leakdown testing = 1st leak

[rd400canuck]

Thank god I bought a leakdown tester from Econocycle. In the past I would have put everything together thinking it was fine then endlessly fought with jetting and wondered why my bike would seize on extended runs on anything faster than 70 kmh/ 43mph no matter what I did with jetting.

So what do you guys do when the intake manifolds and the gasket wont sit flat against the intake of the cylinder? I tried different amounts of torque on the 4 bolts to make sure i wasnt going in too hard and warping them but nothing changed. I guess I could use yamabond but its so messy and super adhesive. How about high temp silicone?

Than you,

John

[rd400canuck]

Also... I dont quite know what the increments are on the dial. What should i pump to and how long should it keep it for?

EDIT.. found my glasses.. it's in MM/HG  which I think is a new one on me but they sent a conversion chart with it that I remembered was in the box.

6 psi = 310 MM/HG

[rodneya]

Need to hold 6Psi for 6 minutes. Some people will accept less than 10% pressure drop, some wont.
Ive used yamabond before on old intakes that the rubber gad hardened and it worked fine. Just put a little on the gaskets so that it does not squeeze out all over the place.

[Dvsrd]

mmHg is just the pressure of an X mm column of Mercury. Often used on barometers, showing ambient air pressure and inducating weather changes.
Regarding silicone sealants, most are not fuel resistant, so not the best for intakes and 2 t crankcases

[Yamaha 179]

There is a distinct possibility that the cylinder manifold itself is distorted from improper tightening of the reed manifolds; it doesn't take much to cause a leak.  Use a known straight object, I use a machinist square, to check that the surface is straight and level.  If there is only a slight gap you can use Yamabond or maybe two gaskets to seal it up.  I have had to have the surface milled to correct the problem.
Lyn Garland

[rd400canuck]

Thanks again guys,

I opted for yamabond just because it's quick and dirty fix. No more air from there.

Pressure now dropping much more slowly. Soap and water tells me now tells me the left cylinder head gasket is the culprit. I cleaned up and used the old ones for the leakdown testing because I didnt want to flatten the new one's just yet. I think I'll just use them anyways since I need to make sure the crank case is sealed properly.

[Greaser Greg]

is it ok to anneal the copper gaskets and re-use them for a test like this?  heat to red and let cool slowly?

[Brad-Man]

Yes - anneal..

[rd400canuck]

Thank you for the annealing idea. I totally forgot about that.

So now the only leaks I can see are around the head gasket. Using the new copper gaskets lessened them so now its so little it just makes like a foam instead of bubbles in a few places. This is at 6 psi so I assume at combustion chamber levels it'd be much more.

I'm off the Canadian Tire to buy some 600 grit wet sand paper to use on a mirror I have and lap the heads flat.

[1976RD400C]

You can spray some of this on each side of the head gasket to help seal.

[SoCal250]

is it ok to anneal the copper gaskets and re-use them for a test like this?  heat to red and let cool slowly?

To properly anneal you need to quench them, not let them cool slowly.

[Striker1423]

Anneal by heating cherry red and dunking in cold water, scrub black scale off gasket surface and use 3 coats of copper coat per side with a minute to set between them. Will solve all head leak woes!

[rd400canuck]

Thanks guys!

[pdxjim]

I have re-used head gaskets lotsa times with just a few liberal coats of Copper Cote.

Annealing is for sure better, but not really crucial if you have the spray.

[rd400canuck]

I'll but some copper coat after work today.

I'm guessing if it still has a slow leak and I cant find it by spraying that means the cases are coming apart for another attempt. That will suck. but now than later after everything is back together I suppose.