Example of piston ring groove failure on 12ht (1 Viewer)

[Christian]

I was at the engine rebuilder today, and took this picture:


This piston came out of a running engine, that on top of this had one bent pushrod and a broken one!

I thought I would post this as an example on the weakness of the 12ht pistons, so people could see the actual problem and so it could be found when searching for the issue.

 

[raboyto2]

I dont know much about this failure, but I do like your Knipex pliers.

 

[blis]

That is not even the worst one I have seen... In the worst you could fit 2 rings in the groove...

 

[Radd Cruisers]

Yes, we're quite aware of this problem and supply only the Alfin style pistons in the engine kits we carry.

I have a few 2H pistons kicking around that just look like this as well.

~John

 

[ozwallaby]

To those with experience.... I've only seen 3 or 4 12hts apart and haven't seen this, though I'm aware it's a problem..... is the wear normally on the TOP side of the ring land or can/does it happen to both/either...

and do the Alfin pistons mentioned have inserts that strengthen top and bottom of the groove and also more than only the top ring groove....

 

[shanko]

Info on the Alfin piston inserts

Oxwallaby,

Here is some information on the piston ring land fractures and Alfin piston ring groove inserts from the Engines Australia website (http://www.engineaustralia.com.au/).


ALFIN INSERT - A high nickel cast-iron insert, which is cast into a piston and machined to carry the top ring and sometimes the second ring also - thus RING CARRIER. The insert is made of metal known as Ni-Resist in the industry, and is an Austenitic cast iron (non-magnetic) with 13.5 - 17.5% nickel and 5.5 - 7.5% copper. It is chosen for its high wear strength and co-efficient of thermal expansion similar to aluminium. The trade process of inserting the Ni-Resist ring was developed by the Fairchild Engine and Airplane Corporation after World War 2 and is called Al-FIN (Aluminium FIN). Also known as Ni-RESIST INSERT or RING CARRIER INSERT. For further reading see Service Engineering Bulletin SB015.

​

Service Bulletin SB002 Prevention of Piston Ring Land Fractures ->
http://www.engineaustralia.com.au/~engine/sites/default/files/SB002.pdf

Service Bulletin SB015 Alfin (Ni-Resist) Ring Groove Inserts -> http://www.engineaustralia.com.au/~engine/sites/default/files/SB015.pdf

Cheers,

-Sean

 

[ozwallaby]

Thanx for that Shanko..... will look at the suggested info...

 

[cruiserpilot]

How bad does a 12HT have to be running to look that bad, as in the top pic? If I remember Christian, you had 500K on this motor?

 

[Dougal]

Looks like that piston got very hot too. Likely the original cause of failure.

So 12HT pistons aren't ALFIN? That's weird, turbo Isuzus of the same vintage were.

 

[ozwallaby]

Looks like that piston got very hot too. Likely the original cause of failure.

So 12HT pistons aren't ALFIN? That's weird, turbo Isuzus of the same vintage were.

I wonder if they changed with later 12hts..... I haven't seen any ALFINS but I haven't seen inside many 12hts either....

 

[Christian]

How bad does a 12HT have to be running to look that bad, as in the top pic? If I remember Christian, you had 500K on this motor?

This is not from the engine that failed, this is from another one I had bought approx. a year ago.
I was told it had started "rolling" (what we call it) in idle, going like 1,2,3,4,5,6,,,,1,2,3,4,5,6,,,,1,2,3,4,5,6,, but it ran... I have no idea of age, km's etc. but as I wrote I found one bend pushrod and one broken in half, with obvious signs that it had been running that way!

I just got word from the machine shop, the cylinders need boring to oversize, not beacuse of scouring, but because of rust. It has been sitting quite a while...
Crank etc. is fine.

AFAIK the 12Ht never got Alfin pistons from factory...

 

[buschmaster86]

But they would be a good preventive maintaince for this nice engine as they are becomming rare and expensive imo.

 

[Christian]

But they would be a good preventive maintaince for this nice engine as they are becomming rare and expensive imo.

Exactly, and changing pistons and rings are afterall alot less expensive than an engine with scoured cylinders...

 

[helocat]

Yes, we're quite aware of this problem and supply only the Alfin style pistons in the engine kits we carry.

I have a few 2H pistons kicking around that just look like this as well.

~John

How many KM in general do you think a stock 12HT should go before a preventative tare down to get upgraded pistons?

(Normal use, with care to not overheat the engine)

 

[buschmaster86]

from the treads i red about the engine about 400.000km but there are many many factors that influence it.

So its alway,s to early until its too late (****up i know)

 

[Christian]

One could keep an eye on blow-by...

 

[buschmaster86]

Good tip !! leak down test also now where at it.

 

[guistou]

Scary pic!!

I may need to open mine before disaster

Christian where did you plan to buy 12HT parts?? Europe? Australia?

 

[Christian]

Scary pic!!

I may need to open mine before disaster

Christian where did you plan to buy 12HT parts?? Europe? Australia?

Yes!

Australia should be the best source...

 

[guistou]

Some news?