TheSamba.com :: View topic - Hissing noise from left engine after tune up

Mon Jan 20, 2014 7:12 am

Today I did the following with the engine stone cold:

1. removed plugs
2. checked valve clearances (only no:4 were a bit loose so tightened them up)
3. checked points gap (it was too tight so I opened it up to 0.16'')
4. did a compression test. All cyls were 115-122 psi, so good
5. checked static timing, the light came on for cyl 1 at about 10 deg btdc, so I adjusted that for 7.5 deg
6. checked various nuts - many seemed loose so I tightened up oil pump nuts, heat riser to muffler nuts, j-tube to head nuts both front and back, and castings to head nuts too.
7. replaced plugs

I expected it to be even better than before, but when I started it up, although it idled, it sounded much deeper than before PLUS a loud HISSING was coming from the LEFT side of the engine which had not been there before.

Also the idle seemed to jump around more than before. So I moved the distributor when running back to where it had been before and it idle rpms increased but it still sounded deeper than before.

The only thing I can think of is that in tightening all those nuts I broke a seal of some sort and the hissing is a nasty air leak?

It makes no sense, with excellent compression I expected it to run fine...

Should I try adjusting the carb...? but the old plugs were brown so the carb seems to be at a good setting.

Help please!

Mon Jan 20, 2014 7:31 am

Hissing usually means you've opened up a small vacuum leak. Did you tighten the nuts holding the intake to the head? If so, and you have a DP intake, you could have disturbed the rubber/urethane seals between the intake end horns and the center tube.

You can check for a vacuum leak with a can of brake cleaner. WD-40 doesn't burn anymore, so that trick is out. While brake cleaner is not as volatile as carb cleaner, there's still a very great danger doing this, so care is needed - as well as a handy fire extinguisher. With the engine running, spray a small amount of brake cleaner around the carb to intake gasket, around the seals at the end horns, and at the mating surface where the horns meet the head. If the engine revs at any of these points, you've found your leak.

You didn't mention your type of distributor, but a vacuum canister leak will also hiss at you. Make sure the hose from the canister to the carb is tight on both ends and not split anywhere in the middle.

Mon Jan 20, 2014 7:37 am

drs1023 wrote: Hissing usually means you've opened up a small vacuum leak. Did you tighten the nuts holding the intake to the head? If so, and you have a DP intake, you could have disturbed the rubber/urethane seals between the intake end horns and the center tube.

You can check for a vacuum leak with a can of brake cleaner. WD-40 doesn't burn anymore, so that trick is out. While brake cleaner is not as volatile as carb cleaner, there's still a very great danger doing this, so care is needed - as well as a handy fire extinguisher. With the engine running, spray a small amount of brake cleaner around the carb to intake gasket, around the seals at the end horns, and at the mating surface where the horns meet the head. If the engine revs at any of these points, you've found your leak.

You didn't mention your type of distributor, but a vacuum canister leak will also hiss at you. Make sure the hose from the canister to the carb is tight on both ends and not split anywhere in the middle.
Thanks. Yes I did tighten those metal casting inbetween the heads and the manifold. The rubber boots from casting to manifold are solid though and tight.. I have a SVDA distributor and I suppose I may have knocked the canister when cleaning etc. I'll check that too. It just seems so far-fetched than a a few mm on the head nuts can open up a whopping great hissing sound like that...

Also possible I suppose I haven't tightened one of the plugs enough - no3 never tightens up really well anyway so that might be the culprit.

Well I guess I'll have to spray and find if it is an airleak.

---

On another note, when I hooked up the strobe light (red lead to coil same as condenser, black to a good ground) and pressed the trigger, the engine almost died every time. WTF?

Mon Jan 20, 2014 9:32 am

You don't need a large opening to make a noticeable vacuum leak.

You should be hooking up your strob light to a constant 12v source, usually people draw from the positive side of the coil (not the side the condenser is on).

Mon Jan 20, 2014 2:28 pm

Oh thanks for the strobe light tip.

Well if i have overtightened various bolts would loosening them fix it or have i gone an ruined the flatness of the mating surfaces?

Thu Jan 23, 2014 3:46 am

Hooked the strobe light to the positive size of coil, this time engine didnt die when i pressed the trigger but nothing happened. Have i ruined my strobe light by using it incorrectly?

