What's this noise? Newly rebuilt 930 engine.
 

Finally got this 76 930 engine back in and running (thanks to those that helped me overcome other issues). After about 45 miles, I now hear this gawdawful noise coming from the engine. Occasionally goes away-seems to lesson as the engine warms. At first I thought it was a loose timing chain or the fan bearing. This engine has the hydraulic chain tensioner upgrade.
I pulled the timing chain covers off to look at the tensioners/chain, but both looked good and tight. I can't move the tensioners in our out with my hand alone, but can by prying with a screw driver, but they're pretty stiff. Nothing is loose. I turned the engine by hand and can't hear anything dragging.
Unless someone has an idea, I guess my next step is to remove the valve covers for an inspection, and then pull the engine the rest of the way out and dive back into the case.

Listen to it: https://www.youtube.com/watch?v=SgYtetX1QSs&feature=youtu.be

Thanks for any help,
Bob

very odd, sounds like an irregular clatter...

Disconnect the fanbelt, this rules out alternator issues.

Other than that, valve covers off and make sure valves not bent...

Sorry, good luck...

Wonder if valve timing could cause it to run that rough?

The video kind of sounded louder near the fan and distributor. either one of those could be a source of noise and not a huge problem. Get a mechanics stethoscope and poke around in there until you find the source. There's quite a bit of oil in the triangle of death, and a random loose copper washer... Probably not related to the noise, but may be some additional things you need to clean up / address.

Could not get a fix on the noise, but a worn out dist shaft with create quite a racket. The pop off valve can create odd sounds when it is worn out, but I think that happens primarly under load and throttle open and closed.

sounds valve or rocker related. Put the washer back on the oil pressure switch while at it. Will fix the oil leak back there.

Chris

for sure, that is a nice leak you got going there

and get a hose or a pair of mechanics stethoscopes and localize the noise

Obviously not what you want to hear on a rebuild.

There are many sources of noise. Could still be tensioners. That rattly sound seems like poor operating tensioners

My experience was rattly sounds after first 30 miles. Pulled engine and replaced one tensioner.

Also looked at the cam sprockets and changed the number of shims to better align the whole chain path to the intermediate sprockets.

Sounds disappeared. 15,000 miles later. Still no sounds.

During the first rebuild I also polished the shafts that hold the idler arms. They had bushing material smeared on them. Replaced one of the two idlers because the bushings were out of spec.

I did not want any binding or sticking between the idler arm and the pivot shaft.

I’ll pull the distributor and check for play at the gear. This engine only had 40k miles on it, so don’t expect a worn out shaft. All new washers and fittings at the oil leak and wasn’t all that tight. Gave it 1/8 turn, so expect that to help.
I did try holding a large screw driver on several places with my ear on the other. It was damn loud every where!
I’ve already checked/adjusted valves after run in and didn’t notice any valve train issues. Since the engine is halfway out, I’ll pull the covers back off and inspect again. Not sure how I would spot a bent valve? Let me know how. It’s a low compression 930 engine, for some reason I didn’t think it was an interference engine. Kind of hoping it is a loose rocker at this point-heard of them coming loose before.
I have a borescope for my phone and checked back behind the timing chains to ensure they weren’t rubbing on the housings.
Pop off valve? Don’t think I have one.
Hope to do some work on it tomorrow. Appreciate the ideas. Keep’em coming.

Take some more pictures of the various parts you are inspecting. Like the tensioner, idler gear clearance

But this is a 1976. They did not come with factory hydraulic chain tensioners.

Did someone add them? I reread the OP. And yes it has them.


Also a leak down test will confirm things like bad valves, heads, rings. Depending on the level and sound source if there is leakage you will know.

Same piston and cylinders and rods? A bent valve will not necessarly make a noise, but will miss fire and pop back and you can determine with a leak down

All same pistons, cylinders, and rods except one piston/cylinder. Original cams/rockers except one rocker. I weighed new piston/rod set and matched weight with others.
I'll add the leak down and compression tests as soon as I get back out to the shop.

Ok this is embarrassingly one of the more bone headed things I have done but easily duplicated. Did you screw the oil line into the correct hole to feeds the tensioners? Yes there are two holes on the tensioner cover where it screws in perfectly. Don't know what the second one is for but it fits like a glove. No oil to the tensioners will make that noise.

Chris

Verified timing Chain oil lines connected correctly.

I performed a leak down test. #1-1%; #2-3%; #3-0%; #4-1%; #5-0%; #6-16% ! The air escaping #6 could be heard coming out the exhaust. Good chance this is the culprit. Next step is to pull the right side exhaust valve cover and inspect. Gosh I'm hoping for something simple! Stay tuned.

A 16% leakdown is abnormal, but shouldn’t make a clatter...unless the valve is hitting the piston? But would then expect a 100% leak down...

You didn’t drop a nut down that cylinder?

Pulled exhaust valve cover and nothing obvious. Was hoping for a loose rocker which was allowing the valve to close all the way and was making noise. With 6 @TDC, valve clearance “feels” normal (didn’t measure yet).
I’m afraid I may be at the point of further disassembly. Might be best to go ahead and drop the engine completely??

Do a leakdown or compression test first...

Do you have access to a video bore-scope?

Yes, I have a bore-scope.

Someone suggested removing the fan belt in order to discount the alternator. ?

The noise seems consistent with crank rpm, not cam rpm.

When you did the differential pressure test what did plug 6 look like, any signs of being impacted by debris?

Perhaps, with the plugs removed turn the engine over by hand And see if there is a tight spot as though something is between a piston dome and head.