Author Topic: Exhaust Popping?  (Read 477 times)

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Offline Matt G

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Exhaust Popping?
« on: March 08, 2020, 07:13:48 PM »
Hi guys, just curious to understand a phenomenon that happened recently. My Ď70 was a little harder to start than normal (it had been a while between starts...) and when I did get some life, it settled down to an pretty normal idle, however it was popping (almost more like a backfire) out of my right side exhaust pipe. Frequency was probably every second or two. I parked it back in the garage for a later check/review.
Today I pulled all the plugs and the right side (cyl 2/4/6/8) were pretty even, but all were wet/oily. The left side (cyl 1/3/5/7) were a little carboned up ( similar to the right) but mostly dry.  I gave them all a good clean and loaded them back in. I figured that it was running too rich, so I checked my mixture screws: FL @ 1-1/8 turn from seat), FR @ 1-1/8, RL @ 1-1/2, RR @1-1/8. I screwed in the RL in to 1-1/8 turn, figuring that it may have worked it way out a little, but didnít expect it to change the heavier fuel load on my Right hand side.  I check all of my spark leads and they looked perfect.
Started up okay, however again a little harder than usual. When started, no exhaust pops/backfires were noticed.
Any ideas?

Offline sirfixalot

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Re: Exhaust Popping?
« Reply #1 on: March 10, 2020, 11:31:28 AM »
Sticking valve?

Offline Bfit

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Re: Exhaust Popping?
« Reply #2 on: March 10, 2020, 04:29:06 PM »
 Two saying come to mind when it comes to  motor vehicles

If it ain't broke, don't fix it

 Guessing is cheap. Guessing wrong is expensive.
Bfit 
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Offline Matt G

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Re: Exhaust Popping?
« Reply #3 on: March 10, 2020, 11:54:28 PM »
I think an intermittent valve seat might be close to the problem (after deep thought an many beers). The bit that has me confused it why most of my right side cylinder bank had similar spark plug characteristics.  If it was one valve (logically my exhaust valve in this case) then wouldnít only one cylinder show different characteristics?  Itís highly unlikely that itís all four cylinder 2/4/6/8.
I overheated my ignition box (MSD 6A) back when we had the 46deg day, and she stopped until the flat bed delivered her home (and cash was exchanged 🤬), but  I canít imagine how it would create a cylinder or bank specific issue with firing.

Assuming itís a valve seat or sticky stem seal, is there an easy way to test? I have a braced roller rocker train, but I could test clearances if valve/rocker adjustment is the key problem.  I canít get a cylinder pressure tested in behind my extractors to test variable pressure. Can I buy a screw-in pressure tester? Even better if anyone knows of an electronic logging version...!!!
Any suggestions on how to test for valve stickiness?
If you pm me I can send a video, pics, etc.

Offline Scott

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Re: Exhaust Popping?
« Reply #4 on: March 12, 2020, 08:49:56 AM »
Check exhaust runner temps with an IR temp gun?  Might narrow it down to which cylinder is playing up.

Offline Bfit

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Re: Exhaust Popping?
« Reply #5 on: March 12, 2020, 11:11:19 AM »
yes,
you could try this
 with engine cold , you can use the finger pyrometer test . as exhaust starts to warms up.
DONT BURN YOURSELF if you use this method.  only viable for the first 10 to 15 seconds of engine running.
bfit
 
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Offline gtc

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Re: Exhaust Popping?
« Reply #6 on: March 12, 2020, 05:25:37 PM »
My 1970 454 with solid lifters and stud girdles had a similar problem until I got the valve lash adjusted back to the cam spec. That fixed it.
It's C3 chromie for me, see? Si!

Offline Matt G

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Re: Exhaust Popping?
« Reply #7 on: May 17, 2020, 12:29:05 PM »
Thanks guys, I took her for a good run  sitting on about 3k for a while, and all nice again (plug colours, idle, etc). Obviously a good clean out (not a fanging cleanout close to home) is what was needed. However the valve comment has started a ĎCOVID QUESTí for me and Iím trying to figure out my Cam profile.
Iíve measured my rocker lift (pushrod side) for every 15deg of engine rotation and have a pretty profile graph, but still no idea of my cam model/tech profile. So now Iím all in. Belts, pulleys and water pump are off, and Iím heading for the front end of the camshaft to see if it has the number marked there (Iím told that itís either at the front, back or middle).
However Iíve hit a snag and would love to leverage some experience. My harmonic balancer is on tight. I mean real tight. I purchased a puller (3 bolt version) and it Ďainít budging. Iíve drenched in WD40 and left it for days with the centre bold under tension, but still no movement. I thought about tapping with a hammer yesterday, but I didnít think that it would be okay for the journal bearings.
Any loosening suggestions?

Offline Bfit

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Re: Exhaust Popping?
« Reply #8 on: May 17, 2020, 05:26:10 PM »
Matt
Did you remove the bolt and washer that holds the balancer on.
Bfit
Ps apologies for asking , but Iíve seen that mistake a few times. Also the bolt removed and the washer left in place.
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Offline Matt G

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Re: Exhaust Popping?
« Reply #9 on: May 17, 2020, 08:19:24 PM »
Haha, all good for asking BFit. Bolt and washer are out, buffed clean, cold gal coated ready to go back in. I needed to get this out to pull off my p/steer and alt pulley.  It was tight as well, but saw a good tip on YouTube to jog-crank the engine with a breaker bar, and it came off easy.
Iíve seen mixed messages on USA forums to pull the balancer. Hit the balancer, hit the centre pulley bolt, and heat it up, but I think all of them run risk to my main bearings, so I wanted to check with my local gurus 😁👍

Offline Bfit

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Re: Exhaust Popping?
« Reply #10 on: May 17, 2020, 09:56:12 PM »
Matt
 NO  hammers and no heat it will just wreck something.
 Matt my number is on the forum .
Committee contacts
Ring my tomorrow .
Bfit

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Offline Matt G

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Re: Exhaust Popping?
« Reply #11 on: May 24, 2020, 11:10:58 PM »
Thanks BFit. All of your tips were enormously helpful. Thanks again! For the forum, balancer is off via creating a semi-fake bearing against the end of my crank with a series of greased washers. Worked a treat to reduce friction and ensure that I didnít damage my crank threads with the nose of my puller.
Last question (me being a tight-ass)...  any cheats for rotating my engine when the balancer is removed. The correct tool is a crankshaft socket, but I donít build engines regularly, so buying one is just one more (single use) tools that I probably donít really need to buy. Any easy cheat suggestions? Modified ring spanner, simple insert to something else, or a tip for a location on a HD Plastic option?