Pressure testing block

[Mc Tool]

I got a 3.9 Rover for the Capri , these things have issues with water jacket /cylinder bore concentricity and can crack the jacket behind the liner .

So I blank off all the holes ,fit a pressure gauge and valve and put 30psi in there, which it held for over 24 hrs , so I did the other side , was good too, Yay

Check the top of the piston . These marks (there are nother 3) line up with the exhaust valves . Mmmmm

[Major_Tom]

What effect does damage to the piston like that have, if any?

[Mc Tool]

It causes a point where stress cracking up can start.......Im ok at the moment tho .
I dont think it will hurt the piston any, Im not planning on replacing them as they measure up well. I will either file or pien the high spots down a bit tho . The valves look fine too, checked them with a dial gauge and was surprised they weren't bent. Maybe hydraulic lifters may cushion the blow a bit .
There is something fishy going on with this motor . The cam and followers are worn ,as is the camchain and sprockets, bearing shells are worn thru 2 layers , the whole motor is filthy inside .....but the cross hatching is still well present over the whole of the bore surface .
Sadly I didnt have the presence hof mind to check the cam timing before dismantling as its possible the chain may well have jumped a tooth or 2 . This would retard the cam , holding the exhaust open a bit long around tdc, which could explain the contact marks. The cam chain was really flapping about in there........that crap nylon coated cam sprocket doesnt help either.

[Paul G]

I've seen pistons a lot more pitted and damaged than that and when repairing vehicles that have had a cambelt snap you will invariably see marks in the pistons where the valves have impacted but once the head is repaired they continue to give a long life.

If you drive the vehicle like a see you next tuesday or on a track it could possibly slightly increase risk to the piston but it's a risk I would take.

[SCP440]

I've seen pistons a lot more pitted and damaged than that and when repairing vehicles that have had a cambelt snap you will invariably see marks in the pistons where the valves have impacted but once the head is repaired they continue to give a long life.

If you drive the vehicle like a see you next tuesday or on a track it could possibly slightly increase risk to the piston but it's a risk I would take.

I agree, only recently I was helping a friend do the headgasket on his car and when we removed the head it was obvious at some time there had been some impact damage from valves hitting the pistons from a broken Camblet at sometime in the past, he has had the car for 5+ years and it has never been a problem.

[Mc Tool]

They measure up as new , inc ring grooves , and Im pretty sure I know why/how it happened so in they go .
I have a pinto piston that munched one of them spring washers that hold the carb on......