Been having compression issues of late on cylinder three. Convinced myself the head was a fault, so invested in a flowed head from AL Developments when I found a oversized lifter. Bolted the head on yesterday, and compression was still down to 77psi (other three are at 155 to 166psi). So took the plunge dropped the sump, pulled the piston and rod, and found this ;;






Think its safe to say, I may have found the culprit. Its taken me from October till this morning to do this, as I really didnt want to pull my none leaking sump off.

Hey ho, my April 10 deadline is pretty impossible now I guess.

 

think?

I think so too mate.

 

not hard to find another piston or a set.

 

Is the bore ok?

 

like me on a saturday night pissed n broke

 

My mate has a set of standard RS pistons up for sale. I will ask him if he still has them.

 

Bore is sound. Car hasnt moved since it happened. Order myself a set from a breaker. Gonna invest in some forged ones later in the year when Im more flush.

 

When you put the new sump gasket on, the key is to torque the sump correctly. I fitted a new one last year, worked perfect first time. I used the old trick of super gluing it to the block before fitting the sump pan

Lee

 

Way it worked for me in the end was to buy a new sump, superglued the gasket to the sump, left it for a week, just over hand tight the bolts, and nip up where required while car was running. Hopefully it will work again.

 

Cracked ring lands, classic sign of detonation, any det marks on the top of the pistons? Either way be sure to have it setup once you have rebuilt it or you may find it happens again.

Are you sure the bore is ok, this photo looks like the top of the pistons has been scraping?

 

Car gets set up every time I do any work to it. Think No3 has always been week, as compression was always lower than the others.

Bore is sound, Ill get some pics up in morning.

 

What sort of power were you running mate?

 

Car is 197bhp, & 222ftlb, @ 15psi. Have all the supporting mods, Pro alloy front mount, airtec rad, arp's, scorpion, K&N, blitz boost controller, bayoo stage chip, baileys breather, samco's etc.

As you can see, the bore is sound, Im a very lucky boy I think.

 

So long as those light marks cannot be felt with your finger nail I think it does look ok, very lucky mate!
At that power a piston should not be breaking, have you a photo of the crowns?

 

Cant feel a thing Ill get a pic of the crown up soon. Thats what threw me, as it looks ok. Im a NDT technician, so ive tested the piston and bore cracks, and found nothing.

 

 

The crown of the piston looks fine but the side above the first ring groove has det pitting on it. That'll be the cause of the ring lands breaking off.

 

Should I pull pistons 1, 2 & 4 for a look-see to be on the safe side, even though the compression is spot on?

When looking around google, here etc, i see most problems with pistons on the RST are No3. Any reason why that is?

 

Yeah as expected detonation looks like the cause, where do you have it setup, are they familiar with RST's as a lot of tuners are not these days?
Yes pull all pistons and inspect them as the may be others waiting to fall apart too.

 

I use Evotune in Durham. Jamie is a old school Ford boy and knows his beans.
May be a thickie question, but can l reuse the piston rings on the good pistons if i take them out for a look?.

 

Assuming you hadn't recently turned your boost up or advanced the dizzy (since you're last setup) it could be that your metering unit is drifting out or calibration (very common), your ECU MAP sensor has failed (also very common) or just a problem with No 3 injector.
If the the other pistons are all fine then technically yes you can just put them back in, but I wouldn't recommend just fitting one replacement piston, you have to take the block out to have the bore honed so may as well do all four (you may even find once the bores are measured you need to go oversize anyway).

 

Sod that mate. Just find another piston and put it in. Your start taking it apart and you might aswell do it properly and build with decent parts.

I have pistons that you can throw into that for free pal. Get it back together and use it. If you want a propetr engine build one. Dont waste money on that.

 

Ive done a combination of both of the last two replys.

Pulled the pistons, and they look ok, so just popped them back in. Ive got a new standard Mahle one from Burtons, and its going in next weekend. I intend to forge the bottom end over the winter, so this only has to last six months or so. Im adament Im sticking CVH MFI, as old school is my thing, but want it to be as safe, and as well built as possible.

 

Sounds sensible.

 

Make sure you find the cause of the detonation and put it right, or you will end up in the same situation again mate.