Tchaps

Hello everyone, first time poster here from the UK.

Hoping for a bit of a help with an issue on an engine I recently built.

Specs are:
Supertech 84mm 9:1 pistons.
Manley Rods
Balanced and polished crank (still within standard tolerances, checked for round etc.)
New bearings, tolerances checked
It is a shim under bucket cylinder head with custom cams.
M45 Supercharged for now...

Engine runs and pulls great, no odd noises at idle, or on throttle. Done about 3-4000miles on it and a trackday. Hardly any oil has been used, no smoke, no temp issues, nothing to suggest it is anything but a completely healthy engine. Apart from what I can only describe as a sharp rattle between 2500 - 4000rpms only at very light / cruising throttle openings. This noise has been consistent since the install.

The noise has:
> Stayed the same consistent volume, in the same rev range at the same throttle openings. Same volume (and frequency i think) through that 2500 - 4000rpm range ever since the build.
> Always happens when going through the 2500-4000rpm light throttle range.
> Does not vary with engine temp.
> I cannot replicate it stationary revving the engine, it is not audible with the car idling.

I initially thought it was my old exhaust - changed entire exhaust, no change. Thought it was my SC set up, found a crack in a weld, repaired it, no change. Checked all heat shields, all bolts anything that I would have touched while doing the engine, no change. Really at the end of options with the noise coming from things external to the engine.

It doesn't effect the performance, but I have spent a lot of money on this so I really would like to not have this annoying rattle!

My thoughts initially on internal issues were a very slight rod knock, but everything was measured and in spec, plus I would think any rod knock would get worse and worse and certainly not survive a trackday?

Possibly a resonance in the valve train? It is shimmed to spec though.

Piston wrist pin slap? Can't really see why this would occur on a new engine? I assembly lubed everything, primed oil pump and turned engine over until full oil pressure was reached before first start up. Supertech pistons + Manley rods appear to be a well used combo on here without issues.

I have had an endoscope down the bores, no obvious sign of piston slap. Poked the pistons with a screwdriver (technical I know) and there is no play that I can feel on the cylinders.

I am going to take the engine out and inspect the internals in a couple of weeks anyway, but looking for suggestions from you helpful people to see if there are any other bits I should check out.

P.S. I know I didn't need to forge the engine for an M45 blower. My last engine used about a litre and a half of oil a session, so needed a rebuild, and I have plans....

Anyway, any ideas welcome.

Tom

add lightness

Flywheel rattle? Are you running a new setup or something you're familiar with?

I have two different aluminum ones that both rattle - the 1.6 Fidanza has a metallic rattle at ~3k cruise and light accel like you described, and the-old school FM rattles at idle.

Savington

iTrader: (31)

Almost certainly not an internal issue. With 3k+ miles on the bottom end, any rattles which were there at the start would have 100% destroyed the motor by now if they were of a mind to do so. You're looking for an external resonance.

Tchaps

Thanks, flywheel / clutch combo is a known quantity from before the engine. Not to say it couldn't be causing it now, it all had to come apart for the build, but I tend to be careful about torques with heavy metal spinning disks next to my legs. The flywheel isn't an ali one with a separate friction disk, just a bogo standard 1.8 one. Got myself a nice shiny light one (still steel) for when I pull this engine out again though.

On internal issues, that was my thinking really. If it was serious it would have destroyed itself, or atleast get worse, particularly with track abuse. There is a lot of custom fab work around the engine, quite a bit that has changed with the new engine, so a whole myriad of potential causes that have escaped me so far. Fingers crossed it is something to do with that.

Been really concentrating on the noise while driving. It definitely sounds light, rather than a heavy bottom end thump.

Thanks for the suggestions / comments, I'll keep you all posted when I pull it out. Any more suggestions gladly received.

Tom

sixshooter

iTrader: (12)

You might try getting some electronic det cans and mount the microphone in different locations and listen to it while cruising. It may help you narrow down the location of origination.

SamM_UK

Are all your exhaust bolts secure?

I had a very similar rattle on an old car which turned out to be an exhaust bolt that'd lost it's nut and was rattling at 2500-3500rpm. It was the at the join between the downpipe and centre section. Also thought the bottom end had shat itself until I found it!

Godless Commie

iTrader: (2)

Please remove your SC belt and give it a go.
Chances are the noise will change or disappear altogether.

I had a similar issue with my MP62, and all I had to do was replace and adjust the rubber tensioner below the charger.

miataman04

iTrader: (1)

That could be a lot of things. Post a video if you can. That will help a lot.

richbobby

TLDR: OP never got rid of the noise. Most likely some trait of the supertech pistons. I have the same exact symptoms as listed above, with a very similar setup.

I PM'ed TChaps to see if there was any development, here is the correspondence (ok'ed by chaps to post)



Wanted to update JIC other folks out there have this setup and issue. I haven't torn my engine down yet to see if anything is amiss, might just live with it and hoard parts for another engine build when the time comes.