new forged engine piston slap
 

hi

ive just recently had a forged engine buid, only done 300miles running in, ive noticed a rattle on start up from cold which goes as the engine warms, ive been told by the engine builder that its piston slap and is to be expected with forged pistons, do i have to live with this and is it normal?, i paid alot of money for this build and dont want to be taken for a ride and just want the engine to be right.

thanks

A small amount of piston slap is okay, if it becomes excessive i'd be having a word... the exact reason behind it being okay i'm not sure of, but i'm sure someone will be able to confirm. I was told the same thing by Harvey, Darren and Bob Rawle after mine was rebuilt with all forged internals... and i've 110% confidence in their work and knowledge.

pistonslap is to be expected with a forged motor. the forged pistons will expand when they get warm and fill the bore. so long as it doesnt use oil forget about it.

Forged pistons are usually installed with greater clearance than cast pistons. The expansion rates between the two are different and more cold clearance is required for forged to ensure good running fit when up to temperature. You only need a extra thousandth of an inch clearance to make the engine noticably noisier!
In a forged piston set up, I would be a bit concerned if there wasn't at least a bit of slap when cold!
Gentle acceleration until up to temp.

JohnD

Normal - I thought my forged (RCM) engine was fecked when i first started it, but when the oil gets to circa 75C it goes quiet, but that's a good 5 minutes after the oem water guage gets up to the normal range in these temperatures. As above take it easy until fully warm.

Forged pistons usually have a central gudgeon pin location, as opposed to an offset pin location on all OE pistons, as this helps reduce noise in this area.

This is completely normal.

All the above points are true, Forged pistons require a greater piston to bore clearance as they expand more when hot.

OE Pistons and some forged pistons have offset pins which will reduce noise. Most aftermarket pistons dont and together with the clearance required will be significantly more noisy than the OE piston.

As mentioned above oil cosnumption is key. If the engine isnt using alot of oil then you have absolutely nothing to worry about.

Although it will use more oil if the car is used for short journeys as in 3 or 4 miles to work each day

sounds like everything is as it should be then, theses comments have set my mind at rest.

Thanks

Well done for not jumping the gun and naming the engine builder before you were informed that everything was ok. That is the usual form, then a 20 page thread ensues, where everybody slags all engine builders, then the thread gets locked. A nice change from the norm.

Glad your mind is at rest.

my engine builder is highly respected on scoobynet, and naming and shaming was never really on my mind, i just wanted a few opinions on the rattle i have experienced just to put my mind at rest as im not an expert with engines, im happy with what im being told is quite normal, so i can now drive my car without any worries and continue the running in.

thanks

does anybody know the bore clearance if using forged pistons? i just took apart my standard ej20 block and while searching online for pistons i found out there are about 3 sizes. 92mm, 95 and 99 as i remember. how should i go about selecting a piston for me? Help pls :brickwall

Those are specific piston diameters for different capacity engines.
Your engine will have a 92mm bore so you would choose pistons with that nominal diameter. The recommended clearance will be accounted for by the manufacturer in production. If you have the bores honed then you will need to discuss this with the piston supplier.

JohnD

Building an engine you measure everything, 1 of them is bore clearence. Forged pistons manufactureres usualy recommend 3 1/2 thou clearence, however I run a larger clearence on my competition engines.

Rule is when warm the noise is gone.

Old group a wrc engines I used to build where noisey as hell even when warm, but they flew. F1 engines I used to build run a very tight clearence but try and hear slap off one of them on fire up!!!!

mines a 2001 jdm ej205 engine and it had been idling in one place for almost a year and when dismantled i saw a few corrosions had eaten away a small lump from the bore at the bottom where the piston had been. this is only on one bore. so i decided to go forged since i have dismantled the engine. the problem is whether i should hone all the bores to match until the dissolved patch levels up in the damaged bore or else to bore to a specific level like around 0.25mm or 0.50mm. My subaru agent warned me not to bore above 0.50mm piston ring size. The other option is whether to resleeve the damaged bore only and hone that to match the others and buy forged pistons to match that clearance.

If iam to hone the block to match std pistons which holds 0.50mm rings then which piston size should i use if iam going forged? is it 95 or any other size? iam confused at this area regarding these sizes so am halted and cannot proceed further until i know what iam doin and what should be done. HELP! :-O

The other thing is that iam looking at producing around 400 to 450bhp. without using a stroker kit which turbo should i go for? which would you guys suggest from the following?

*T3/T4 T04E Hybrid Floating Bearing Turbocharger .50 A/R .63 A/R (30+ PSI, 500+ HP Capability)
*TDO6 20G
*T70
*GT30
*GT3582R .84AR
*GT45
*VF36

Using alot of oil
 

Hi guys, I have a Wrx hatchback and it's running forged pistons and it's used 5L of oil in 3500 miles which I think is Alot, I took it back to the builder and they said its normal for it to use and needs a catch can to lower the consumption. Is that about right or is something wrong?

1l per 1000 is it the point I'd get worried, your over that so doesn't sound right that's for sure.

Wow that's a lot 5ltr in 3500k :eek:
A catch can will do diddly squat for oil consumption,a catch can is there to filter out the bad stuff which usually plumbs back into the inlet pipe and causes the octane rating to lower a little.

My forged hatchback doesnt need topping up at all in between changes , my last forged hawk used about 500ml every 4-5k miles

Sounds like something is VERY wrong to me 5L in 3500 miles IS excessive and anyone that says otherwise is talking out of their rectum. :thumb:

Return to sump catch can would reduce it... 'slightly'... but ultimately with those kind of consumption levels... something is not quite right.

Mind you at least you won't have to change the oil... as the engine is doing it for you. :lol1:

What would you suggest is the problem? Valve seals?

to use that much oil it must be smoking like a train, or else actually leaking out of somewhere - have you had the undertrays of it to inspect for oil leaks?

If you removed the valve stem seals it wouldn't use that much oil, what pistons are in it, & what clearance were they honed to ?

As above, bore to piston clearances... is the obvious choice... Paul aka Motors GT will be able to answer your questions better than just about anyone else on here. :thumb:

Omega pistons, as to what clearance I don't know that sorry

You have a good quality piston, depending on clearance, & more importantly bore finish is key to good ring bedding in & ultimately oil consumption.

Thanks for the help, I'm taking it to scooby clinic on Monday so see what they come up with if it is that

I have mahle forged pistons supplied and fitted by motors gt, no noises and hardly uses any oil between the six monthly changes. Engine has done over 10000 hard miles so far.