Enging started ticking after a backfire

[ApacheNick]

Truck is a 72 GM K-15, 350, SM 465

My truck started making a loud, inconsistent tick after a backfire the other day. It almost sounds like a bad lifter but it's only really noticeable when the engine is warm and under load. With it sitting idling it will tick for a while and then it goes away until you drive it for a few minutes.

Another thing is the passengers side leaves a sooty grey mark in the snow while the drivers side does not and the tick sounds like it is coming from the passengers side.

I don't know if it matters but it has a MSD distributer, headers and full dual exhaust, high rise intake and a vary worn out edelbrock carb. All of this was there when I bought it and I don't know what if anything else was done to it.

Any thoughts on this are super helpful as so far I've been told everything from a bent valve to a bad bearing in the transmission!

[AcampoDave]

A bad plug wire arcing out can make an intermittent tick.

[garyd1961]

It's not a sparkplug wire jumping fire is it. That may explain the backfire also.

Looks like Dave beat me to the draw, lol.

[ApacheNick]

I'll look tomorrow. Some of them are fairly close to the headers...

[truckster]

Exhaust leak. That's why you have soot in the snow. And exhaust leaks often make a ticking sound, especially if they're closer to the engine.

[garyd1961]

Bad carb caused back fire, back fire caused header leak.

[mattfranklin]

Originally Posted by garyd1961

Bad carb caused back fire, back fire caused header leak.

Good one.

[Dead Parrot]

Don't overlook the exhaust crossover in the intake manifold. I accidentally fixed an aggravating exhaust tick when I replaced the intake gaskets to fix a vacuum leak.

Even if your hi-rise intake doesn't have the crossover, the heads still have the port that is sealed by the intake gaskets.

[garyd1961]

You need to find where the ticking is coming from.

[mattfranklin]

What the other guys said. Also...

Back in the late 1980s I had a 350 running at low speed (2800 rpm) under heavy load (WOT) on a dyno while doing some knock work with regular fuel -- we were trying to make it knock and figure out what spark timing would make it knock at different octanes, measuring torque to get BMEP, and cylinder pressure to get IMEP and knock frequency and everything. It made some loud backfires and then started missing. After compression tests it turned out that one cylinder had overheated/bent/warped an intake valve. It was visibly tweaked and not sealing on one side. I was not revving it, so likely no piston contact. But the valve head was canted just enough to not seal. I bought a new valve from NAPA for probably around $10 (30 years ago), touched up the seat with the just one stone of the seat grinder (not 3-angle), and I was back in business.

I have not seen that failure mode since then, but I have also not done heavy knock work since then.

[ApacheNick]

I'll have a look at the exhaust in the next day or so and let you guys know what I find.

Also got a stethoscope so I'll do some poking around and see if I can find where it's coming from.

[weq92f]

Originally Posted by ApacheNick

I'll have a look at the exhaust in the next day or so and let you guys know what I find.

Also got a stethoscope so I'll do some poking around and see if I can find where it's coming from.

Recently I was unable to locate my "tick" with a stethoscope. The reason? It wasn't mechanical...


-klb

[truckster]

Originally Posted by weq92f

Recently I was unable to locate my "tick" with a stethoscope. The reason? It wasn't mechanical...


-klb

A piece of tubing used as a stethoscope works well to isolate exhaust leaks.

[Coley]

...apart from the new ticking sound, is the vehicle starting, running and idling the same?

Or running rough, etc like its missing or something equivalent?

Coley

[jeffahart]

A lot of us old guys are good at detecting exhaust leaks... we keep em plugged. If you are not good at it you can do this.

Plug the exhaust tips with the caps from aerosol cans (tape with duct/gorilla tape). Leave a slight bit of bleed off. Get a spray bottle of soapy water. Start the motor. Spray around the exhaust manifolds and the flanges. You will immediately see the exhaust leaks.

My guess is if you just tighten the bolts on the exhaust manifolds and flanges you will probably stop any leaks. If not, spray.


j

[mattfranklin]

These are supposed to be really good exhaust manifold/header gaskets if it turns out to be a leak:
http://67-72chevytrucks.com/vboard/s...8&postcount=79

I have them on mine and no leaks so far, but I'm just getting my engine dialed in and have not yet had it on the road. The machine shop said they were the best out there.

[ApacheNick]

Well, it looks like exhaust leak is the answer. 4 of 6 header to head bolts on the right side were loose. Tightened them up and the tick went away. I'm going to get new gaskets and bolts tomorrow just so I know it's actually going to stay fixed.

Seems the PO of this truck had a real problem with tightening things lol.

[Killer Bee]

glad that's all it was..

header bolts are notorious leakers, might want to look into premium gaskets and locking bolts like mr gasket or stage 8 from summit, jegs, etc.

good luck!

[jeffahart]

Originally Posted by ApacheNick

Well, it looks like exhaust leak is the answer. 4 of 6 header to head bolts on the right side were loose. Tightened them up and the tick went away. I'm going to get new gaskets and bolts tomorrow just so I know it's actually going to stay fixed.

Seems the PO of this truck had a real problem with tightening things lol.

Wouldn't bother, if it's not leaking it's fixed, it's a walk away. Torque periodically. Get some wax and spend your time working on that carnauba shine!


j

[YoungPup1977]

Look into some French locks. They may keep your bolts tight.
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