rebuilt engine knocking?, engine builder says its normal for big bore 4's? Options

[narino]

Alright I understand these cars don't have the quietest, smoothest runnning engines made, but does this doesn't sound right to me. There is a knocking sound at startup until she's warmed up. Then it smooths out, not completely though still can hear the knock.

The engine builder, who builds racing type IV engines says that the noise is typical with big bore type IV engines. Here is a link to a video, what do you guys think?

video
http://www.narino.com/images/914-knocking.wmv

Here is what the engine currently has inside it: (originally a 1.7)

103 mm x 78 Stroke
2.0 H beam 5.325 (? no idea what this is was on the paper)
G - Cam
44 x 38 Heads

Thanks in advance!

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[Lennies914]

If I were the builder I would want to see and hear it before I ever made a statement like that. Is it a reputable shop? Will he warrant it for a set amount of time or mileage? If so (IMG:style_emoticons/default/driving.gif) (IMG:style_emoticons/default/driving.gif) (IMG:style_emoticons/default/driving.gif)

[Mike Bellis]

does not sound right to me. I think he did not clearance the block enough for the stroker. You should drain the oil and check for metal debris. I bet a rod bolt is hitting the block somewhere.

[charliew]

Either that or just rev it up and hold it it at about 4k for awhile and it will clearance itself.

[Mike Bellis]

Either that or just rev it up and hold it it at about 4k for awhile and it will clearance itself.

Self machining an engine usually never works as expected. But... Is it under warranty? Can you give us the name of the builder so we can aviod him...

[hot_shoe914]

does not sound right to me. I think he did not clearance the block enough for the stroker. You should drain the oil and check for metal debris. I bet a rod bolt is hitting the block somewhere.

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[SLITS]

Why don't you ask how much clearance was used piston to cylinder? They could be set loose with an engine that size. Piston slap until things expand.

Rods are 5.325" center to center (big end to little end)

44 mm intakes, 38 mm exhaust.

[McMark]

Also what deck height. I've seen an engine that had no interference when turning the motor by hand or at low RPM, but would kiss the heads off idle and tick-tick-tick.

[Brodie]

Doesn't sound good to me. Could be piston slap. I'll let some mechanics around the shop listen to it Monday morning. When my volkswagon buddy comes in this next week I will let him listen to it. Was this noise present when you drove it right after the rebuild or did this begin at a later point in time? How many miles have you put on it.

Hang in there you'll get this issue resolved!

Brodie

[jmill]

From your explaination I figured it was just noise from solid lifters. That's not the case from your clip. I'm hoping Jake pops in and takes a listen. He'll know for sure. I can tell you I'd be worried too. That sounds like piston or rod noise. Something isn't right.

[aircooledtechguy]

Also what deck height. I've seen an engine that had no interference when turning the motor by hand or at low RPM, but would kiss the heads off idle and tick-tick-tick.

(IMG:style_emoticons/default/agree.gif) I've seen this exact thing myself as well.

Before jumping to any conclusions though, get underneath it and ensure you don't have an exhaust leak at the heads or leak at the cylinders/heads. These types of very slight leaks can also have an almost metallic-type of sound as well, but are no problem to fix.

Also check the valve covers for the adjusters just kissing the inside of the covers. This is a common error when setting rocker geometry and installing 911 style adjusters (I assume that's what it's running).

[sean_v8_914]

is it cold? hot? change intensity with increaese in RPM?
use a fat pc of hose as a listening aide. this will allow you to pin point location of knock.
clearance issue should intensify sound w increase in RPM.

[narino]

Thanks for the help guys.

Mike - I'm going to drive it a bit this week and then next weekend do an oil change. I'll let you guys know if I find any metal debris.

Ron - I'll ask about the cylinder to piston clearance. This sounds like what the builder said. Though after the engine is hot the knock is still audible. Shouldn't there be no knock? I'll run the car today and take a video of what the engine sounds like after it's hot.

Nate - There doesn't seem to be any exhaust leaks but I'll check again. I don't think they put 911 style adjuster rockers on it, but I'll ask tomorrow.

Sean - The video is taken just as it's started so the engine is cold. As mentioned before the engine smooths out and the knock lessens when the engine warms up. But you can still hear the knock. I'll rev the engine to see if the knock gets louder.

Things I'm going to ask the builder tomorrow:

Cylinder to piston clearance
Deck height
Did they install 911 style rockers adjuster?


Thanks again!

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[Mike Bellis]

If it is deck clearance you can shim the bottom of the cylinder for clearance. You will loose some slight amount of compression but the knock will be gone.

[Jake Raby]

Sounds like the builder used a forged piston set with that big bore 103mm arrangement. The big bore coupled to the forged piston and cast iron cylinder requires excess amounts of piston/ cylinder clearance to function. Basically this is a compromise that allows the 103mm bore to maintain proper clearance through the thermal differentials that begin at start up and constantly change.

This is the reason why I use only LN Engineering Nickies cylinders with any bore larger than 96mm.

Based on the combo you posted I'd say this noise is totally normal with the bore you have.

[Eddie914]

I have owned a number of 1988 BMW M5's. The S38 engine (3.5 liter DOHC 24 valve 256hp) utilizes forged aluminum pistons with a cast iron block. During start-up at cold temperatures a similar sound is present for the first few minutes. I kinda sounds a bit like a diesel.

"Piston Slap" ???

My last one was still running pretty well with 320,000 miles on the original engine.

After five minutes the engine quites down.

[tornik550]

Sounds like the rocker arms are hitting the valve covers. I had this same problem recently. Here is a link to a video of my car with the same problem.

http://www.youtube.com/watch?v=XJ22OsosZI4

[Jake Raby]

If the valve covers were seeing contact from the rockers, the noise would persist at any temperature over any duration of run time.

[Cap'n Krusty]

Who is the rebuilder?

The Cap'n

[detoxcowboy]

Sounds like the rocker arms are hitting the valve covers. I had this same problem recently. Here is a link to a video of my car with the same problem.

http://www.youtube.com/watch?v=XJ22OsosZI4

That sounds the same as the problem video in this thread!!

-then again I am not a CSI but the knocking sounds the same..