nisileighty

Having an interesting issue with my SR, its a s13 redtop. A couple of nights ago I managed to shatter the exhaust rocker arm on cylinder 4. I replaced the rocker arm with a new one and reassembled everything. When I started it back up, it ran like shit and after unplugging coil packs I found that it was only running on cylinders 2 and 4 (the one with the rocker I replaced). Cylinders 1 and 3 when unplugged did not affect the motors running.

I checked compression and I had 155 psi on cylinders 2 and 4, but literally 0 psi on cylinders 1 and 3.

When I crank the engine by hand, there’s no noise or resistance of a piston contacting a valve, however the starter has a hard time cranking the engine as it’s cranking noticeably slower and less smooth than before.

I’ve checked mechanical timing once, and I’m typing this as I’m doing it again to be sure, but I’m stumped and if there’s any input about this that’d be greatly appreciated. Thanks!

[240sx]

I don't suppose you have a leak down tester, do you?

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TheRealSy90

Hate to break it to you but sounds like the timing was off and bent some valves possibly.

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jedi03

+1 on bent valves...how did the rocker shatter?

TheRealSy90

Also the dead cylinders could have gotten bent valves when the rocker broke, not that you assembled anything wrong when you fixed the rocker.

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nisileighty

So when the rocker breaks, can that somehow throw the timing off? I was under the assumption that on the cylinder the rocker breaks, the valves will immediately close. As for the other cylinders, I couldn’t think of a reason that one missing rocker would cause the timing to be thrown off enough to contact a valve.

The rocker shattered under hard driving/high rpms. