first timer helping a no-timer. The local shop that honed two of the cylinders for us told me that since I am only doing a top end that I have no reason to do a leak down test. I assumed he knew what he was talking about since rebuilding PWC engines is his biz here. I can't wait to torque the bolts down and do this test now. If I have an air leak I'm kissin' someone on the mouth here for the advice! Will report my findings. BTW, is it just me or does this stuff get to be addicting to everyone who busts an engine open in their garage?

Thanks for the gauge build as well!

So it is my understanding that I can simply take a sheet of the appropriate type of rubber and lay it across the tripple carb holes and then bolt the carbs on to seal off that side or is this the area that the air probably must be inserted into? As for the exhaust side, I need to have it removed and then seal off that area. Is it possible to have the pressurized air inserted into my choice of either carb side, exhaust side or right through one of the spark plug holes with the proper fitting up there? Is it not possible to just take out one of the spark plugs and attach the pressure fitting up there? Again, this is a 1200 yamaha off of a 2004 SUV if that matters at all?. I really need to look at those pics from a larger monitor than this cell phone before asking these questions I bet. Sorry if the answer is obvious. Do the pulse lines need to be capped and secured for this as well?

Lastly, I was told to use a thin layer of black RTV sealant on the base gasket for the cylinder but to use an aerosol copper hi-tech (2 spray-on layers each side) on the metal head gasket. What type of sealant is appropriate on the metal and non metal exhaust baskets? Same? Copper on metal and black on paper? Thanks!

[OsideBill]

interesting email him at [email protected] or pm him here lhorning is his screen name.

[Tommykustom]

Yes he does, look in my signature under 2 stroke porting and click on the link it will take you to his website.

Thanks for the quick response Bill. It seems to be a dead link.

[OsideBill]

Yes he does, look in my signature under 2 stroke porting and click on the link it will take you to his website.