May have rod knock....

[89nasupra]

Was not sure which section to put this so please move if need be.


I believe my car has rod knock. Since I got it running in March and driving it back and fourth to work everyday I have only put 4000 miles on it. What I think is rod knock may not be. I read the write up that Mike (supracentral) did in the engine internals and I will check some of that this weekend. Those that don’t know me I was a mechanic for 15 years professionally in a shop so I know my way around a engine. Now, the knock comes and goes it’s not a constant knock like when my GE got rod knock. It says in the write up that rod knock is better heard above 2500 RPM but it gets quieter if not gone when I get above that RPM. Also if the engine has a load on it, it’s even quieter than just idling or says idling through a parking lot in gear. I’m going to get the stethoscope and take all the belts off this weekend and check it and start killing spark plugs to see if I notice a difference in the noise at all.

What do you guys think?

 

[GrimJack]

Check all the other likely culprits... loose front main damper pulley bolt, loose flywheel / flexplate, and accessories that run off the belts.

 

[7Matt-GE]

are you auto?

 

[89nasupra]

Grim, only thing belt driven is the water pump and alt. I have removed the power steering and A/C from the car. I also have solid motor mounts which I forgot to mention. Some back ground on the engine, bought a running donor car for my turbo swap that had "rod knock" turned out to be a broken turbo shaft in the exhaust housing. I tore it down anyway just to check the condition and everything looked fine no scaring or scratches on the rod or main bearings so I torqued everything back down and put it in the car. i'll get under it this weekend with it running and see if i see anything that may be hitting something causing the noise.

Matt, yes I'm auto.

Could the cams being out of spec on valve clearance cause it to sound like rod knock?

 

[GrimJack]

Could the cams being out of spec on valve clearance cause it to sound like rod knock?

Absolutely. Pretty easy to check, too, just need to pull the valve covers and run a feeler gauge between the cams and shims.

Auto make the loose flexplate likely. It's one of the things that sounds exactly like RK, and it's caused quite a few false alarms.

 

[89nasupra]

Loose flex plate as to the crank or the converter? Would loading the engine i.e. in gear stopped or accelerating cause it to quiet down a good bit?

Had an Isuzu pickup years ago that i had to adjust the valves on. it was more of a clicking noise than a knock. Different valve train design would change the pitch of the sound?

 

[GrimJack]

I'm afraid I don't know the details on the flex plate, all mine have been 5 speed cars. However, having been here for a long time, I've seen the loose flexplate culprit pop up reasonably regularly over the years.

As for the valvetrain, yes, this is a shim over bucket head and it doesn't sound like other engines with loose valve clearance. Even my older Mk2 Supras didn't sound like these ones do, a loose valve was easy to distinguish on the 5M, while on the 7M it's not hard to get them confused at all.

 

[89nasupra]

Thanks Grim, I'll do some checking on this over the weekend and post my findings. Got me feeling a little better thinking it's not rod knock. My oil is clean and there are no metalic shavings in the oil so it was trying to figure out what it could be. Anyway, thanks again Grim.

 

[7Matt-GE]

ok i will tell you right now im 90% confident its your drive plate. either its cracked or the bolts are finally giving out. my auto does the SAME exact thing. infact, i thought it was rod knock till i went over to my dads and physically inspected it with him. sure as shit it was the drive plate the bolts were comin loose.


happens to a lot of autos. replace that drive plate and replace those bolts

 

[89nasupra]

I have noticed it has gotten louder over the past week or so and i ran the shit out of it a few times a few weeks ago racing one of my friends on the back roads here with some heavy loading it up on the line to try ot get a good start on him. And not that i think of it, we had the same thing happen to my dads car but he sheared the bolts and badly damaged the flex plate. Can you see this form taking the inspection or starter out?

 

[gsxr141]

i think i have the same noise. the symptoms are the same. if i figure it out i'll let you know what i find.

 

[7Matt-GE]

I have noticed it has gotten louder over the past week or so and i ran the shit out of it a few times a few weeks ago racing one of my friends on the back roads here with some heavy loading it up on the line to try ot get a good start on him. And not that i think of it, we had the same thing happen to my dads car but he sheared the bolts and badly damaged the flex plate. Can you see this form taking the inspection or starter out?

i honestly don't think so though if you get up next to it youll definitely hear where it's coming from.

TICKATICKA TICKA TICKA TICKA TICKA

 

[89nasupra]

Well either way the engine and or tranny will have to come out. I'll pull the tranny and see if the flex plate is cracked or damaged in any way and if not I'll be right there so I can just pull the engine and see how the rod bearings look and check clearance.

 

[grimreaper]

any out of spec vavles I have ever had started ticking or making racket right at idle and never stopped until the engine noise drowned it out. the tick is also half speed. At lower rpms you can almost count each time that bucket and shim get hit by the cam. Also always sounded like it was right in front of my dash, or even in the dash. good luck

 

[vabeachsupra]

On the edge of my seat !!!! Having the same problem with my 91 auto, would like to know the outcome.

 

[Backlash2032]

I believe that the valvetrain design on 7Ms can replicate rod knock like sounds. My car has nearly the exact same issue. Theres a heavy knock when i first start it after it sitting for a day or so, and then it quiets down after oil gets circulated. Its been like this since ive gotten the car, and ive put 7000 or so miles on it, and some of those miles were pretty damn hard. Ive hit the rev limiter multiple times (mostly until I got used to having a limited slip. So tail happy lol) ive accidentally revved the nuts off of it by downshifting into 2nd when it was cold. and just have done things that if it did have that loose of clearances in the bottom end, im pretty sure it would have blown by now.