intercooling

[jontysafe]

If this is the right pic it should show a chunk of aluminium out of the head next to valve.

[stevieturbo]

What were valve clearances like on that side ? Almost looks like the valves werent sealing properly among other problems.

Not really sure that's detonation damage either. What are the pistons like ?

[jontysafe]

What would it be if it wasn't det?

One piston has melted big style. Melted is probably the wrong word, more holed.

[stevieturbo]

jontysafe said:

What would it be if it wasn't det?

One piston has melted big style. Melted is probably the wrong word, more holed.

Lean mixtures and/or too low timing causing huge EGT's

Although obviously lean mixtures can make the engine more prone to detonation too.

Are all 4 similar ?

pics of pistons ?

[jontysafe]

Only one piston is damaged. Can't get pics at the moment.

[jontysafe]

Only one piston is damaged. Can't get pics at the moment.

[jontysafe]

Only one piston is damaged. Can't get pics at the moment.

[Boosted LS1]

Pardon? It'll fettle out but you need to fix the issue.

[anonymous-user]

Looks like classic minor det leading to pre-ignition to me!

[jontysafe]

Would changing from bd14 inlet and bd8 exhaust to bd16 inlet and bd14 exh be enough to out the fuelling out at high revs? I know the answer is probably yes.

The issue was due to be sorted the following week with a live map.

[Evoluzione]

I'm presuming you've spotted the cracks?

It suggests to me that major overheating of the exhaust valve and seat area (the causes of that are numerous) has brought on det, i'd be interested to see a pic of the piston, if you can, hopefully you can also tell us which way round the crown was in relation to the head.

[jontysafe]

I hadn't spotted the cracks, can you point them out?

Do I buy a new head or fix the existing one?

I will ask for pics of piston.

[Evoluzione]

The engine builder should be able to tell you all this and you shouldn't have to ask for advice on an internet forum. If he can't you need to carefully consider your options.

[Evoluzione]

jontysafe said:

If this is the right pic it should show a chunk of aluminium out of the head next to valve.

Looking on that pic, the upper valve seat has one starting at 9.30, both have possibles radiating from seat to spark plug hole, but it's difficult to say for sure as they are covered in carbon which needs cleaning off.
Without having it in front of me and/or having it crack tested I couldn't be 100%, but I'd be looking at that and it's causes before going much further.

[stevieturbo]

Ive seen heads cracked silly and never actually caused any issues.

But it's just too hard to say from the photos, but the damage looks fairly minor.

But really, almost anything is repairable given time/money

There's nothing there that wouldnt be difficult to fix.

[jontysafe]

Just trying to work out whether i would be better off getting another head that's already ported to the same standard.

Need to find out head thickness.

Engine builder has advised fixing this one but will probably be about 800-900 squid finished ready for fitting.

[stevieturbo]

jontysafe said:

Just trying to work out whether i would be better off getting another head that's already ported to the same standard.

Need to find out head thickness.

Engine builder has advised fixing this one but will probably be about 800-900 squid finished ready for fitting.

Cossies are old engines, so finding a good base head to start with could be as much a problem as having your own repaired.

But at least you know some history of your own and its' condition.

If yours has already been ported and is a good job, just repair it.

Although what does that £900 entail ?

[jontysafe]

Welding up of the three combustion chambers and taking back to standard again. Skimmed , pressure tested, new stem seals.

My head is has only ever had an. 8thou skim, most cossie heads out there are skimmed below where the head is actually jiggered.

[226bhp]

If you have those cracks welded up you'll need new valve seats too.

[jontysafe]

Yep, includes cutting new valve seats.