ncj

Just had a complete rebuild of a 2.5 with omega forged pistons and manley con rods,etc etc. But just how noisy should these motors be? The general opinion seems to be noisy till warmed up, then almost as quiet as standard.
Mine 'taps/ knocks' only on load or acceleration. The guy who built the engine says that it sounds like piston slap,he fitted the pistons with a 3 thou clearance, is this about correct? He then suggested a 10/60 oil which made it even worse, and knocks under load even when hot, albeit not so loud. He has given me a years warranty so not too worried, but would be good to hear any thoughts.

ditchmyster

iTrader: (7)

Who built it? pm me if you don't want to say openly.

Steve Whitehorn

iTrader: (13)

Different pistons have different expansion properties.
Omegas are very good pistons. However they expand quite a bit from cold. So need more clearance. They tend to be noisy they also can let oil past the bores when cold too.

My Omega pistoned 2.5 was noisy and used oil. But it was good engine that made good power.

the shreksta

iTrader: (20)

When you say taps/knocks do you mean it's sounds clackety? My forged 2.5 with mahle pistons sounds like a sewing machine from cold with the slightest puff of blue smoke if left for a week or so but when warm it's not quiet but not as loud as from cold.never had to top the oil up and doesn't smoke at all on boost/tick over etc

Take it to a specialist for an opinion

poolio74

Pm me if he tells you who built it

ncj

Yes i guess thats the best bet. It sounds as though you have a good engine there. Yes clackety but only under load otherwise very sweet and quiet.

ditchmyster

iTrader: (7)

You'll get nowt from me I'm old school, you can pull my finger nails out and I wouldn't tell.

poolio74

Your no fun

wms-racing

Omega pistons don't have any gudgeon pin offset, this makes them noisy compared to a Mahle type which is designed with pin offset. They are more of a race spec design with very short piston skirts as well. A great high performance piston but I wouldn't use them in a day to day car myself.

ncj

Ah ok, i didnt know that, orthough im not sure what gudgeon pin offset is [lol[ So your reason for not using them day to day is that they are too noisy? The car is about 480 bhp so maybe it needed this sort of piston.?

mickeymouse

So here is the problem.... How noisey is noisey??

I've also got a forged 2.5.. And mine is also noisey.. But is it more so than say, to yours??

I believe these engines (boxer) are generally noisey anyway.. So it's unfair to compare it to a 'normal' car. I've watched videos and read and asked on here before.. And I'm still no closer to the answer. But the general thought was.. Yes it's normal for them to be noisey.

It is very unnerving but I've been assured it's ok and normal and running fine.

Try to compare it live with another 2.5 both forged and standard.

ncj

Yes, i have tried to find another forged 2.5 to listen to. But i do get this noise when its fully warmed up, and if it is a bit of piston slap, what damage is that doing to the bores, ive just had a brand new block ! The old block was too far gone [oval bores] to re use because of piston slap.!So you can see why im wary.

mickeymouse

I totally agree.. I worry that mine is going to drop its guts every time I put me foot down..!!! You sure it's not one of the idlers or tensioner?? Have a look on YouTube.. Was a good one for what seems like piston slap but was the tensioner bearing.

ncj

no im not sure, so yes, good idea will have a look on you tube.

mickeymouse

was on the pad earlier and linking youtube vids is a real bitch!!





the 2nd one gives you an idea of what the idlers sound like.

mickeymouse

ahh!! first vid skip to 4 mins 28 secs

ncj

Ok looked at both vids, in the second vid did i get it right that the timing belt tensioner is hydraulic and relies on engine oil pressure or is it just a sealed hydraulic system that can leak out?

ditchmyster

iTrader: (7)

I know who built this engine and he's got nothing to worry about

I understand why you're nervous having had a couple of engines let go myself, it's very un-nerving.

Your engine builder came and had a listen and said it's fine, I'd listen to him, he knows what he's talking about and your warranty is good with him, he will honour it, the fact he came to listen to it tells you that, if there was something wrong with it he'd have wanted you to stop driving it because he's the one that will have to pay for it and fix it.

Just enjoy it.

wms-racing

The pin offset is so the internal force on the piston pushes slightly to one side (thrust side) this stops the pistons from wobbling (technical term, lol)
Ive recntly built a 2.5 with some cp pistons which have no offset, it is noisy at low revs. It's just the nature of them, I prefer to use Mahle's in most road car builds for the very reason this post was started. The less noise an engine makes the happier the Customer, in most cases.
There isn't any significant performance advantage/disadvantage in a road car setup.

Steve Whitehorn

iTrader: (13)

+1
Mahle would be my piston of choice in a road car.
The quietest forged engine I have had had Mahles in it

mickeymouse

Now that is reassuring to hear