2F - Broken Rings - 2nd Compression Ring

Joined
Aug 16, 2006
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383
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Jhb - South Africa
This is a copy of a post in my rebuild thread

https://forum.ih8mud.com/40-55-series-tech/224775-south-african-bj40-rebuild-into-fj40.html

Those of you that have been following this thread will know that I picked up an engine knock from continually driving the truck to overheating in the Kalahari Desert in December. :bang:

Before I went to Europe I pulled the motor and cogbox out in preparation for pull down and rebuild.

Well. Yesterday I pulled the motor apart and sh1t did I get a shock.:whoops:

I lighted sanded the top of the cylinders with abrasive tape to prevent the possibilty of the rings snagging. Wasted my time :hmm:

The 1st piston I removed was no 6, the second compression ring was broken into about 10 pieces. :confused:
The 2nd piston I removed was no 1, the second compression ring was broken into about 15 pieces :confused::confused:
The 3rd piston I removed was no 5, the second compression ring was broken into about 8 pieces :confused::confused:
The 4th piston I removed was no 2, the second compression ring was broken into about 6 pieces :confused::confused:
The 5th piston I removed was no 4, the first (top) compression ring was broken into 3 pieces, and the second compression ring was broken into about 15 pieces, and the piston had 4 score marks down its side (but no damage to cylinder) :confused::confused:
The 6th and last piston I removed was no 3, the second compression ring was broken into about 4 pieces :confused::confused:

My assumption is as follows;
the fact that I was constantly driving the truck in 45deg ambient temps in the desert, to the point of overheating, then waiting for it to cool down then continuing on further until it overheated again, and this continued for over 500km, has accounted for the broken rings and no 4 was the first piston to break its rings (but:- assumption is the mother of all fekkups)

BTW - when I rebuilt the motor - the pistons were Yota original, but the rings were from Terrain Tamer - Aussie.

I would be very interested to hear any and all other theories on the causes of ring breakage especially when it is only the 2nd compression ring.
 
Joined
Oct 31, 2003
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Meridian,TEXAS
Three Ring Circus...........

Has a lot to do with the composites the mfg choose to use........

On many, the top ring has a gas nitride, chrome or moly coating to improve durability (dissipate heat).......less likely to bind-up and break.........can withstand temps over 600*..........

Most second rings have a tapered face with a negative twist. This creates a sharp edge that scrapes against the cylinder wall for better oil control (no protective coating)if there was, oil would slide-by ........thus results in a more brittle ring especially when cooked over 300* ...............

Just consider your self lucky.......more damage could have been done.........
 
Joined
Jan 14, 2007
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577
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Stafford - UK
What end gap did you have on the rings when you installed them? I wonder if a tight clearance and heat could cause broken rings.

I have never have to do rings on a 2F but when I last did rings on a silimar size piston I used something like 0.4mm on the top and 0.5mm on the second ring, 0.016 inches and 0.020 inches.
 
Joined
Aug 16, 2006
Messages
383
Location
Jhb - South Africa
What end gap did you have on the rings when you installed them? I wonder if a tight clearance and heat could cause broken rings.

I have never have to do rings on a 2F but when I last did rings on a silimar size piston I used something like 0.4mm on the top and 0.5mm on the second ring, 0.016 inches and 0.020 inches.
I cant remember the specifics, but I did gap the rings according to the manual before installing them onto the pistons
 
Joined
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For those of us that are to lazy to read the build thread explain in short what brought on the overheating issue........

And while your at it, post up a pic or 2 of the carnage.........
 
Joined
Aug 16, 2006
Messages
383
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Jhb - South Africa
When I removed the B diesel motor from the 40 and replaced it with a 2F that came to me from a friend in Namibia, that was originally installed in a 60 series.
It came to me with a fan and viscous coupling attached to the water pump.

When I rebuilt the motor I ordered a new viscous coupling and a fan with the same diameter as what it was supplied to me with, as I assumed that this was the correct one, this turned out to be the mother of all fekkups - I should have ordered the fan according to the 40 series 2F toyota part number - but - hindsight is a perfect science.

To cut a long story short the fan that I originally fitted was about 100-120mm smaller in diameter than the one that I later fitted (after the overheating drama)
The lack of airflow (pull) into the radiator in the 45deg C ambient temperatures of the Kalahari Desert resulted in t constant overheating

Unfortunately it is now too late for pics as the motor is already at the machine shop getting machined ready for the rebuild.
 
Joined
Aug 16, 2006
Messages
383
Location
Jhb - South Africa
Cause of broken rings found

The machine shop found the real cause of the rings breaking :frown:

The ring groove in the piston is 4mm
The thickness of the 2nd compression ring is (was) 3.0mm
This meant that on every stroke the rings were rattling around in the piston ring groove at 2000 - 3000 rpm until they self destructed.

As previous mentioned, the pistons are original Toyota parts, but the rings were aftermarket rings supplied by terrain tamer in Aussie, obiviously the 2nd compression rings didn't match the pistons.

The top compression ring and the oil ring were correctly sized - so was this just a mismatched set ???
 

lostmarbles

SILVER Star
 
Joined
Sep 3, 2007
Messages
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New Zealand
The machine shop found the real cause of the rings breaking :frown:

The ring groove in the piston is 4mm
The thickness of the 2nd compression ring is (was) 3.0mm
This meant that on every stroke the rings were rattling around in the piston ring groove at 2000 - 3000 rpm until they self destructed.

As previous mentioned, the pistons are original Toyota parts, but the rings were aftermarket rings supplied by terrain tamer in Aussie, obiviously the 2nd compression rings didn't match the pistons.

The top compression ring and the oil ring were correctly sized - so was this just a mismatched set ???
Ask for comment from Terrain Tamer!

(As far as I know they are a reputable company who sell good products. - In fact, I wish they had a better distribution network so I could get my hands on more of their stuff.)
 
Joined
Oct 31, 2003
Messages
5,025
Location
Meridian,TEXAS
The ring groove in the piston is 4mm
The thickness of the 2nd compression ring is (was) 3.0mm
This meant that on every stroke the rings were rattling around in the piston ring groove at 2000 - 3000 rpm until they self destructed.
Yeah, that'll do it........

Someone should have been more careful during the assemble.....
 
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