Fluidplay

I've been searching for weeks the source of this knock that seems to be getting progressively louder. At first I thought it was a rod bearing, but have ruled it out as my oil pressure is where it should be once it's warmed up. I even thought it might be piston slap...GOD I hope not, just had the engine rebuilt...still not sure, though if it were bad bores and/or rings, I should be burning oil and getting some blue smoke out the tailpipe?? Right? I check the plugs and they're dry, though they look like they have a little carbon build up. I'm hoping it's a timing issue and can resolved by adjusting the FQS or MAYBE the belt slipped at some point during break-in?

The engine was recently rebuilt with the new Mahle 100.5 pistons. When we measured the pistons, we noticed the wrist pins were not offset as stock are...? which I questioned, but was informed by the (Rennlist) source that these will work well. Machine work was performed by reputable P-machine shop (no names) and rebuild by a highly recommended front engine P-shop.
My A/F ratios bounce around the mid 14's to low 15's and at full throttle drops down to low 11's-high10's. I changed the TPS and re-sealed the ISV with little change. When I take off in first gear there is a series of knocks that goes away at higher rpm's. I really can't tell you if it still knocking through 2nd, 3rd etc... road noise, bad hearing? I've put approx. 600 miles on the engine to date running this way.

The car ran very rich for the first hour or so of life, then went VERY lean for a brief 60 second run while I was figuring out the piggyback FC. Since then I've been driving it as stated above. Just thought i'd throw this in for some history.

My car is an 86 951-engine mods include:
LR Super 61 turbo
LR Dual WG
55# Siemens
MAX951 chips (had them re-checked for set-up)
Piggyback FC
HV fuel pump
LR Stage II MAF
Venturi Delete

Apologize for the length...hoping you guys can really help me with this, it's insane after so much time and stress not to mention the $$$$ that this thing is running the way it does.

THANKS in advance for any advice, wisdom and direction.

caster951

Where is the noise coming from, the top or bottom of the motor? Could it be the lifters?

lee101315

A very similar sound appeared on my car recently. I was totally sure it was a rod bearing...until I took a closer look. I removed my timing covers, and began to turn the engine. I could literally see the cam sprocket kicking back as the engine spun, making the noise. It was the woodruff key on the camshaft that had worn down...very easy repair. I had an n/a cam tower lying around, so I just swapped it in.

I was seriously about to disassemble the engine until I took a closer look. Good luck

Fluidplay

I've taken a stethoscope to every part of the car...the cam tower, cylinder head, headers, pumps and even the oil pan. Definetly not the lifters, though they're making a little more noise than i'd like, I couldn't determine exactly where the knock is coming from. It's definetly more noticable/louder when I take off in first gear, but I can hear it at idle.

Lee101315 - did your knock go away when you raised the rpm's or continue?

333pg333

Have you contacted LR to see what they say?

lee101315

It would fade in and out as the rpms increased... the noise would disappear when I kept it at a steady 3000rpm, and then make the noise as I decelerated. It really sounded like a rod bearing... I was very close to pulling the oil pan to check...

ShApE

the same thing happened on my roommates n/a 944. It turned out to be the cam woodruff key

eniac

Check that the bolt on your cam gear is tight before you drive it any further.

rlm328

Check for an exhaust leak. They make a knocking noise while you are inside the car or if you are listening to in a confined space like a garage.

KuHL 951

Once on a fun run a driver pulled over for what sounded like a definite rod knock. Ten fairly smart guys all agreed. Turned out to be a cracked valve spring. The dead give away it wasn't a rod bearing was letting out the clutch slowly with the parking brake on; if it's a rod bearing it's gets much louder and deeper sounding. A loose spark plug or exhaust leak sounds pretty evil also.

Fluidplay

Steve- I'll try this..."The dead give away it wasn't a rod bearing was letting out the clutch slowly with the parking brake on; if it's a rod bearing it's gets much louder and deeper sounding. A loose spark plug or exhaust leak sounds pretty evil also." Just to definetly rule out the rod bearings.

Eniac - will check bolt after work tomorrow...

It's not the exhaust, though I do have some small leaks at a couple of the slip fits.

If it was the woodruff key...wouldn't it just continue to make that sound thoughout the rpm range? Is there a way to check it with out removing the cam gear?

Thanks for your input guys, very appreciated.

lee101315

Something to note about rod knock.

A rod bearing failure doesnt make much noise in its early stage with cold oil(except for the intial knock-knock-knock while building oil pressure). It is always present while hot... and if its bad enough, it will knock at all times, cold or not. It shouldnt make too much noise if you keep a steady 2500rpm, but it will knock a few times returning to idle, or revving up (in neutral).

You could also pull spark plug wires one by one while the engine is running and see if the knock disappears. Example, if it is knocking badly at idle and suddenly the noise nearly disappears when you pull the number two wire...its not looking too good for you. I drove a car I once bought with a spun rod for 50 miles this way, and without shooting the rod cap through the block with this technique.

If you catch a spun bearing early enough ( and I mean right after it happens ), you can drop the oil pan, clean the rod journal, and slap on a new set of rod bearings without pulling the engine.

Fluidplay, I think you should do some checking when you get home. Its probably not a rod bearing.

rlm328

One more item, and that is the hydraulic lifters. If they are bad they will make a pretty good racket.

Fluidplay

I'll test the cylinders by removing the plug wires tomorrow too, though I'm really leaning away from rod bearings. The knock is really only apparent when I take off in first gear. Doesn't mean however, that it's not still there.
rim328- I don't think the knock is from the lifters, it's a low sounding knock and there are maybe 6 or so knocks before it quites down. I really can't hear if they continue each time I shift.

xrad

had a similar knock at low rpms , went away over 3000. It was pretty obvious, sounded like a metal hammer in the engine. turned out to be piston slap and cracked ring (which all started due to a head gasket leak).

If you can get your hands on a flexible bore scope, I would take a look before running the engine any more. There was scoring in that cylinder on my engine.