Loud knocking when cold starting. (Vid inside) - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


General Miata Chat A place to talk about anything Miata

Reply
 
 
 
LinkBack Thread Tools
Old 09-29-2010, 06:12 AM   #1
Junior Member
Thread Starter
 
Join Date: Oct 2008
Location: Manchester, UK
Posts: 274
Total Cats: 0
Default Loud knocking when cold starting. (Vid inside)

Video of noise

I'm trying to diagnose where a noise is emitting from when I cold start my car. The noise goes within seconds of the engine starting and isn't apparent when fully warmed up or during hot re-starts.

The sound can only be described as a rod or piston wanting to jump out of the engine, but only on cold start ups? From the driving seat it sounds like it's coming from the intake side of the engine. The car drives perfectly fine, and boosts well.
It's almost like the engine wants to throw something off that is loosely bolted to it?

Things I've quickly checked:
The exhaust seems to have no excessive play in it but I've not had it in the air yet.
I did a compression test and results were fine cylinders 1-4 resulted with 192, 196, 189, 191 psi.
All spark plugs are a nice tan colour.
I've checked the crank pulley for wobble.
I've also checked the throttle body butterfly on Richy's advice for impending implosion and it's rock solid with zero play.
I've checked the intake manifold and brace bar.

Things to check:
Starter motor?
Alternator being secure to block?

During the compression test, the starter sounded really rough and weak when rotating the engine.

Basically tell me that it's NOT big ends or some other major engine internal and I'll love you for a bit.
CRAIGO is offline   Reply With Quote
Old 09-29-2010, 07:04 AM   #2
Cpt. Slow
iTrader: (25)
 
curly's Avatar
 
Join Date: Oct 2005
Location: Oregon City, OR
Posts: 12,107
Total Cats: 518
Default

Motor mounts?
curly is offline   Reply With Quote
Old 09-29-2010, 09:15 AM   #3
Junior Member
iTrader: (4)
 
Join Date: Sep 2010
Location: Australia
Posts: 168
Total Cats: 10
Default

Wow, weird.

If it was a big end, it would probably knock for longer than a few seconds.

The fact that it goes away quickly tends to indicate that whatever is causing it is as a result of a lack of lubrication. Once the oil pump gets oil to the location, the noise stops.

How many miles has the engine done? Has it ever been apart? Could it be piston slap or something?
zossy1 is offline   Reply With Quote
Old 09-29-2010, 09:18 AM   #4
Junior Member
Thread Starter
 
Join Date: Oct 2008
Location: Manchester, UK
Posts: 274
Total Cats: 0
Default

Yeah I've been told on the UK Nutz site that it sounds like the exhaust knocking. It sounds like this to me too, but seems to come from the engine bay. The fact it doesn't knock when re-started hot suggests something is expanding and stopping the noise occurance?

The mileage is 58k miles, and motor (internally) is stock.

I'm going to check the mounts and lift the car and check the exhaust properly. I don't like the way this noise has suddenly appeared out of the blue.
CRAIGO is offline   Reply With Quote
Old 09-29-2010, 09:28 AM   #5
Junior Member
iTrader: (4)
 
Join Date: Sep 2010
Location: Australia
Posts: 168
Total Cats: 10
Default

Freakin heck, just watched the video... that isn't piston slap. Sheez!

So you have an early NB... have you had the #4 thrust bearing checked? Probably would have happened early in the car's life so this probably isn't the problem but you should check it anyway.

You might have a valve sticking open, but ours is a non-interference engine so this probably wouldn't be causing the noise on its own.

Whatever it is sounds BAD. When you figure it out i'd love to know what it is.

Last edited by zossy1; 09-29-2010 at 12:23 PM.
zossy1 is offline   Reply With Quote
Old 09-29-2010, 10:12 AM   #6
Senior Member
 
Join Date: Mar 2006
Location: Schwarzenberg, Germany
Posts: 1,497
Total Cats: 81
Default

Have a look at your exhaust, it could be knocking to the chassis somewhere - I had something like this once. Sounded like that!
It just knocks at startup because the engine is moving quite a bit at this ...
Zaphod is offline   Reply With Quote
Old 09-29-2010, 05:43 PM   #7
Junior Member
Thread Starter
 
Join Date: Oct 2008
Location: Manchester, UK
Posts: 274
Total Cats: 0
Default

Well I've found the source of the problem. It's nothing serious Phew!

One of the intercooler mounts had sheared on the outlet side. This caused the intercooler and intake tract to become a little loose around the throttle body inlet and allowed my blow off valve silicone tee to wobble enough under cranking which caused it to hit the underside of the bonnet.

Broken intercooler bolt.
Name:  280920101258.jpg
Views: 79
Size:  112.0 KB
It's pulled itself out of the body, probably through stress (and I didn't rivet the TDR plates to the stock welded nuts in order to strengthen them )
Name:  280920101259.jpg
Views: 78
Size:  96.4 KB
Name:  280920101260.jpg
Views: 79
Size:  102.8 KB

I've temporarily fitted a suspended steel cable to hold up the intercooler on the outlet side until I can source some suitable fixtures to perma-mount it.
Name:  280920101261.jpg
Views: 78
Size:  134.0 KB

I also rotated the BOV and tee from here:
Name:  290920101262.jpg
Views: 80
Size:  114.4 KB

To Here:
Name:  290920101265.jpg
Views: 80
Size:  145.4 KB

No more noises!
The cold start vs. hot start was a red herring. Thinking back, I've realised I only ever cold started the car with the bonnet shut. When trying hot starts I was always in my garage with the bonnet propped open trying to find the source of the knock.

Thanks for all the suggestions guys.
CRAIGO is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
Buzzing from driver side of engine bay? (MS3 install) nick470 MEGAsquirt 7 06-16-2017 02:53 PM
Hey everyone another n00b here Big_gumby Meet and Greet 80 10-05-2015 05:06 PM
Expected intake temps on the track? tazswing Race Prep 20 10-03-2015 12:04 PM
Leaky Wilwoods mx592 Suspension, Brakes, Drivetrain 1 10-01-2015 01:45 AM
Low oil pressure after 1.8 swap and new turbo setup JesseTheNoob DIY Turbo Discussion 15 09-30-2015 03:44 PM


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 10:49 PM.