Diagnose "Squelching" noise...

[Keith_B]

Hi,

First post so apologies for any broken etiquette here.

I have isolated a "squelching" sound from my van engine - please listen to the video turning the engine over with the starter motor.

- Only affects cylinder 3 when cylinder 3 generates compression (sparkplug/compression tester)
- Engine runs, just won't idle easily

I'm getting close to pulling the engine and head to see what's what - any thoughts from you guys?

Thankyou, Keith


https://share.icloud.com/photos/012oxWXu6NHfhgQlDeeXxAhVg

[airschooled]

Is the spark plug threading in nicely? Valves adjusted to .006" cold?

Sounds like a potentially loose head/cylinder, leaking compression out of a tiny hole. Often times at cold start you'll see puffs of smoke from the junction too. Early on with this, the noise will go away as the engine expands with heat and seals. Run with it for a while, and it may not disappear…

If you're comfortable with the operation, you can remove the rockers and check the tightness of the head stud nuts. M8 threads are 18 ft*lbs, and M10 threads are 23 ft*lbs. Adjust the valves after.

If you get more than an eighth of a turn on any head stud in place, it's best practice to remove the engine tin and retorque all sixteen head studs evenly following the factory sequence.

If it's an original B-code engine, you may have a pulled stud. Around 1971 VW started threading the upper left/front stud deeper into the case so the soft case metal has less chance of stripping. If you try to torque the head nut and find the nut endlessly spinning, strike three 'yer out.

Good luck!
Robbie
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[Keith_B]

Thank you Robbie - I'll go check the head nuts.

I installed "case savers" in this engine a few years ago, so all fingers crossed.

[Keith_B]

Definitely need to check all head nuts torque - two of the lower four head nuts (cylinder 4) were not at the right setting.

So, do I need to pull the engine to do this, or is there an "in van" method to check the top four bolts behind the tin.....

(I think the answer is "pull" the engine)

[Starbucket]

Look at sparkplug #3 for carbon tracks on the porcelain you might have a bad plug.

[Wildthings]

Does the noise go away when you remove the plug?

Maybe start with a compression and leakdown test.

[Keith_B]

It goes away when no spark plug/compression tester screwed in. The compression shows as good, I think the leak is small enough to show compression and enough to show the head is not tightened up to proper torque settings, checking the head nuts that I can get to under the rockers has confirmed this and hence I need to access all the head nuts now....

Planning on pulling the engine tomorrow.

[dodger tom]

[Keith_B]

Cheers - I think I need to get the engine out to remove the tin….?

[Wildthings]

Maybe you have a bad crack or burned out area next to the spark plug?

[Reverand Hope]

initially I thought it sounded more like mechanical contact, like the fan rubbing on the shroud but I'm listening to it on a laptop...

Have you tried turning the enigine over by hand with the plugs in, rocker arm removed, with a stethoscope or tube down the pushrod tubes, and comparing each barrel. Any difference in airtightness approaching TDC would be obvious.
Failing that, some light oil in the plug wells (plugs fitted) may reveal escaping air in the form of bubbles....

[airschooled]

Can you get a cold start video from the same camera angle:?

[Keith_B]

Thank you all for the ideas. The engine is now on my workshop floor being reassembled to be refitted. All head bolts were loose, I’m hoping this will fix the problem. It’s been a good exercise to pull the engine, I’ve replaced all the fuel lines, modified my jack and made a wheeled engine dolly to make the process much easier. Expecting to start her back up next weekend.

[P24p1]

[Keith_B]

Engine went back in over the last day or two, took my time to replace fuel pipes, CV boots, wax the box chassis sections.

And it runs, noise all gone - happy with that and thank you all for the contributions