[Supras] mystery knock

Thu Apr 19 19:04:21 CDT 2007

Interestingly enough I checked valve clearance a couple of days ago during the valve cover gasket replacement (getting too contain oil inside the crankcase after merely a year) with Fel-Pro instead of whatever that cheap gasket was.
It's interesting you mentioned the turbo as a possible source as I didn't hear the noise until the recent turbo rebuild with upgrade to 57 trim in January. I didn't hear the noise until a few weeks after the install of the turbo which pulls a whole bunch harder at higher rpm's which has subsequently influenced my higher rpm shifts on frequent occasion ;)
If there is a chipped blade it must be on the exhaust side as I took advantage of the opportunity to examine the intake side while the accordion hose was off. I'm thinking a chipped blade would likely be consistent instead of only discernible before the engine reaches operating temperature.
It won't hurt to look at the exhaust side next time the downpipe is off though.

Thanks,
Rockey 91T

Harley <CoolGuyHB at socal.rr.com> wrote: don't know if this has been covered yet... did you check the turbo to see if 
you might have chipped a blade, or if the turbine is loose? Mine ticks at 
around 3500 rpms because of my warn camshaft. Warn shims would make the same 
sound. Also... you said that you rebuilt the motor... have you had the 
valves re-adjusted?

Hope this helps...

- Harley(87t)
----- Original Message ----- 
From: "Rockey Fox" 
To: "Jeff Mohler" 
Cc: ; 
Sent: Thursday, April 19, 2007 6:43 AM
Subject: Re: [Supras] mystery knock

>I tried it out this morning and the mild knock was not discernible except 
>when the engine is under load and boosting. It was only about 45 degrees f 
>outside this morning.
>
> ----- Original Message ----
> From: Rockey Fox 
> To: Jeff Mohler 
> Cc: berniek at technicaldevelop.com; supras at supras.com
> Sent: Wednesday, April 18, 2007 10:01:08 AM
> Subject: Re: [Supras] mystery knock
>
> It's not really a hammering, more like a mild knock. That one instance was 
> the only time I ever experienced that aggressive knock that seemed to be 
> hammering. I'll try the hold at 3k rpm when cold in the next couple of 
> days. The car lives in the garage usually but I have had to park it 
> outside a few times over the past several weeks which was when I really 
> noticed it. Seems to be worse at colder temps.
>
> ----- Original Message ----
> From: Jeff Mohler 
> To: Rockey Fox 
> Cc: berniek at technicaldevelop.com; supras at supras.com
> Sent: Tuesday, April 17, 2007 9:25:37 PM
> Subject: Re:
> [Supras] mystery knock
>
> That knock at startup worries me tho.
>
> Your clearances after a rebuild should be tight enough that the leftover 
> oil film should have enough cushion to prevent the hammering.
>
> If when cold in the driveway at startup..if you rev to like 3k and hold it 
> there..does it hammer?
>
>
> On 4/17/07, Rockey Fox  wrote:
> I've had only one episode where the knock was alarming right after
> startup and it diminished rapidly after oil pressure built up. That was
> a week or so ago and hasn't recurred. I've been running Pennzoil full
>
> synthetic since the second oil change (1st at 100 miles, second at 3000
> miles) after initial break in. I'm guessing I've put about 25k miles on
> since the rebuild and the synthetic oil and filter is changed
>
> religiously at 5000 mile intervals. It takes 6 quarts to fill due to
> the oil filter relocation kit and the larger Ford oil filter.
>
> I'll keep up with it and let the list know of any further developments, 
> hopefully it's as Jeff predicted that something, probably a piston, is 
> slightly smaller than it should be when cold. That being the case I should 
> be able to continue driving without major failure for quite a few more 
> miles.
>
>
> Thanks for sharing your thoughts,
> Rockey 91T
>
> ----- Original Message ----
> From: "berniek at technicaldevelop.com" <
> berniek at technicaldevelop.com>
> To: supras at supras.com; Rockey Fox 
> Sent: Monday, April 16, 2007 9:19:50 PM
>
> Subject: Re: mystery knock
>
> Dear Rocky and group:
>
>    The knock problem may be a variant on a phenomenon I noticed before my
> '90T blew the head gasket at 156K miles (have not yet finished rebuilding 
> a
>
> JDM core after 18 months).
>
>    I had noticed piston slap for quite a number of miles before warmup,
> which as in your case was when the engine was cold.  One surprising 
> element
> was that I had used synthetic oil since the car had about 38K miles on the
>
> odometer, so wear should not have been a factor, especially considering 
> the
> oil jets used in turbo engines.  .
>
>    I never went in to boost until full warmup, but I can tell you that 
> with
> light throttle loading when cold, the sound changed in vowel character, 
> from
>
> "oooh" to "aaah" as throttle opening was changed.  It almost sounded like
> subdued diesel clatter except for the vowel character change.
>
>    Another surprising characteristic that works against noise production 
> is
>
> the stock pistons:  They are autothermic (the have cast-in steel struts
> under the wrist pins to control expansion for noise control when cold). 
> Yet
> another surprising factor is that stock pistons have wrist pin offset to
>
> load the major thrust side of the skirt, which JE and maybe other forged
> pistons do not.  The offset was for noise control.  In American cars of 
> the
> 60's and such, it was usually 1/16" toward the major thrust side.
>
>
>    Yet, the sound (it could not really be described as a noise) 
> disappeared
> as the engine warmed up.  You might want to listen carefully under light
> load conditions as the engine warms up.  I'm curious to know what you 
> find.
>
>
>        BernieK
>
>
>
>
>
>
>
>
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