Big Pin 750 Reseal/Rebuild Questions

[smokeysevin]

I am getting ready to blow apart my 750 to do seals, rings, and, gaskets. I have done a couple of 4 stroke rebuilds but this is only my second 2 stroke and I want to make sure I do it right the first time.

Is there anything in particular that is kind of a gotcha or something to watch out for?

Thanks,

Sean

 

[smoofers]

1. Clean everything thoroughly - Case halves, scrape all gasket/sealant residue off with a razor and scotch bright pad (BY HAND! - No power tools with scotch bright). Acetone all surfaces prior to reassembly.
2. Chase all of your threaded holes/bolts with a tap/die. This makes assembly easier and gives consistent torque values.
3. All gaskets go on dry the first time.
4. Grease the inner lips of your crank seals prior to installing them.
5. Use a thin layer (smeared on with your finger) of Threebond 1211 between the case halves (let cure 24 hours before pressure test).
6. PRESSURE TEST THE MOTOR - THIS IS THE MOST IMPORTANT STEP. (search on here for how to) 8-10 psi for 10 minutes, no more than 1psi drop in 10 minutes is a passing test.
7. If you fail the pressure test, disassemble and apply 1211 to both sides of the offending gasket. Let cure for 24 hours and retest.

That's a quick rundown on my end. I'm sure there's plenty I'm forgetting. Hope this is somewhat helpful.

 

[kevbo]

Add some red loctite to the outside of the bearings if your crank does NOT have orange plastic bands on the bearings.. This will help prevent fretting between the bearings and the case.

 

[smokeysevin]

1. Clean everything thoroughly - Case halves, scrape all gasket/sealant residue off with a razor and scotch bright pad (BY HAND! - No power tools with scotch bright). Acetone all surfaces prior to reassembly.
2. Chase all of your threaded holes/bolts with a tap/die. This makes assembly easier and gives consistent torque values.
3. All gaskets go on dry the first time.
4. Grease the inner lips of your crank seal prior to installing them.
5. Use a thin layer (smeared on with your finger) of Threebond 1211 between the case halves (let cure 24 hours before pressure test).
6. PRESSURE TEST THE MOTOR - THIS IS THE MOST IMPORTANT STEP. (search on here for how to) 8-10 psi for 10 minutes, no more than 1psi drop in 10 minutes is a passing test.
7. If you fail the pressure test, disassemble and apply 1211 to both sides of the offending gasket. Let cure for 24 hours and retest.

That's a quick rundown on my end. I'm sure there's plenty I'm forgetting. Hope this is somewhat helpful.

Exactly what I was looking for. Thanks!

Sean

 

[fastgtfairlane]

I always put a light coat of assembly goo on any paper gaskets before assembly. It makes it easier to get the gasket off without ripping it. Most of the oem kawi gaskets are stamped steel so you install those dry as mentioned earlier. Also blue loctite every bolt and marine antiseize every stud.

 

[WFO Speedracer]

Make sure you install the crankshaft seals in their correct orientation

 

[smokeysevin]

Got the engine all the way together today, bottom end was done last weekend so the sealant is good and set. I am getting a very slight leak from the intake gaskets that seal the manifold to the reeds, the reeds to the block. Any advise on what to use to get it good and sealed? Everything was cleaned up before reassembly but I am still getting a slight leak.

EDIT: I am not too bright, just reread @smoofers post above. I was pressure testing with 10psi over an hour.

Sean

 

[smoofers]

On most of the Kawi motors I've built, the stud holes on the intake manifold as well as the reed to manifold and case to reed area leak profusely. Adding 1211 around the base of the studs and on both sides of the gaskets then results in no discernable PSI loss over a 10 minute test. How much PSI did you lose over an hour?

 

[smokeysevin]

First time I had the exhaust blockoff loose so it lost 10 psi lol. Fixed that obvious issue and retried it which was when I posted ~40 minutes ago. It is currently down 2psi from where it started at 8psi.

Sean

 

[smoofers]

For safety I'd run another test for 10 minutes. Use soapy water in spray bottle to double check for leaks. However, 2 psi over 40 minutes is most likely passing at 10 minutes!

 

[smoofers]

I made this a while ago as an example of a bad leak:

Chris Kowalski on Instagram: "YOU ABSOLUTELY MUST PRESSURE TEST A TWO STROKE MOTOR AFTER A REBUILD!!!! #vintagejetski #standupjetski #superchicken #pwc #2-stroke #rebuild"

34 likes, 4 comments - smoof_customs on June 14, 2020: "YOU ABSOLUTELY MUST PRESSURE TEST A TWO STROKE MOTOR AFTER A REBUILD!!!! #vintagejetski #standupj..."

www.instagram.com

 

[smokeysevin]

For safety I'd run another test for 10 minutes. Use soapy water in spray bottle to double check for leaks. However, 2 psi over 40 minutes is most likely passing at 10 minutes!

I will probably end up yanking it and using some sealant on it just to make sure. Its easy to do at this point since the motor is out.

Sean