Rattling from engine bay at v high rpm (6000rpm)

Engines, Transmissions & Final Drive questions and answers

Moderators: timk, Stu, zombie, Andrew, The American, Lokiel, -alex, miata, StanTheMan, greenMachine, ManiacLachy, Daffy

User avatar
hamx5ter
Racing Driver
Posts: 903
Joined: Sun Sep 20, 2009 8:39 am
Vehicle: NB8A
Location: Cherrybrook, Sydney

Rattling from engine bay at v high rpm (6000rpm)

Postby hamx5ter » Sun Dec 27, 2015 7:54 pm

I wasn't too sure where to post this issue... luckily, 'Engine, transmission & final drive' seems about right :lol:

Last time out at SMPS I noticed some rattling coming down the hill towards the 180 deg turn. At this point, I was basically on redline on 3rd, because I didn't feel like changing up to 4th just to change back again.. (new track). I was somewhere between 6500-6800 rpm for a while and had plenty of time to note the rattling.

Apart from the rattling at 6500 though, the car starts, runs well, etc.. perhaps uses a little oil, but I can't tell with limited use. Exhaust is clean, no smoke, etc. It does like to snap crackle and pop on over run if that's any extra info. Engine sounds / runs great (if a little agricultural) at all other revs.

Wasn't too sure what to make of it, so took it to Mania for David to have a look at. it didn't seem to rattle when we revved it, but I didn't rev it to 6+ as it wasn't really warm enough.

Took the car down old pac and the fwy yesterday so I could have a proper listen through different gears, and found that the rattling happens on both 2 and 3 at rpm past 6000ish. Obviously, I couldn't redline it on 4th, but I assume it would be the same. I popped it neutral while it was running and revved and rattling comes on, again at 6000+ rpm. I forgot to try the same thing with the clutch in.

I won't get a chance to take it to mania before end Jan, as we will both be away, so hoping I can get a handle on this prior.

Any ideas? I really don't want this engine to go boom. Hamx5ter will be left by himself in his hutch as I cannot really afford another heart transplant.

Deen
Image

User avatar
NitroDann
Forum sponsor
Posts: 10280
Joined: Thu Nov 05, 2009 12:10 pm
Vehicle: NA6
Location: Newcastle NSW
Contact:

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby NitroDann » Sun Dec 27, 2015 7:59 pm

This is the kind of thing that chassis dynos are made for.
http://www.NitroDann.com

speed wrote:If I was to do it again, I wouldn't even consider the supercharger.

User avatar
hamx5ter
Racing Driver
Posts: 903
Joined: Sun Sep 20, 2009 8:39 am
Vehicle: NB8A
Location: Cherrybrook, Sydney

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby hamx5ter » Sun Dec 27, 2015 8:13 pm

Sure, dyno would help, but I was hoping there would be a checklist I could tick off prior.. Perhaps things I could check visually to eliminate the usual suspects.
Image

User avatar
zossy1
Racing Driver
Posts: 1979
Joined: Wed Aug 18, 2010 8:48 am
Vehicle: NA8
Location: Southern Highlands, NSW
Contact:

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby zossy1 » Mon Dec 28, 2015 12:10 pm

Hi Deen,

A rattling noise could be anything - broken valve Spring (inducing valve float), engine ping / detonation (bad fuel?), idler bearing, loose timing belt tensioner, or anything harmonic (like a loose bolt somewhere).

It could be bottom end, but I doubt it.

I'd be giving the engine a careful once over, starting with cylinder leakage and compression tests, bore scope, and then pop the valve cover off and check the valve gear. If that all comes up trumps, go over every nut and bolt attached to the engine, from the engine mounts upwards.

User avatar
Okibi
Speed Racer
Posts: 10898
Joined: Thu Aug 21, 2003 11:00 am
Vehicle: NB SE
Location: Perth, Western Australia
Contact:

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby Okibi » Mon Dec 28, 2015 1:34 pm

Could also be a dead cat, exhaust baffle, heat shield, engine leaning out?

Have you done preventative maintenance to narrow it down like changed oil, fuel filter, decent fuel in the tank, looked for anything loose?
If you had access to a car like this, would you take it back right away? Neither would I.

