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Posted by: narino Jun 5 2010, 06:04 PM

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!

Posted by: Lennies914 Jun 5 2010, 08:37 PM

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

Posted by: kg6dxn Jun 5 2010, 09:26 PM

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.

Posted by: charliew Jun 5 2010, 09:42 PM

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

Posted by: kg6dxn Jun 5 2010, 09:50 PM

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...

Posted by: hot_shoe914 Jun 5 2010, 09:58 PM

Posted by: SLITS Jun 5 2010, 10:19 PM

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.

Posted by: McMark Jun 5 2010, 10:25 PM

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.

Posted by: Brodie Jun 6 2010, 10:55 AM

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

Posted by: jmill Jun 6 2010, 11:11 AM

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.

Posted by: aircooledtechguy Jun 6 2010, 12:47 PM

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).

Posted by: sean_v8_914 Jun 6 2010, 01:27 PM

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.

Posted by: narino Jun 6 2010, 02:04 PM

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!

Posted by: kg6dxn Jun 6 2010, 04:32 PM

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.

Posted by: Jake Raby Jun 6 2010, 06:03 PM

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.

Posted by: Eddie914 Jun 6 2010, 07:52 PM

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.

Posted by: tornik550 Jun 6 2010, 08:04 PM

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

Posted by: Jake Raby Jun 6 2010, 08:23 PM

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

Posted by: Cap'n Krusty Jun 7 2010, 08:44 AM

Who is the rebuilder?

The Cap'n

Posted by: detoxcowboy Jun 7 2010, 08:51 AM

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

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

Posted by: sean_v8_914 Jun 7 2010, 10:27 AM

I dont think my 103s are that loud...maybe Im used to hearing it now 3 seasons later. we had an "issue" at AX this sat so the motor is torn down to the long block. Ill ifre it up and report back in a few days. we do have to run a loose bore to survive as Jake says. cast pistons can be run tighter.

Jake: does stroke affect that knock? we run a 103 x 71. he has a 78mm crank.
steeper rod angles?

Posted by: Jake Raby Jun 7 2010, 10:41 AM

Yes, the stroke changes the rod angle, which can impact the "knock" greatly with the large bore.

Thats why its all in the combo.

Posted by: narino Jun 7 2010, 11:29 AM

Just talked to the builder and he was more than happy for me to bring the car back by to check it again. As Jake mentioned, he said the engine would be loud because of the clerances until it warmed up. If the noise persisted after warm up then something isn't right.

Capt'n - the builder has been responsive thus far I wouldn't want to post thier name yet until I see how they deal with this issue. I'll post how they folllow up on warranty repairs and such.

Jake - Thank you for dropping in and posting your insight It's much appreciated. I'm pretty sure it's exactly what you mentioned on the cylinder to piston clearances. Yes they were JE forged pistons.

He didn't have notes on the deck height, though he said the cylinder to piston clearance was JE's manufacture specs. The engine was built over a year ago, but had sat uninstalled until 4 months ago. No fault of the builder, my previous mechanic turned out to be a nightmare.

I'm going to try to take the car in this week. I hope it's an easy fix. *crossing fingers.

Posted by: Jake Raby Jun 7 2010, 12:26 PM

Good for you to wait till see how things work out before posting names.. Thats the kind of courtesy that I always appreciate when things don't go perfectly with a client/ build. Its only fair to work this way.

I don't really know what the MFR specs would be on the pistons, I've never known JE to have standardized numbers for this.. Plus the total valve/piston clearance is directly impacted by deck height. If the deck height is unknown, then there is no way to know the actual piston/ valve clearance.

But it still sounds normal for a big bore 103 set up

Posted by: narino Jan 5 2011, 07:21 PM

Ok bringing this one back. After paying off some car debt and driving the car around it's still too loud for me.

I've talked to the engine builder and he says he'll swap out the forged pistons for cast iron pistons with tighter tolerance. He is not charging for the piston swap and would only charge labor to do the work, which is about $650.

Does this price sound reasonable? Also, are cast iron pistons really more quiet and worth swapping out the forged pistons for a more quiet no-track, non turbo'd engine?



Thanks in advance.

Posted by: rick 918-S Jan 5 2011, 09:05 PM

Is he going to balance the assembly again? Heavier pistons, Not cast iron though... more likely cast aluminum?... Heavier = more stress on the rotating assembly. But the piston expansion rates should be more equal with the cylinder material.

Posted by: karlo Jan 6 2011, 01:47 AM

Forging eliminates metal porosity and improves ductility. With the extra strength, forged pistons can be made a little lighter. The improved ductility will allow them to handle knocking a little better.

Whether or not forged is needed depends on compression ratio, max rpm, power output, etc.

Most forged pistons expand more than cast, so need to run greater clearances when cold, and will be noisier on startup.

Posted by: Vacca Rabite Jan 6 2011, 08:33 AM

$650 is probably a deal to have the work done, considering he is going to have to re-balance, redo deck height and maybe even redo pushrod geometry.

Zach

Posted by: Root_Werks Jan 6 2011, 09:47 AM

Posted by: narino Jan 6 2011, 12:58 PM

Again, thank you guys for your replies.

Vacca/Root - glad to hear it.

Rick - I'm pretty sure he'd balance the assemlby again. But of course will confirm this with him. My mind assumed iron when he mentioned cast, but honestly I don't know specifically what material it is not that you bring it up. I'll ask about it as well.

Karlo - He did mention what you've posted. The power output was in a lower range for him to not worry about the definite need for forged pistons. As It's not going to be tracked, and my biggest concern was noise he thought this swap would be best for me.

I guess after the swap to cast pistons could I expect a slight performance drop as the pistons would be heavier and wouldn't rev as fast?

Posted by: Vacca Rabite Jan 6 2011, 01:55 PM

If you are not pushing the car, I kind of doubt you will notice it.
But, I've been wrong before.

Zach

Posted by: realred914 Jan 6 2011, 02:15 PM

if it is too much noise for you ask to hear one of this builders motors with cast pistons first, it may not be that much quieter, intake nad exhasut can make a big noise differenace.

Posted by: narino Jan 6 2011, 02:30 PM

Builder says as long as the piston all weigh the same the is need to balance the assembly? Does that sound right?

realred - Good idea ill see if he has an engine I can hear.