Engine Knock

Donovan · Post by **Donovan** » Mon Jul 23, 2012 3:03 pm

My Brother is looking again at another MX5, this time a NB turbo. The description of it is as below, no mention of a cert, plus there is the comment on the last line. I am trying to find out who did the engine rebuild, as in theory it would be covered by the Consumer's Guarantee Act if it was rebuilt and then spat a piston, or did a big end a couple of months later.

Any clues to what the knock might be, he doesn't say whether it is a constant knock, or only at big revs knock.

Engine; Factory BP 1839cc engine fitted with an HKS turbo kit comprising of HKS V-CON engine management, Garratt turbo charger and front mount intercooler.

Gearbox; Factory 6 Speed manual with an o s Olsen super single clutch.

Brakes; Factory 4 wheel discs with large 4 pot calipers on the front.

Suspension; Factory double wishbones on each corner with height adjustable coil overs. (Front currently have standard shocks fitted but come with adjustable platforms to be fitted)

Body; lovely black paint with very few km's on it. Also has a very low km soft top. Type N front bumper.

Interior; limited edition mazdaspeed red seats with a mazdaspeed rollbar.

Disclaimer, the engine was rebuilt a couple of months ago and has developed a knock.

Stevo · Post by **Stevo** » Mon Jul 23, 2012 5:07 pm

Yeah, I saw that one as well and was wondering about it to. If it was done professionally, I think the CGA would only cover the person that paid for it. Not the next owner. But i could be wrong.
Stevo

Donovan · Post by **Donovan** » Mon Jul 23, 2012 5:30 pm

Not 100% sure about the CGA for such a short time frame, but either way, makes me suspect that it wasn't professionally done, otherwise the guy that has it at the moment would be getting it fixed under the CGA rather than selling it (either that or he just doesn't know his rights), but even the lameman should know there would be at least a 90day warranty on mechanical work.

WideOpenThrottle · Post by **WideOpenThrottle** » Mon Jul 23, 2012 5:57 pm

Might be something easy like a worn/loose engine mount [but i doubt it]!
More like engine internals.

SLYDIT · Post by **SLYDIT** » Mon Jul 23, 2012 7:27 pm

pretty simple really.
the description says it all.
the car is fitted with an FconV ecu which are CRAP (well actually the availability of tuners is crap). the car probably had its boost wound up and it detonated and so required a rebuild. but because no retune was done, the rebuilt engine died too.

youd need to replace the engine with another 1800 then get a better ecu that you can actually tune. then youd be set.
either that or rip off the turbo altogether and sell it. then the money you get from the turbo gear would pay for the replacement engine.
I would also want to check EXACTLY which ecu it had I.E if it actually was a F CON V or something else

punkoutnz · Post by **punkoutnz** » Mon Jul 23, 2012 8:00 pm

Yeah I had a mate that jumped up and down when his new engine ran a bearing in under 1000kms and tried pointing it at the builder. But when I questioned him about it he hadn't followed the guys advice (which was drive it gently for a thousand kms). He had run 20psi through it from the first time he started it. Yup... That'll do it!

It's not always the engine builder's fault.

Donovan · Post by **Donovan** » Mon Jul 23, 2012 8:33 pm

Well, turns out it's all a bit academic anyway, he rebuilt the motor himself, see response below.

"I rebuilt the engine after the head gasket failed because the previous owner hadn't used coolant. I had the head plained, fitted a new gasket set, new rings and big end bearings as well as new water pump, cambelt etc. After a short time the engine developed a knock. A friend said it sounded like a spun bearing"

Angreal · Post by **Angreal** » Mon Jul 23, 2012 8:40 pm

These "knock" sensors that people have mentioned every now and then, are they easy to retrofit into a car? Seeing as I'm new to this whole forced induction game, are they necessary for a supercharger setup?

Speaking of retrofitting other things in and kind of related to knocking, a wideband sensor, again is it necessary? Does it replace the existing sensor that sits right before the cat?

I have realised that I know very little about forced induction other than the mechanisms on how it all works

Euen · Post by **Euen** » Mon Jul 23, 2012 9:09 pm

Knock sensor is like a microphone attached to the block which provides info to the computer so that the timing (and or fuel) can be adjusted at the slightest hint of detonation. The NBs came with one fitted but not the NAs. You would need an aftermarket ECU to fit one.

Once again, a WB o2 sensor is only any good to you if you can adjust your fuel mixture which is not possible on the standard ecu. Some piggy-backs will allow adjustment though.

Donovan · Post by **Donovan** » Tue Jul 24, 2012 9:51 am

If it is a spun bearing, and ideas of what is involved cost wise to fix, the guy said oil pressure was ok, and he shut the engine down as soon as the noise started, and had it towed back, so chances are that the damage could be minimal?

punkoutnz · Post by **punkoutnz** » Tue Jul 24, 2012 10:00 am

Really it's hard to say without having a look.
First you wanna see if it's picked up on the crank, if it hasn't then it'll just be a case of replacing that bearing (making sure you get the right grade, which is possibly why it ran the bearing in the first place if it wasn't running the right clearances).
If it has picked up on the crank, then you will either need to get the crank machined or replaced depending on how bad the marking is.

You also wanna figure out why it's run the bearing so quickly before you go putting it all together, but I would hazard a guess by saying it was either not run in properly (probably thrashed from the moment he turned the key) or the wrong bearing was installed.

Euen · Post by **Euen** » Tue Jul 24, 2012 10:06 am

As Punk' says, it is going to depend on how much damage there is. The cranks are forged so are pretty strong but that doesn't mean that it may not require grinding. The early NBs had a problem with crankshaft thrust bearings as well and the owner may not have noticed that when he rebuilt it.

I picked up a damaged NB engine a few years ago which had run bearings and the crank looks fine but I have not had it inspected professionally or properly mic'd up yet.

The cheapest outcome will be a full set of bearings and a gasket set. Given that this is the second time that it has suffered, I would want to totally strip the engine and flush out all the oil galleries to ensure there is no residual crap in there.

Have a talk to John or Scott at Glendene Engine Reconditioners. they may be able to give you an idea.

Engine Knock

Engine Knock

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