Propane Into Valve Cover... Looking For Vac Leak... Is It SAFE??

[Guest Mike]

I'm looking for a vacuum leak in my Gen1 SBC. I've replaced all hoses and checked the carb, brake booster, etc. I sprayed every seal with starting fluid... but this doesn't tell me if there's a leak in the lifter valley.

 

I read a post in which someone had removed the PCV valve form the valve cover, plugged the hose and ran propane through the valve cover. Supposedly this will tell me if there's a valley leak.

 

QUESTIONS: Is this safe? Could I blow my engine apart? Does this find a valley leak?

[veritech-z]

How exactly is that supposed to tell you if there is a leak?

[Guest jmanz6]

The big boom will tell you where it is.....????

[jnjdragracing]

What are you symptons? I had a bad vacuum leak and it was because my intake was not matching up to my heads. At high rpms it actually was sucking oil from my lifter valley. I had to make transition plates to adapt the intake to the heads. Just an Idea....

 

Not sure about the propane idea......

[Twoeightnine]

Just say no!

[Pop N Wood]

Propane is a time tested method of checking for vacuum leaks. If there is a leak, the extra fuel in the intake will affect the engine idle.

 

I used a can of starter fuild to find the vacuum leaks in my SU throttle shafts.

 

Not so sure about filling the crank case with propane though. Using an unlit torch on the engine externals is pretty safe. But how will you ensure it doesn't build up to an unsafe concentration in the crankcase?

[MONGO510]

To check for an internal vacuum leak, seal the crank case and put a vacuum gauge on it. propane works good for external leaks. Try to divert the air from the fan so that the propane is not blown around. If the enginesucks up any propane thru a leak it will speed up. Do not use starting fluid or lots of highly flammable liquids unless your fire insurance is paid up. BTDT!!

[Guest Mike]

How exactly is that supposed to tell you if there is a leak?

 

From the responses here, I'd say this is a bad idea. But I figured that :^)

[Guest Mike]

The big boom will tell you where it is.....????

 

Well... if the boom is big enough, at least it won't hurt for too long.

[Pop N Wood]

It will tell you if there is a leak when the engine idle speed changes.

 

It is just questionable how safe it might be.

[Sparks280zt]

grumpuvette has recommended this method so that makes me think it is very safe.

[veritech-z]

I don't know, I remember reading how Grumpy took care of a bug problem once...

[Sparks280zt]

Your right hes only an engineer that everyone turns to for v8 answers....

 

But yes, the bug thing was funny, lol

[Pop N Wood]

I don't know, I remember reading how Grumpy took care of a bug problem once...

 

LOL

 

If you switch to ether instead of propane it might take care of the bug problem at the same time.

[veritech-z]

I was just joking, I've got all the respect in the world for Grumpyvette.

[Guest Mike]

What are you symptons? I had a bad vacuum leak and it was because my intake was not matching up to my heads. At high rpms it actually was sucking oil from my lifter valley. I had to make transition plates to adapt the intake to the heads. Just an Idea....

 

Not sure about the propane idea......

 

Rough idle, backfiring through exhaust, can retard dizzy until engine nearly dies, then it can backfires through exhaust AND carb... really weird!!! All new exterior timing components, all new vacuum hoses. CR is within 7 percent on all eight cylinders. Tested for vacuum leak with starting fluid. The only things left to check are valley leak, carb, and timing chain.

[Guest Mike]

Propane is a time tested method of checking for vacuum leaks. If there is a leak' date=' the extra fuel in the intake will affect the engine idle.

 

I used a can of starter fuild to find the vacuum leaks in my SU throttle shafts.

 

Not so sure about filling the crank case with propane though. Using an unlit torch on the engine externals is pretty safe. But how will you ensure it doesn't build up to an unsafe concentration in the crankcase?[/quote']

 

...and found no leaks. However, this doesn't tell me if there's a leak hidden in the valley area. Unsafe build-up of propane is my worry too.

 

I'm just trying to save time and $$$ by eliminating the cheapest/easiest solutions first. I guess the next step is to borrow a carb to see if that's the problem. After that, I'll install new intake gaskets. If that's not it, I'll try a new timing set. If that's not it, then I'll rip the top off the SBC and spit down it's throat!!! Uh... I mean I'll inspect the cam.

[Guest Mike]

To check for an internal vacuum leak, seal the crank case and put a vacuum gauge on it. propane works good for external leaks. Try to divert the air from the fan so that the propane is not blown around. If the enginesucks up any propane thru a leak it will speed up. Do not use starting fluid or lots of highly flammable liquids unless your fire insurance is paid up. BTDT!!

 

Are you saying that the crank case shows no vacuum unless there's a valley leak? Is there a general guideline as to how much it should/shouldn't have?

[Guest Mike]

grumpuvette has recommended this method so that makes me think it is very safe.

 

...I'll ask grumpy.

[jt1]

posted by Mike

 

Rough idle, backfiring through exhaust, can retard dizzy until engine nearly dies, then it can backfires through exhaust AND carb... really weird!!!

 

Check and make absolutely certain #5 & 7 plug wires aren't crossed, or that any spark is jumping between these two wires. A dark garage is best for checking for sparks jumping wire to wire.

 

John