Oh no I've taken it apart

[Mezo]

I would expect damage to the valves & marks in the chamber if something was rattling around?

Mezo.

[xtzrick]

Looks like detonation to me.
Possibly caused by carbon build up in the squish area

I'd expect more damage to the edge of the combustion chamber if it was a foreign object.

Rick

[xtrider]

I'd have to concour with it being particle damage(chunks of carbon) not detonation . Detonation at that extent would have destroyed the piston pretty quick and violently(probably broken in pieces and taken out a valve with it) . There would probably be damage down by the valve also from the broken piston hitting things (unless it was shut down in time).

The most damage is on the exhaust side , the side that the piston rocks and comes closer to the head ,the reason many wrist pins are offset to stop it, XT's are not. Someone didn't verify enough clearance to begin with on a previous rebuild so the piston wouldn't come so close and hammer carbon chunks into the head. The bottom end should be checked for signs of broken piston skirts being smeared around by the crank.


Measure the bore and makes sure it doesn't have more than .0032 to .004" clearance over the piston shirt .500" from bottom 90 degrees from wrist pin. If it's at the max or above it will be a loud ,rattle motor from the piston knocking. They are fussy that way. .0025" is ideal to me but a person can't just start the motor up and hammer the throttle , the piston will seize if not allowed some warming up.





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[xtzrick]

However the holes were made I think I'd be looking at getting them welded over then the head skimmed flat.

They look perfect for catching carbon deposits & starting the carbon build up all over again.

Rick

[bigiain]

Thanks for replying guys
I think it is debris related as when I look closely there are a couple of dings on the ridge of the combustion chamber.
Will stick the head into a machine shop I use and get it welded and skimmed one of the rocker cover threads is stripped anyway so can catch that as well.
How do you see fifth gear without splitting the cases or do you think I should split them anyway while I'm this far in?
Think I've just answered my own question

[Mezo]

You should be able to see the gear faces peeking down past the crank, if you see the faces chipped then time to split.



Mezo.

[Fred333]

I think , you can live with that dings on the headcombustionchamber.
Welding is to harsh to the head. deforms it.
There was something flying arround in the cylinder.
It is out now.... so everything is ok.
Just my thought.
Cheers Oliver

[xtrider]

I'd take a small disc sander and lightly sand some of it smooth or at least take some of it down and shave .01" off the mating surface to make sure everything is nice and flat . The dent themselves probably won't do much harm but I like to minimize them if possible , too much to weld . They may even cause a bunch of turbulance which is good for getting the air/fuel intake charge mixed more homogeneity.




.

[Mezo]

They may even cause a bunch of turbulance which is good for getting the air/fuel intake charge mixed more homogeneity.

Im guessing that must be what my old man used to describe as "Swirl"

Mezo.

[xtrider]

Don't know what he was considering swirl . To me swirl for the intake charge is making it look like a tornado (cyclone for those on the upside down part of the world )
kind of how water goes down a toilet when flushed , only its the air/fuel mix going into the cylinder. That can be turbulence , but to me turbulence is just upset or random patterns of air movement , or picture how air would move over a bunch of bumps and grooves causing a bunch of low pressure zones and the air tumbles like an ocean wave rolling over a coral reef. All this makes the charge more homogeneity -aka- every cubic inch of air has the exact same parts per million of gas molecules as the next and burns consistent (efficient).




Boy what a load of bull .