Clank sound on re-assembly
 

Alright,...... now what have i done ? Long block assembled. Timed, rockers on, valve adjusted. When rotating it makes a noise that sounds to me like a piston changing direction in the bore, (if the bore were slightly too big) or if the rod was contacting the skirt.

See video for sound. https://www.youtube.com/watch?v=tj7if7yIwmA&feature=youtu.be

I cannot pinpoint which cylinder it is, even used a stethoscope on each cylinder. If i rotate slowly, the sound is almost non-existant. I have checked piston to valve clearance and i'm good there at 4mm+

Heads where rebuilt, new rings, and one new rod and piston. (used) Motor has been apart for a year and a half.

I'm about to pull out my last hair..... :confused::rolleyes::confused:

Shot in the dark for pin pointing the problem...

Where is the Z mark when the noise happen?

Most likely something to do with the cams. They go “overcenter “ and try to snap forward when a rocker goes over the lobe. Watch the tensioners while the noise happens. Maybe you’ll see something move. Could also be slop between the intermediate shaft gear and the crank shaft gear.

-Andy

Yes, I had a similar thing when putting my 964 motor together.. I thought the tension in the change was changing but it was the valve springs pushing back on the cam lobes at different spots during the rotation.

In your video, are the tensioners engaged? are the pins pulled?

Maybe pull all your rockers out except 1 and 4 and check again...

In the video you can see the tensioner for 1-2-3 side compress each time the noise appears.

Thanks for the suggestions guys. I just tried to pinpoint the sound using the stethoscope again while the GF rotated the engine. I heard a loud click on #2 but could tell it was also coming from other places. I backed all the rockers off and really no change. I guess I’ll remove the rockers now and see what happens.

Is there meaning to this ? Can you elaborate please.

Just pulled all all rockers off (except 1/4) and no real change. Could it be the crank walking back and forth ?

This motor made ZERO noises and had no symptoms before tear down. It only came apart to fix oil leaks and do the typical 100K valve guide love.

bummer- sorry, I do not know.

Sounds like the chain could be hanging up on a sprocket tooth (like at oil pump shaft sprockets) in at least one place. Did you set up the parallelism to spec and were the sprockets in ok shape?

Thanks for the suggestion. Sprockets are spot on, and there is no visible movement of the chains (hanging up) The sound is internal.

The tensioner should not be compressing. If you can compress the tensioner piston easily with a screwdriver, probably the tensioner should be replaced.

If it is soft you could have piston to valve contact or the sprockets not engaging correctly with the chain.

I think the tensioners are soft because the oil has drained out of them. I've measured all P to V clearance and have 4 1/4 mm clearance.

If it were a chain issue, binding, or alignment issue, how would that create a noise, or an internal noise ? Not challenging your diagnosis, just want to understand as i'm new to Porsche engines.

I would not start a motor that had soft tensioners.

Are they new tensioners? Have they been bled?

Info here. http://forums.pelicanparts.com/911-engine-rebuilding-forum/914119-carrera-tensioner-questions-5.html

they are the used tensioners that came out of the motor. I have not bled them. Was following Waynes book, it was rather vague on weather this was needed or not.

noise
 

You can support the LS tensioner idler arm with a rocker shaft bolt and cap between the idler and chain cover housing so the tensioner does not compress then rotate the engine.Ciao

The only thing I noticed from watching the video is that the noise seems to happen at a different point relative to TDC each time. This can be observed because the crank is being turned with a non ratcheting breaker bar. It looks like the noise is advancing 30* ish per revolution. Not exactly sure what that means, but it's the only thing that stood out. If the noise is advancing each revolution its certainly not piston to valve clearance, if it's happening on the same cylinder each time. Does it seem like the noise is moving around to different cylinders?

Yes, that is EXACTLY what i've discerned as well. That's why it's been so difficult to narrow down. I hear it in one spot, go there to listen, and it seems to come from another spot. I'm all on my own with this so it's super hard to rotate the engine and chase the sound.

I don't want to continue with the build if there is a true problem, but i cannot see what could be the issue. The case was not split, the pistons came off, but went back on after fresh rings.

Go back to the one thing you changed, the connecting rod and piston. First the piston, if no dice then remove the rod . As you said nothing was changed,,,,,except for that.

I suppose i'll have to do that, was hoping to not have tear it down again. This will be the 3rd time, and the 5th time i've had to borrow the cam tools. At this point, i'm too embarrassed to ask again. Guess now if i spend the money to buy one, it'll be Murphy's Law that i'll never need it again. LOL

Just a guess - but IF the clanking it is advancing or retarding relative to the crank rotation, following a certain, reproducable pattern, I would probably investigate the following:

The cams are rotating by half the crankshaft speed and almost everything else also moves in sync to the crank movement - but the intermediate shaft (and oil pump) DON'T: the drive gear on the crank has 28 teeth, the aluminum gear on the intermediate shaft has 48 theeth, the chain sprocket on the intermediate shaft has 24 teeth and the chain sprocket at the cam again has 28 teeth. This makes the intermediate shaft rotate 28/48=0,5833 times per crank rotation (and the cams rotate (28/48)/(28/24)=24/48=0,5 times per crank revolution) or to put it another way, it takes 1,714 crank rotations for one turn of the intermediate shaft and pump.

Again, this is just a GUESS and where I'd start to look IF you have a regular advance or retard of your clanking sound relative to the crank and could nail it to these relations...

WOW, thanks panama911 for all that. This is a tough one to monitor as the sound seems louder the faster you rotate the engine. So sometimes it will make the sound but if your in the part of the rotation where you maybe switch hands/grip it can be quieter making you second guess if it was the same sound as before...

I wonder if it could be the rod touching the case or cylinder. Can the rod be installed 180* off, and now its contacting something ?

damn, i don't want to take this thing apart again,.......... but i just ordered up the cam tool and will tear into it next week..... maybe.

well... it's just a guess based on the observation of smokintr6 above, that it would be advancing in relation to the crank (I could not really tell from your video). Make a mark on the end of the intermediate shaft (cover off) and see if you could relate the clank to it's movement...

sticky valves?
 

That sounds to me like a valve snapping back into its seat. Maybe the guides or seals are too tight?

It's random because it's not the same valve every time.

Just a thought.

Edit: I might also check the alignment of the rocker shafts. If they are not aligned properly and the rockers are not moving freely, it might be holding the valve open until the piston gives it a nudge.

That is crazy. To me, at 1st, it sounded like a small end of a connecting rod dropping onto the cylinder to my mind. But the evolving index of the crank indicates that it must be IMS related as panama pointed out.

But what could make that noise IMS related is very baffling.

Maybe a borescope through the oil return tube bosses?

It can’t be a valve as it’s a 4 cycle motor. You’d only hear the noise once per 2 crank revolutions, not 4 times per revolution.

Plus, the angle of the crank would repeat every time every 2 revolutions when the noise occurs.

Check the right side chain. Mark it and see if the noise happens at the same point each time in the chain movement. Maybe a link not engaging the sprocket smoothly? That would cause the tensioner to move also.

Great point. Maybe the tensioner is being compressed bottoming due to the chain?