What causes broken rockers?

89turbocabmike · 08-26-2007, 11:29 PM

I'm working on a friend's newly acquired 1.7 with an unknown history. It was parked in '91 due to an engine "problem". We had it towed to my garage and upon removing the valve covers found broken intake rockers on #2 and #3. The broken peices show no apparent flaws. Any thoughts on causes?

BURN-BROS · 08-27-2007, 05:37 AM

The valves probably touched the pistons either during an overrev. Check for bent valves with a cylinder leakdown test.

RandyLok · 04:27 PM

Is the type 4 an interference engine? I thought it wasn't.

BURN-BROS · 08-27-2007, 01:59 PM

Then I have no clue.....anybody?

Tobra · Tobra's Garage

not an interference motor by design, but if you dropped a valve seat I suspect you would see some interference

RandyLok · 04:35 PM

Well, yes, that's another scenario. Valve interference != dropped-seat interference.

John Rogers · 08-27-2007, 06:10 PM

What happens if you turn the engine by hand? How do the rockers and springs for the other two cylinders appear?

89turbocabmike · 08-27-2007, 11:11 PM

Engine turns over just fine. I didn't particularly notice that the valve tips on the affected cylinders were sitting at any different height than they should.

I've been giving this some thought through out the day since I will probably be the one rebuilding the engine. I'm worried of the possible hidden damage to the other rockers. A possible senario has come to my mind. The car was parked in 1991 due to some un-remembered problem with 94K on the odo. I found in the rear trunk, a receipt for a new battery in 2004 (which is installed and still looks like new) a replacement clutch cable and throttle cable, a couple porsche mags from that year as well as a mail-order P-car catalog(they who shall not be named). I wonder if perhaps someone tried then to resurrect this car and cranked over the engine and those two valves were seized and snapped the rockers. In hindsight, when I was looking at the edges of the broken tips for metal defects, they seemed fresh and free of any oil. However you can see from the pics that even the valve covers look pretty dry. I will do some more investigating tomorrow and hopefully get the go ahead to drop the motor

Thanks for all the replys!

NOTASIX · 08-28-2007, 08:09 AM

TIV rockers are VERY HARD TO BREAK!!!! I have only broken one in my lifteime of working with these engines..

A seized valve is generally the cause. Check the pushrods on those cylinders as well, if it was bad enough to break the rockers it was bad enough to bend the PR as well.

Seized valves usually occur on the intake, usually from an older engine that has dead fuel in the tank that literally glues the valve into the giude.. I'll bet you 50 bucks thats what happened with this engine-seen it a million times..