The engine gets hot on the right, not at all on the left. Right exhaust and manifold casting is hot, left is barely warm.

I sprayed around all the joints but there was no noticeable change in rpms at all, anywhere. It's just unbelievable that I am back to stage one with my air leaks.

I loosened the nuts on the left manifold to head (the ones i had tightened after which this problem happened), same. Loosened and tightened manifold boots, no difference. Still a hissing sound from left engine. When i pull the throttle and let go, it whines or squeals a bit on the right. Can't be healthy to have the left this cool.

I had the left head tapped and re threaded where the heat exchanger bolts onto it at the front (front is front) because before one of the bolts just turned in the threads. It fixed that and was nice and tight but these I ALSO tightened up some more the other day. Should I loosen those too to see if that makes a difference.

I just can't believe that after fixing the stripped head, getting a new muffler, replacing carb and FINALLY getting rid of any audible air leak issue, i have gone back to stage one just by pulling a wrench on all nuts to check for looseness!!! It's not like I can even drive to the garage with the left engine running this cold.

Thu Jan 23, 2014 5:42 am

Edward, check your spark plug location for proper firing order.

Misplaced wires will make for a poor running engine making funny noises.

Find #1 cylinder TDC Firing (both valves fully closed) remember TDC happens once per crank rotation but it takes two rotations to complete a firing cycle. The 2nd TDC has the exhaust valve open to push out combustion gases.

Dave

Thu Jan 23, 2014 1:33 pm

Well if the left side is cold, then it's likely not firing properly on 3 and/or 4. As DJ Keev says check the plug wiring.

Thu Jan 23, 2014 3:27 pm

My experience with no timing light turned out to be a non-firing plug. Thought my light had gone bad. Moved wire pick up to #2 wire and it lit up. Back to #1 and nothing. Replaced all plugs and solved that. Are you certain you have the plugs in tight on the hissing side? A plug not seated completely will leak compression and cause a misfire.

For what it's worth....

Thu Jan 23, 2014 4:50 pm

Hmm thanks all, I will try this all tomorrow. As for the plugs being seated properly on that side, 3 especially will just turn and turn but it has been tight ENOUGH thus far. It's not wobbly at all, but I shall try and tighten it more if checking I have the wires round right way doesn't pan out.

Thu Jan 23, 2014 6:11 pm

If your spark plug wires are in the correct spots on the distributor cap, I'm going with a big vacuum leak on the side that's cold. I installed dual carbs on an engine. I didn't notice that a part of the carb was hitting the fan shroud. The manifold nuts were tight. It wasn't running on that side. I finally saw the bolt hitting the fan shroud and removed it. I then tightened it back down and it ran perfect.

You might pull the manifold loose on the side that's not firing and replace the manifold gasket. Then make sure your boots are not torn or have a hole in them.

Sun Jan 26, 2014 1:29 am

I checked the wire orientation, they are correct. I tightened down plugs 3 and 4 (they went tight this time, not just turning). Started engine and the same hissing. But it seemed like less hissing and the left exhaust seemed to heat up the same as the right. But still, after several minutes the left manifold casting was still stone cold whereas the right was warming up.

I removed wires 3 and 4 and checked for spark, they both had it. So NOT an ignition issue.

I removed the air cleaner when running, passed my hand slowly over the top and the running of the engine didn't audibly change at all. Only when i had a tiny sliver of opening left did thee engine start to die.

So a huge leak? I tried with wd40 that didnt do anything at all. I will need to get some brake cleaner to find the leak then, or just remove the carb, manifold and castings, replace the gaskets and then tighten it all down again. Possibly with the heat exchangers to head and manifold to muffler too...

Such a bummer, it's freezing outside and I am busy enough as it is!! Why o why did i think of touching the head to manifold nuts :roll:

Sun Jan 26, 2014 6:42 am

As my father used to say......

If it ain't broke....don't go fixin' it!

Sorry for your troubles.
It's cold here as well, single digits F and windy!

Dave

Fri Jan 31, 2014 5:26 am

djkeev wrote: As my father used to say......

If it ain't broke....don't go fixin' it!

Sorry for your troubles.
It's cold here as well, single digits F and windy!

Dave
Yep that's a good saying!

