1989 Blaster Engine Rebuild - Part 13

Part 1 - Part 2 - Part 3 - Part 4 - Part 5 - Part 6 - Part 7 - Part 8 - Part 9 - Part 10 - Part 11 - Part 12 - Part 13 - Part 14

 Leakdown

Two-Stroke Software Review

Part 1

Leakdown With the engine plugged up tight I checked it for air leaks. I put a spark plug in the head and torqued it to spec, an expanding plug in the exhaust manifold and I clamped the intake plug with the pressure tube in place. I've sprayed plenty of Simple Green on the outside of the engine - because it foams up so well if any air tries to escape.
The expanding plug seals up the exhaust port. That's not a leak there - that's just the soapy solution settling down.	Things look good all around the engine except for this area - there seems to be something happening here.
When pumped up to 8 psi it is easy to see the leak coming from around the reed cage area - the bubbles make it very clear. More specifically it is leaking from between the outer intake manifold and the reed cage. This is the only area of the engine that's having trouble sealing.	The engine assembles so much better with the small hex head bolts instead of the Phillips screws - it looks better too. I made a plug to cover the oil injection tubes. I don't have that part of the engine but I'll bet there's a plug already there and it needs just a little silicon to prevent dirt and water to enter through it.
Tiny Bubbles It's foaming at the mouth! This simple, yet often overlooked procedure can spell disaster with a freshly assembled engine - or any engine for that matter. A leak like this will often go unnoticed and will be compensated for by richening up the idle mixture screw a bit and fiddling with the other jetting circuits. While this is not a huge leak, it is a persistent one just the same and ANY air leak on a two-stroke is a bad thing. Air leaks mess with jetting, cause erratic running and a noticeable change in its behavior. I watched the bubbles come out of this area of the engine for several minutes (about 5) and the pressure only dropped 1 psi during that time. Ideally I will pump 8 psi into this engine and it should hold it for at least 10 minutes - that means it will hold the pressure without losing any pressure at all. Since it is freshly assembled with all new seals it would not be uncommon to find it to be air tight for a much greater period of time than what's indicated. This leak caused me to make another trip to the shop to order more parts. The built in O-ring that comes on the intake manifold is old and hard and is obviously not doing its job. To prevent me from having to buy a new one I'll install a gasket between the manifold and the reed cage as well as between the reed cage and the engine. It'll seal the next time I perform this test.

1989 Blaster Engine Rebuild - Part 13

Part 1 - Part 2 - Part 3 - Part 4 - Part 5 - Part 6 - Part 7 - Part 8 - Part 9 - Part 10 - Part 11 - Part 12 - Part 13- Part 14

Leakdown 

Two-Stroke Software Review

Part 1

Date Last Modified: 11/29/2011
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