Valve Touching Piston

[wardy18 33 1 Cars]

I stripped the XU10 head of my XU9 block the other day only to find the following exhaust valve marks on each piston.....

 

I can only think this is due to too advanced cam timing on the vernier pulley

 

Can anyone confirm?!

 

Also you'll note in the closer shot of the cylinder 1 that the gasket is about to s**t itself!!

[Miles 331 1 Cars]

Without knowing the spec or timing you cannot say but when adjusting it you should know what it's set too, But they are 16v pistons as you no doubt know, the old Omega Piston's (8v) had nice big cut outs for this very reason, The cambelt end is Cylinder 4 for referance

 

Is it a 1.9 gasket?

[wardy18 33 1 Cars]

As you say, yes they are Mi16 pistons to increase the cr. Off the top of my head i cannot remember cam timing but i do remember it was oh so very slightly more advanced than recommended.

 

Std 1.9 gasket too yes

[Sandy 191]

The cam would need to be retarded for the exhaust to touch and not the inlet, assuming the valve heights are similar. Advancing it too much would cause the inlets to touch.

[wardy18 33 1 Cars]

very odd then

 

All else I can think then is that in the crash somehow the timing belt got itself a massive gash and had torn half way through the width, maybe it skipped a tooth and retarded itself causing then exhaust valves to kiss the pistons as the engine was winding down after I hit the wall

[Cameron 16]

Could well be that, if your pistons were kissing the valves for any length of time I'd have thought the engine would have s*it itself before too long.

[DrSarty 90 1 Cars]

Could well be that, if your pistons were kissing the valves for any length of time I'd have thought the engine would have s*it itself before too long.

 

Agreed. Would've been noisy too wouldn't it?

[rescue dude 0]

I'm not saying this is the reason but i've seen similar mark's on piston's when an engine was badly over revved causing valve bounce.

 

The over revving caused it to "put a leg out of bed"

[wardy18 33 1 Cars]

I'm not saying this is the reason but i've seen similar mark's on piston's when an engine was badly over revved causing valve bounce.

 

The over revving caused it to "put a leg out of bed"

 

This also brings me to another issue that i dont think my rev limiter was working, was intending on testing it at the sprint event until i threw it in the wall

[tri_longer 25]

excuse my complete ignorance, but aren't the cut outs on pistons meant to allow for the valves, in which why is you valve mark smack bang in the middle?

[Cameron 16]

He's used 16V pistons for higher compression.

[wardy18 33 1 Cars]

Fitting the Mi pistons was because i fitted a XU10 8v head with std height (no skim) which was meant more for the new 2.3 block but i fitted onto the 8v 1.9 block as i had to swap my cam over to the new head. With the new head the combustion chamber was much bigger (also being a 86mm bore cc) and so giving me very little compression.

 

I later found after fitting the Mi pistons that they were an earlier type (or somethin to that effect) that actually sat approx 0.4mm down the bore instead of flush as with std 1.9 pistons

 

All in all i thought i was pretty safe to still run the same cam advance, if i remember rightly, something like 3.65mm at TDC.

 

It went well with no rattles or knocks and was quicker by 2 - 3 tenths on a qtr mile sprint over the std head with a heavy skim.

 

 

I can just put it down to either valve bounce due to limiter malfunctioning, or jumping a tooth when the belt took a chuck out of itself!!

 

Either way i will get the ead fully tested before fitting to the new block

 

Thanks for the help

[Miles 331 1 Cars]

Did you check the engine when it came apart, in was the timing still in the set position?

 

As said get the valve's checked before you do anything

[wardy18 33 1 Cars]

Unfortunately i thought all was well so whipped the head straight off without looking at the timing

[Sandy 191]

I should have gone on to cover the other points mentioned. A skipped belt would lead to exhaust valve contact ultimately and over-revving and/or insufficient valve spring control will tend to show on the exhaust.

[wardy18 33 1 Cars]

My question now going forward is, if i can see the full circle on the exhaust valve on the piston top does this mean they will all be bent now or do they come down flat to the piston anyway?!

[rescue dude 0]

If I were you i'd get a new set of valves just in case.