Are these precup cracks normal?

[Curt]

As per title, just wondering if these are normal or something to be worried about:







I know cracked precups are commonplace but just concerned some of them are a bit much.

Cheers m' dears

[Tom]

They do look quite big but i think its normal...

[Chris_90]

If my pre cups was cracked like that think I'd throw it away, but I no nothing about them so probably be fine.

#uselesspost

[Ruan]

You'll probably find that after a skim they'll largely go away...

At least, I've skimmed and reused worse.... The ally isn't bulging past them or anything, so should be OK Tbh... Get it pressure checked and skimmed, should be fine...

[Piggy]

Yeah, I seen worse and have never seen a head come off without cracks there

[Chris_90]

Yeah, I seen worse and have never seen a head come off without cracks there

My head didn't have a single crack on the pre cups no idea why that was then........

[Ruan]

Probably been skimmed recently.

[Chris_90]

Probably been skimmed recently.

Yer I had it skimmed. Might have been some before but didn't look tbh.

What causes it to crack like that then?

[Ruan]

Heat - it's the main reason Peugeot went away from Indirect injection once CR Direct and computer airflow simulation came in - the precups need to stay hot to keep the next combustion cycle clean and smooth, but understandably under high load, keeping enough heat in them for the next combustion cycle vs them overheating vs requiring too long to heat up on cold start is a fine line.

When you tune them, trust me, those cracks become significantly worse!!! As Darren found - they can end up being released from the head in the end...

Remember, these things take the full brunt of *every* combustion cycle for that cylinder - the burning hot diesel floods past them every stroke.

If you're interested, at 2750rpm that's 330,000 times every hour they have diesel, midway through combusting rammed through them.

[Curt]

Cheers guys, good to know it's usable. It's not getting skimmed as it's from a known good engine which was running fine. If it wasn't for money and time constraints, I'd get it done anyway... But that's not the case.

[Chris_90]

Heat - it's the main reason Peugeot went away from Indirect injection once CR Direct and computer airflow simulation came in - the precups need to stay hot to keep the next combustion cycle clean and smooth, but understandably under high load, keeping enough heat in them for the next combustion cycle vs them overheating vs requiring too long to heat up on cold start is a fine line.

When you tune them, trust me, those cracks become significantly worse!!! As Darren found - they can end up being released from the head in the end...

Remember, these things take the full brunt of *every* combustion cycle for that cylinder - the burning hot diesel floods past them every stroke.

If you're interested, at 2750rpm that's 330,000 times every hour they have diesel, midway through combusting rammed through them.

Oh very good info! Learn something new every day

[Piggy]

Cheers guys, good to know it's usable. It's not getting skimmed as it's from a known good engine which was running fine. If it wasn't for money and time constraints, I'd get it done anyway... But that's not the case.

Shop around dood...

Its just not worth NOT doing.

Otherwise it goes wrong and you end up stripping it down, skimming it anyway and getting another set of headbolts and HG

[Matt]

Angle grinder? Cheap right......

[Curt]

Haha, plan. What could possibly go wrong?

[Niall]

Cheers guys, good to know it's usable. It's not getting skimmed as it's from a known good engine which was running fine. If it wasn't for money and time constraints, I'd get it done anyway... But that's not the case.

Shop around dood...

Its just not worth NOT doing.

Otherwise it goes wrong and you end up stripping it down, skimming it anyway and getting another set of headbolts and HG

Sorry but i don't 100% agree with this. Whats the point in skimming it if you check the face is flat and its ok? Can be done fairly easily with a proper straight edge and is quite common practice.

[Curt]

Exactly my thinking. If it had overheated or blown then it'd be different, but that's the whole point in using this one instead. Plus it didn't cost anything, which is important at the moment.

[Dave]

Check it's flat and use my friend, my cups are 50x worse but they never seem to get worse unless I push more and more power.

[Curt]

Cheers Dave, it's not as bad as I thought then