[Mk2] [Turbo] Slight rattle on new build engine?

[mazzerdod]

Again I think I may or may not have an issue if you have read my previous topic I have just completed a ST205 engine build using forged JE pistons.

Now the cars been started everything seems fine its done 20miles not exceeding 2.5k rpm and no boost.

I've since dropped the oil and filter for fresh but I have noticed a very slight rattle from the motor when you just pick the revs up a little off of tick over it does concern me a little but it has had new everything little ends, bigends etc do you think the forged pistons could be the problem?

I have read that some people have noticed a little piston slap when running forged pistons?

I thought it might be because everything isn't run in yet?

The machining, measuring, and assembly of the pistons, rings, rods and crank into the block have all been done by a local engineers whom are repetable, they built engines for me in the past and all the local garages use them.

What I'm trying to say is I can't believe it could be bottom end i.e. bigend bearings but it does sound like it to me.

Any ideas?

[^Trickster^]

To find out if its the bottom end just pull one spark plug lead at a time, the noise will subside if its rod knock as you will take the load off that cylinder due to it not firing.

You could have piston slap but it would of been noticable the first time you started the engine, really if its machined properly you should not get piston slap but some people do get it, ive had it and people seem to just say its normal but i think thats only because you spend all that money and want to ignore it as a problem! It could be this that your hearing.

2.5k and no boost is not the way I would be running a new engine in tho to be honest. The thing that seats piston rings into the cylinder walls is cylinder pressure forcing the rings out. I would idle the car for its initial run in on cheap oil and change the oil and filter, then i would drive it for 50 miles up to 5krpm with plenty off rev changes, alot of people will accelerate with partial throttle and some boost say 5-10psi to 50mph or so then let the engine decelearate down again.

You dont want constant revs, you want the engine to see as much variation as possible.

Your only running the rings in anyway, best way is on the dyno so you can tune it and give it full throttle.

Graeme

[mazzerdod]

Hi it was noticable from the first start its only very slight.

I've read that the toleances between the forged piston and the bore are greater than those of cast pistons because the forged pistons can expand upto 12% more?

[JJ]

When you first crank it, keep an eye on the oil light....does it stay on when the engines got that slight rattle ??!

Is it always there ??

Try not to abuse it ....

Ocassionally what can happen, you may have new components through out, but if the block has some swarf in it from the machining, and it hasn't been cleaned / flushed properly, on first start up the oil can drive this swarf into the bearing where it can perish it very quickly. What i'm saying, you may have a rod bearing thats been contaminated...

^^^ this is worse case by the way..... but take it easy as it is still servicible if this is the problem, dropping the sump, changing the rod bearings in situ..... if you kick it and it fails.. it'll take the crank out with heavy scoring and the whole lot will have to come back out.

Really, you need to stick someones head at it thats used to all the noises these engines make... diagnose it in seconds....

[mazzerdod]

Hi thanks for the input no prob with oil pressure everything is very good!!

The car went to the machine shop yesterday and the engineer has confirmed the noise is piston slap.

It was a friend who took it down so wasn't a party to the conversation he said it was because of the tolerance required for the forged pistons and that it will be worse when cold.

That's about all I know he didn't seem to think it was excessive or would cause any problems so we'll finish the run in and see how the car performance!

[Jim Galbally]

how did you run the cam in