cjtamu

iTrader: (11)

Running a .12 OS TZ in my GT2. This one is a cut threaded crank with about 1.5 gallons through it. The last couple of times I've raced it, a couple things have happened. After the engine sits for a few days the cold pinch is tight. And I mean like new engine tight or a squeezed sleeve that's been pinched too low, the piston sticks if you roll it just barely off BDC. Have to heat it with a gun to about 170 just to get it to start. I might write that off as just getting broken in still, but after it sits for a few days the crank also feels really stiff when you roll it. And I mean stiff, like the engine sat with fuel in it for ahwile. Except I burn the fuel out of my engines at the end of the day and use after run oil. Once I get it fired the first time (which is a PITA 'cause it's so tight) it runs like a scalded dog, I don't have to reheat to start, and the crank frees up. Even at 2 day races it will fire up the 2nd day without heating the block. But once I shut it down for 4 or 5 days it will tighten up again. It holds a tune fine, and I don't see any fuel leaking from the front bearing and I don't feel any play in the rod. Wouldn't even be asking if it wasn't so dang hard to get it started after it sits for awhile. Anybody have any other ideas? I'm at a loss.

rageworks

iTrader: (47)

I have owned a few O.S.12TZ engines and never had
a stock rear bearing last over two gallons. Usualy they
start doing strange things, like you described. Then you
will notice a faint wizzing sound coming from the engine
after you rev it up. After that, if ran much more unchecked,
the bearing comes apart at high rpm's and turns the engine
into a nice paper weight. Slap a set of TKO ceramic bearings
in your engine and that TZ will burn many more trouble free
gallons of nitro.

cjtamu

iTrader: (11)

Yep. Fired it up today and the bearings are finally making that scratchy death rattle. Heard from someone else who had symptoms exactly like mine. Those engines were what, $200 each when they were new? SO all I need is $60 worth of bearings so they don't grenade on me? That's quality worth paying for right there LOL.

rageworks

iTrader: (47)

Check the lower con rod bushing too. The rod is under
alot of stress during break-in. So, if there is any play
in it at all, now is the time to replace it also. Don't feel
too bad about it. I have had the original bearings in O.S,
Novarossi based and Picco engines do the same shat.
Just because they have Swiss stamped on them doesn't
mean squat to me anymore.

Wildbillsphotos

iTrader: (31)

+1 on the TKO bearings

cjtamu

iTrader: (11)

I've had the bearing on one NR go out prematurely, but that was when I was sick at a race and someone else tuned it and overleaned the bottom. I ran the CV and CV-R for years and never had bearing problems. The TR was the first OS .12 engine I remember seeing consistent early bearing failures in. I have a TR in a box right now that I put new bearings in and will be going in the truck till I get the TZ's done LOL. But it seems to be a consistent problem with the TZ and with some of the big block OS engines also. It's a shame b/c the TZ is the best running .12 I've ever had, but I know I can buy a NR and put 6-8 gallons of fuel through it before I ever need to think about bearings.

BTW, rod feels fine, no play, but we'll see when I pull it out. All my engines are at 200+ deg the first time they hit pavement so the rod doesn't stress much during break in, but I'm worried about the stress this stupid bearing put on it.