1911cc engine, with L-jet about 7000 miles on it.
I think a short video will help the experts direct me, so I'll shoot one and add it. But until then.....

At idle, last week, I noticed a random KNOCK. Reminded me of what I have heard called "spark-knock". It idles along fine, then I hear a faint "CLUNK-CLUNK, then back to normal.

I had just filled up with what was probably some cheap gas, drove 10 miles to work and heard it. 87 octane, E10 from a non-name brand station that I have used many times in the past with no issues.

at lunch, I added a can of Chem-tool to the full tank, but did not see any improvement over the next few days. At half full, I put 7.5 gallons of 93 octane PURE gas. Knock is still there.

It is hard to tell where it is coming from or if it is external ( fan, pulley, alternator, loose cooling tin)or internal (spark-knock, valve train, crank, etc...), but it is random and I don't really hear it at 3000 RPM.

I'll charge my camera, shoot a video and add it as soon as I can. In the mean time, if you have any ideas, let's hear 'em.

Merry Christmas,

Clark

Something rolling around in the fan maybe?

I hear it very clearly at 53 seconds, 2 big knocks. then a few lighter ones thru the 60. Maybe a single knock at 20 seconds and then maybe at 2:05. I rev it to 3000 for about 1 minute. It is not happening a lot and there is so much other noise. But give it a listen.

Let me know what you think.


https://www.youtube.com/watch?v=7ukzcrnTV7I

With what sounds like 'huffing' to me...When it's running at idle put the bottom of your shoe over the exhaust. The engine should load up, stumble and die. If the noise gets more pronounced you have an exhaust leak.

Easy enough.... but it did die. The ole banana in the tail pipe trick and the engine died.

Can you do a leak down test on it? Maybe a seat is coming loose.

I will have to do all 4 cylinders, right? As mentioned this engine has 7000 - ish miles on it. Plus HAM re-did these heads. So i would think and hope that the seats are better than OEM.

I'll try to get to your suggestion.

Thanks.

I used one of those mechanic stethoscopes. it has a long shaft to insert into the spark plug seal on the tin. I could move it around on the head while the car is running. I did not hear the knock thru the scope while checking all 4.

Have not tried the leak test tho.

Clark

At one point I hear a baffle loose in the muffler.. I hear lots of valve train noise at idle. What are the valves adjusted to, how much rocker side clearance do you have? What pushrods are you using and valve adjusters? What cam?

Thanks for chiming in Jake,

There are alot of different noises going on. I guess I had gotten used to the clicking. Anyway, I bought all that stuff from type4store.com.

Chromoly push rods, solid rocker spacers, 9550 cam, 1.7 rockers with swivel feet.

I plan on checking the valves as soon as I get some fresh cork gaskets. But they were originally set at 0 lash and checked at the 500 mile oil change. I did not document the side clearance.

Clark

Well, it's not detonation, that would not occur at idle, Would be an issue during acceleration at fairly low revs and high load.
Detonation would be several closely spaced "pings" under load, not what i hear at 52 sec. Kinda sounds like something loose down in the crankcase that may hit a rod on occasion.

well you sure know how to give GOOD news....

new years eve eve BUMP.

I had a very similar knock, turned out to be a fraying fan belt. The belt would fail along the edge, and fray off a piece. The peice would slap the fan housing till it, then frayed away. Never saw any pieces lying in the housing, the belt never failed.
I can here the knock in the video, sure sounds like mine did.

So what's the valve clearance? (not side clearance, actual lash)

Finally got some time to check the valves.... Been out of town and have not been driving it.

1Intake was 0.0
1Exhaust was 0.04, adjusted to 0.0

2I was 0.0
2E was 0.0

3I was 0.14. adjusted to 0.0
3E was 0.04, adjusted to 0.0

4I was 0.05, adjusted to 0.0
4E was 0.04, adjusted to 0.0

What do you think?

I plan on verifying each once more Monday night, checking the fan belt as suggested, replacing the covers, then give it a restart and listen.

BTW, I found a broken weld on the tail pipe. There is a plate that attaches the pipe to the muffler. Maybe that was what Jake mentioned about the baffle.

Thanks,

Clark

Whats your idle speed? seems a bit low to me sound wise. Sound is definately NOT spark or top end related, I hear a low freq klunk....

Diddnt sound like the sound occurs at higher engine speed, only at idle. Seems like there is a bit of stumble in the idle cycle as well, so my guess is someting, accessory, mount, ect. is loose. Or..... loose con rod or main bearing. Did you have the crank mic'd? Seems a bit low frequency for piston slap.