User avatar
hamx5ter
Racing Driver
Posts: 903
Joined: Sun Sep 20, 2009 8:39 am
Vehicle: NB8A
Location: Cherrybrook, Sydney

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby hamx5ter » Mon Dec 28, 2015 2:32 pm

Thanks Dave.. The cat and muffler is new, cat replaced only a few months ago, muffler last year.

Fuel is usually 98. I have put in 95 here and there but almost always 98. I fuel up at a pretty busy Caltex so I am presuming the fuel would be good. Also, outside of that 6k+ rpm, the car runs really well, so I would bad fuel would show up at other rpms too. It was serviced just recently and Mania tend to tighten things up then, so I don't think it would the normal things that work themselves loose. Could be everything else though :D

Hey Chris, much internet surfing :( also brought me to idler / tensioner (didn't know they were two different things!), and valve float. I'll go have a look at the tensioner / idler for play, and try check the heat-shield, but I think looking at the cylinder compression / leakage, etc. is a bit beyond my capabilities I might have to leave it to Mania to have a look at the engine itself when they re-open.

Hope it can be sorted out before our Drifto day end Jan.. :frown:
Image

User avatar
hamx5ter
Racing Driver
Posts: 903
Joined: Sun Sep 20, 2009 8:39 am
Vehicle: NB8A
Location: Cherrybrook, Sydney

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby hamx5ter » Mon Dec 28, 2015 3:13 pm

had a look at the belt / pulley... gee with no a/c & p/s, the path is very clear.. also, engine mounts were replaced (with SE mounts) when the engine was dropped in at the start of the year..

but looking at the back of the engine, where it connects to the transmission.. should I really be missing a bolt here? :shock:

and where's my undertray?
You do not have the required permissions to view the files attached to this post.
Image

User avatar
hamx5ter
Racing Driver
Posts: 903
Joined: Sun Sep 20, 2009 8:39 am
Vehicle: NB8A
Location: Cherrybrook, Sydney

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby hamx5ter » Mon Dec 28, 2015 4:17 pm

so apart from that bolt...

look at the clearance between the header and that flange... maybe 1.5mm? is that a bit too close? I don't think it's worn though..

edit 28/12/2015 16:22:16 texted David / Mania and he thinks it might be something to do with the exhaust. We'll pop it up on the hoist when they come back, and should be able to track it down. He doesn't seem to think it's engine-ka-boom, so I'm hopefully... :lol:
You do not have the required permissions to view the files attached to this post.
Image

User avatar
hamx5ter
Racing Driver
Posts: 903
Joined: Sun Sep 20, 2009 8:39 am
Vehicle: NB8A
Location: Cherrybrook, Sydney

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby hamx5ter » Sat Jan 30, 2016 11:27 am

Just to finish this off.

Took it to Mania yesterday and put it up on the hoist.
Revving to redline in neutral or in gear, and no rattling from the engine. So at least hopefully no engine-ka-boom on Sunday.

Before we put it on the road, I asked for a closer at the crazily low clearance between my headers and the engine block, but David that it would be fine. The BRAKE LINE though was very close to the headers and there were some small marks on them where it must have been rubbing.

David bent it back a little bit and we took it for a spin. Revved to 6-7k and no more rattling. Will find out tomorrow :)
Image

User avatar
zossy1
Racing Driver
Posts: 1979
Joined: Wed Aug 18, 2010 8:48 am
Vehicle: NA8
Location: Southern Highlands, NSW
Contact:

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby zossy1 » Sat Jan 30, 2016 1:11 pm

Happy days! Hopefully it's all good :)

User avatar
hamx5ter
Racing Driver
Posts: 903
Joined: Sun Sep 20, 2009 8:39 am
Vehicle: NB8A
Location: Cherrybrook, Sydney

Re: Rattling from engine bay at v high rpm (6000rpm)

Postby hamx5ter » Sat Jan 30, 2016 9:10 pm

Will find out tomorrow! :D
Image


Return to “MX5 Engines, Transmission & Final Drive”

Who is online

Users browsing this forum: No registered users and 67 guests