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elpres
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PostPosted: Thu Sep 16, 2021 7:01 am    Post subject: Engine noise Reply with quote

Hey guys.
Im struggling with a weird “exhaust like” sound.
Valve gaps are set, timing fine, nice idle, doesn’t seem like an exhaust leak. The sound comes out from the exhaust pipe tip
But when I pull the #4 ignition cable while running, the sound disappears!
Any pointers? Ideas?

https://youtube.com/shorts/1t7YPvhNCt4?feature=share
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Wildthings
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PostPosted: Thu Sep 16, 2021 11:48 am    Post subject: Re: Engine noise Reply with quote

elpres wrote:
Hey guys.
Im struggling with a weird “exhaust like” sound.
Valve gaps are set, timing fine, nice idle, doesn’t seem like an exhaust leak. The sound comes out from the exhaust pipe tip
But when I pull the #4 ignition cable while running, the sound disappears!
Any pointers? Ideas?

https://youtube.com/shorts/1t7YPvhNCt4?feature=share


Done a compression check?
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Danwvw
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PostPosted: Thu Sep 16, 2021 11:59 am    Post subject: Re: Engine noise Reply with quote

I don't think it's anything. serious it sounds to me like an exhaust leak combined with a cylinder that doesn't fire every time it should. Maybe you can isolate it by disconnecting one plug wire at a time.
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mikedjames
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PostPosted: Fri Sep 17, 2021 11:53 am    Post subject: Re: Engine noise Reply with quote

I would do a compression check - if the sound is coming from the tail pipe rather than around the engine, it could be a valve seat problem.
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1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
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Cap10323
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PostPosted: Fri Sep 17, 2021 2:27 pm    Post subject: Re: Engine noise Reply with quote

It sounds like a missfire to me. Step one would be to isolate which cylinder it's coming from and check for compression and spark.

If it has good compression, I'd assume an ignition issue.
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Starbucket
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PostPosted: Fri Sep 17, 2021 4:03 pm    Post subject: Re: Engine noise Reply with quote

Wait until motor is cold, start it and feel around heat riser joints and head exhaust mounts with your hand and you will feel the leak.
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SGKent Premium Member
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PostPosted: Fri Sep 17, 2021 4:29 pm    Post subject: Re: Engine noise Reply with quote

if the sound is a putt putt .... putt ....... putt putt where it skips a beat then you can put ypur hand close enough to the exhaust to feel it at idle but not close enough to be burned. Feel if the pulses are regular or miss sometimes. If they miss and you remove the #4 wire, and the irregular goes away but there is a permanent hole in the rhythm then it sounds like #4 is mis-firing. All the advice given by others is valid. It could be mechanical but it could also be a bad spark plug, an air leak on that cylinder, a bad plug wire, or even a distirbutor cap. You can start by inspecting it at night in the dark, being careful of any belts and hot things - no long hair etc near the engine, loose shirt sleeves, and see if there are any electric arcs on number 4 wire in the dark. They will be really visible in the dark if it is happening. If misting the wire with a fog of water from a misting bottle makes it worse then it is probably a wire. Plugs and distributor caps can do it too. So can a sticking valve or loose seat but you normally hear that valve noise too when it happens.
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elpres
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PostPosted: Sun Sep 19, 2021 11:57 am    Post subject: Re: Engine noise Reply with quote

SGKent wrote:
if the sound is a putt putt .... putt ....... putt putt where it skips a beat then you can put ypur hand close enough to the exhaust to feel it at idle but not close enough to be burned. Feel if the pulses are regular or miss sometimes. If they miss and you remove the #4 wire, and the irregular goes away but there is a permanent hole in the rhythm then it sounds like #4 is mis-firing. All the advice given by others is valid. It could be mechanical but it could also be a bad spark plug, an air leak on that cylinder, a bad plug wire, or even a distirbutor cap. You can start by inspecting it at night in the dark, being careful of any belts and hot things - no long hair etc near the engine, loose shirt sleeves, and see if there are any electric arcs on number 4 wire in the dark. They will be really visible in the dark if it is happening. If misting the wire with a fog of water from a misting bottle makes it worse then it is probably a wire. Plugs and distributor caps can do it too. So can a sticking valve or loose seat but you normally hear that valve noise too when it happens.


A lot of good advice right there. Thanks
I did take dizzy, cable and plug from another engine without any change in the putt putt putt sound.
Next I will go after the regularity of the sound.
I don’t hear any mechanical sound I think..

I’ll post my finding.
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mikedjames
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PostPosted: Mon Sep 20, 2021 10:13 am    Post subject: Re: Engine noise Reply with quote

When an engine has an exhaust valve leaking, you may also be able to hear a periodic louder hissing as you crank the engine with the ignition disabled.



Also the rhythm of the cranking will become uneven as the load on the starter motor is lower on the low compression cylinder.

I found one by accident at our technical weekend - I put a 2000 amp current clamp probe on the starter motor feed connected to a 1995 Fluke scopemeter, and instead of telling the owner that the max current his 2110 was needing to crank was 180 amps for each cylinder in turn, which was the question he asked me to check ..

It turned out that one cylinder needed 180 amps and two needed 150 amps and one needed 100 amps.

A compression test showed basically 10 PSI on the low cranking current cylinder...

This engine made chuffing noises as you cranked it, same as leaving out a spark plug..

A Mofoco head which it turned out had a loose valve seat, and every valve guide in both heads was loose, apart from one which had been fixed with a 0.1mm larger guide at some time in the past.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy
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Wildthings
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PostPosted: Mon Sep 20, 2021 11:16 am    Post subject: Re: Engine noise Reply with quote

mikedjames wrote:
When an engine has an exhaust valve leaking, you may also be able to hear a periodic louder hissing as you crank the engine with the ignition disabled.



Also the rhythm of the cranking will become uneven as the load on the starter motor is lower on the low compression cylinder.

I found one by accident at our technical weekend - I put a 2000 amp current clamp probe on the starter motor feed connected to a 1995 Fluke scopemeter, and instead of telling the owner that the max current his 2110 was needing to crank was 180 amps for each cylinder in turn, which was the question he asked me to check ..

It turned out that one cylinder needed 180 amps and two needed 150 amps and one needed 100 amps.

A compression test showed basically 10 PSI on the low cranking current cylinder...

This engine made chuffing noises as you cranked it, same as leaving out a spark plug..

A Mofoco head which it turned out had a loose valve seat, and every valve guide in both heads was loose, apart from one which had been fixed with a 0.1mm larger guide at some time in the past.


People don't appreciate how easy it is to do a pseudo compression test by just cranking the engine over with the ignition disabled. A few seconds of cranking and you often have a pretty good idea of the engine's condition. Turning it over by hand can be helpful as well as you may be able to hear where the compression is leaking off and tell if the leak is occurring on the up stroke or near TDC.
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elpres
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PostPosted: Wed Sep 29, 2021 9:04 am    Post subject: Re: Engine noise Reply with quote

Did a compression Test
130/130/130/100
So something to work from there.
Thank you for all your great input guys. 👍
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