Today was warmer so I went ahead and did the following:

Took everything out the engine bay except for the shroud, generator, distributor and manifold. It all needs a clean anyway.

I removed the two end castings from manifold to heads and removed the metal gaskets there. I noticed I had used some silicone when I installed them and it was a bit of a killer to get it all off. Not using silicone again!

The left side was pretty much dry with some gritty carbon (I guess) in the two holes. The right side, which hadn't been causing a problem, was pretty wet though when I removed it, smelled like fuel. It was dark and gunky - see photos.

The real culprit of the hissing sound became obvious when I removed the rubber boots. The left one had a big tear in it under the clip, evidently tightened too much with a not very suitable and sharp clip.

Right side head gasket, gooey stuff seems to be on outside only, no where the holes in the head are - so from spark plug holes?

The tear - this is also the exact location where the hissing was coming from. I guess tightening the head nuts shifted the position of the left boot a tiny bit and subsequently released the tear which sucked in air.

So the facts are:

- I have great compression. My engine is in good shape and only done a few thousand KM.
- Heads are old but seem to work fine.
- Have been through three carbs in attempt to fix erratic idle and inability to set idle at a steady RPM, so carb cannot be at fault.
- Restored, repaired heat exchangers (before it was a weak join between left exchanger and head)
- New muffler.
- Even if I fix this new AUDIBLE air leak evidently caused by the tear in the manifold boot, I suspect I may have leaks elsewhere due to never being able to get it to idle at a steady RPM.
- SO, I think I should get a new manifold along with the new rubber boots and gaskets, as this is the only major remaining unchanged potential culprit to air leaks. (Already done a carb change, fixed head to exchanger joins and got new muffler). When I cleaned the manifold during the engine rebuild I hit it about with a rubber mallet to get out the carbon. There are also some cracks in the central alloy casting bit so I bet there's at least one hairline crack that is affecting idle but too small to actually hear.

Oddly the little spring thing on the inside of the distributor cap has broken off, how the hell can this happen? It was bosch!!

Lastly, I have these as spare. There are so many mixed reviews on silicone, black rubber, OG rubber and urethane boots I figured using these ones which are FAR fatter should get rid of the issue of cracking and cutting the rubber with the clamps. Thoughts?

Fri Jan 31, 2014 6:49 am

I have the silicone boots on my 1600 in my '56. They're probably 8 years old now and are still in perfect condition. Be careful when buying them as some are just red rubber.

When I first bought my '56 it had those split boots on it and they worked fine and never leaked.

Wed Feb 05, 2014 10:10 am

That's good then! Cheers.

I removed the fan shroud today and the intake manifold. Really seems like it is good condition. I can breath through the heat risers but not completely easily - need to use a bit of pressure. Is that OK or do they need to be totally clear to work properly?

I blocked all ends and breathed down everywhere to see for cracks or splits where air might be escaping and there are none. I reckon the manifold is good to use. I also sanded all mating surfaces to as smooth as I could get them. I'll go ahead and put it all back, with some loctite gasket sealant around the head gaskets as soon as I can.

Should I paint the bare steel on the manifold?

Are these little pock mark holes an issue? There are no leaks in the manifold so I guess these are just defects in the outer casting..

Wed Feb 05, 2014 10:20 am

Painting that'd need HIGH temp paint. Use new manifold to head metal crush gaskets and torque the manifold on evenly. You shouldn't need a sealant there and it'll be in a very hot place so if it deteriorates it'll maybe cause a leak.

Wed Feb 05, 2014 11:35 am

Glad you found your vacuum leak!
I'll bet the car runs better now that it is fixed.

That heat tube, yeah it should be clear the whole way, no obstructions.

Chuck a piece of steel wire cable in a drill and feed it through as it spins. The un stranded ends will beat and scrape that carbon out of the pipe.

Dave

Wed Feb 05, 2014 12:18 pm

Ok then! No sealant, and i'll wire drill out the remaining carbon.

I have sone high temp paint. I think i'll use body filler to fill those ugly pits in the heat risers, then sand and paint.

Wed Feb 05, 2014 3:18 pm

emu88 wrote:
I have sone high temp paint. I think i'll use body filler to fill those ugly pits in the heat risers, then sand and paint. Good luck with that. :D