Cracked piston?

[Ando81 2,949]

Hi all, as the title suggests I think I have got a cracked piston. I bought this engine that was supposed to be rebuilt 50000km ago. It was an R.P.M Engines job and it has +.040 Pistons in it but I reckon the top of number 1 piston has a crack in it. I took the head off to replace the gasket and discovered the damage. Can anyone confirm that it's definitely a crack or could it be something else. Cheers

[slydog 7,873]

Did it have blow by when running ?

[wagoon 2,429]

Can't say I know much about pistons and the internals of an engine but that looks to me like just a mark in the metal. It looks like a gouge or indentation made by something that has entered the combustion chamber, I have seen plenty of cracks in metal and to me that does not look like a crack in metal.

[Ando81 2,949]

I only saw a video of it running and basically only bought it sight unseen coz it was a good price. Seemed to be fine but I have bought a better cam to put in it and after seeing the bores in very tidy condition I thought I'd leave the pistons & rings. Till I saw this I must say.

[ando76 4,354]

Doesn't look like a crack to me.  For the price of a sump gasket you can whip it out and check.  It may just be that someone dragged it across the bench or dropped something on it - or foreign body damage thru the intake as Ryan has said.

 

You have to remember that most people treat these things as taxi motors and don't give them the respect of love they deserve.

[Ando81 2,949]

^^^^ thanks for the positive input lads, Ando I'm not very confident about pulling a piston out. I've always thought i would stuff something up. I think that's the best way to go though just to make sure that it doesn't shatter under acceleration. I think the fella that owned it before me used to thrash it pretty hard so it's a wonder it hadn't let go already if it is a crack.

[Nath 1,975]

If it's been flogged you'd think it would have exploded by now if it was going to...

[slydog 7,873]

If it's flogged its well run in for a xflow is all.

[Nath 1,975]

If it's flogged its well run in for a xflow is all.

Yeah I thought cold limiter bashing it up the road was the most efficient way to warm it up?

[Ando81 2,949]

If you flog it too hard, somethings gotta give! Where is unfamiliar when you need him

[slydog 7,873]

Well in the non rude style a stock xflow piston is a tuff piece of kit. Can't bust em unless you rev to 7000plus and your fuel pump is a POS unit that falter's LOL

[wagoon 2,429]

If you wanted to check the piston while still in the block you could use a dye penetrant test kit. You get them from tool or welding shops. They come in a 3 part kit. The first spray can is used to clean the metal surface(no grinding is needed on a piston surface but a clean with 1500 grit paper would be good) Part 2 is normally a red dye that you spray onto the metal surface, you let it sit for the amount of time the directions say. You then spray the cleaner(part 1) over the surface again but not directly into the crack, you can use a rag to wipe the piston in this step. All you are trying to do is remove the red dye from the surface. The you use the 3rd part which is a white spray known as the developer to expose any cracks. The cracks will show up as red lines cause the dye has penetrated into the crack and the white shows the red dye up. That's why you don't spray the cleaner directly into the crack.

I do this sort of crack testing a lot at work and it works fine and it should work in this situation so long as you clean the top of the piston first with a bit of fine paper. I would remove the sump as well as both the cleaner and excess dye will end up in the sump otherwise. Then when you have checked the piston just spray part 1 of the kit down the bore to remove any excess dye and developer as part one is an alcohol based cleaner it will evaporate anyway. Then new sump gasket head back on and your away.

[Ando81 2,949]

Thanks mate, the engineer at my work has a kit like this and I was wondering how it worked. Great explanation, it sounds like a good way to test it for sure

[gerg 10,871]

Just looking at the pic (zoomed in to max), it does indeed look like a crack, but depending on how far down it goes, could be superficial. Could be caused by a casting flaw or inclusion, not necessarily from being thrashed. If so it's in a very unusual place.

 

It's not on the thrust side (I can see the pushrod galleries next to it) so only thing that I could think of is detonation. Pistons often crack around the skirt from excessive side-load or at the gudgeon from the obvious push/pull loading.

 

That's only if it is a crack. If it's just a scratch, happy days.

[Ando81 2,949]

I was thinking maybe it could have been from heavy acceleration with bad timing and pinging. I'm thinking I need to polish the piston up and inspect further and if it's still inconclusive I'll have to pop the piston out to double check.

[PRO250 1,506]

Looks like a scratch to me if you want a piston messure the dish and ill send you a piston and a rod and you can jam it in and go again looks like a 22cc or 29cc ACL slug hope (hehe ripe for boost) id put money but looking at the top end the engine will likely need some work so id leave it and run it  

Id run that in a stocker but if your worried about it get a bit of 240 wet and dry and a can of WD40 and rub t till the scratch is gone you will then see if its a crack I think its just a scratch

I got a 250 a while back that I trashed senseless it had no issues at all but it has a side off a piston, these engines don't need piston tops to run is what im trying to say   

Hell if you want a new set of pistons I think I have a 6 or 7 sets in the corner that engine needs less dish anyway unless your,,,, cough couch boosting it

[bear351c 10,271]

Magnaflux it, baby.......!!

 

Looks like a groove, not a crack.

[Nath 1,975]

Sikaflex fixes everything.

[Ando81 2,949]

Thanks for all the input lads, tonight I gave it a quick rub with wd40 and wet & dry. The scratch is now gone

[Ando81 2,949]

[ando76 4,354]

fixed.  Me - Id still pull the sump - undo the 2 rod bolts (1/2" socket) and pop the piston up.  If you don't own a ring compressor - then just go steady steady and push the piston out enough to check the top before the top ring.  If no crack present, push is back down and do the 2 bolts back up.  33nm. Job done for sure. 

[wagoon 2,429]

WOW that cleaned up really really well. Win for you well done.

 

Got to agree with Pro on the boost as well.

[hendrixhc 10,921]

Id get the autosol out and polish it til you can see your teeth in it.

[Ando81 2,949]

The photos don't show it really well Ando76, but I reckon you're on the money, I should confirm that it's all good.

[Ando81 2,949]

Id get the autosol out and polish it til you can see your teeth in it.

 

Till it looks like chrome?