It almost sounds like the fan is clunking around and hitting the fan housing. Low idle speed with occasional stumble can cause a clunk if something is loose. Time for the long screwdriver or stethescope, find where it is coming from.

Though a motorcycle engine the aircooled inline 4 of my XS1100 it has exhibited a similar clunk when the idle speed is too low. It eminates from the lower crankcase. Has done it since I bought it in 1984 with 400 miles (a 1979model). Now has 128K with the cases never opened and the sound is still there, has never changed.... I think a magnesium case no water jacket and such make sound transmission more evident. Never identified what it is, but I've dissassembled and rebuild 3-4 others and my best guess is it was the primary chain that connects the crank with transmission. The 914 doesnt have one of those, but my point is some engines have a sound...... Gotta accept it.

Also, mount your camera on a tripod and keep in one place, hard to listen consitently with the camera moving around and getting different sounds from different places.

In the video the idle was high, kinda bouncing from 800-ish to 1200-ish

Crank was not mic'd. Bought it used from Cap'n Krusty. I did a few test fit run-outs with a dial using 1/2 the case and the end bearings.

I Originally thought it was the fan too. Need a large mirror to help me see back there. I don't hear it with the stethoscope on the fan housing.

I need to take the seth. under the car and listen. I am beginning to believe that I will have to accept it.

You are correct, moving the camera made it more difficult. Hey, I did give you some time markers to.

After zeroing the lash I ran it for about 10 minutes tonight and I had a harder time hearing it.

Speaking of checking the valves..... That is one BITCH of a job, especially with the goal to be ZERO.

It is nearly impossible to get your hand in (while holding a feeler gauge) above the HE and beside the suspension ear. And then if you need to loosen, adjust and tighten..... WOW

Is there a trick... besides taking the engine out?

In this case, the smallest feeler gauge I had was 0.04 mm, so I positioned the rocker so the swivel foot would spin, I tried the 0.04 gauge. If it slipped in, I adjusted down 'til the SPIN was a bit tighter.

What else can you do to get to ZERO on the Chromoly push rods?

I'm actually getting ready to do this on my new car: 2270 with chromoly pushrods. Previous owner told me to tighten the valve until the pushrod can't be rotated by hand, then back the clearance off until the pushrod can be rotated.
I'm wondering if someone else has a better/different method, or if that's the best way.

Also, yeah it's a bitch on a 914. It was definitely way easier on my old Ghia where I could just scoot in under the back of the car, and didn't even need to jack it up.

This is correct.
If you have chromolly pushrods, you do not even need feeler gauges.
I verify that you can rotate the pushrod fairly easily with two fingers BUT there is zero detectable "slop" when trying to wiggle the rocker arm.

I found that sometimes just checking "spin" of the swivel foot and thinking that is ZERO is not perfect. Cause then for kicks I tried the the 0.04mm gauge and it FIT. So the very thin gauge not fitting and the foot spin is my double check. I even try to get the swivel foot to require 2 fingers on each hand to get the spin. So I am cramming 2 hands in there.

I will now triple check with the PR spin. I wondered how the non-swivel foot guys checked for zero.

I take the rear wheel off, then reach in along the top of the heat exchanger. My elbow is basically on top of the exchanger, and my forearm more or less lays on top of it. No problem that way.

Try different approach angles.

A couple of the valves I can get to from straight outboard. Some valve lugs I use a shorty screwdriver. Some I use an offset screwdriver. For all of the jam-nuts, I use a deep-offset box wrench.

--DD

Clark I had a similar sound and it was due to the AC compressor being loose. Check the alternator bolts. Most likely something else but I was floored when I tightened the bolts and no noise.

Get it on a lift and listen to different parts of the engine with a mechanics stethoscope.
Dos not sound top end. Agree its not detonation. I doubt its IN the case, given that it is not constant. I had an off center fan at one point but it always made contact at the same time. I actually like the fan belt idea. Is voltage constant?

Were you making the idle change, or was the car doing that?

What is the state of your engine mounts? Maybe one is loose?

Where are you suggesting I check the voltage?

I think have a vacuum leak, so the revs do bounce at times. I rev'd it to 3000, but that is it, IIRC. Could be just me moving the camera around.

I got a mirror and took a look at the fan belt, it looked ok. I am removing the trans, so I won't run it again 'til the Doctor is done. But I will check things and keep a list going. I'll be back under tomorrow and will check the mounts and Mike's idea of the ALT mounts.

Front motor mounts are new, but I can check them easy enough.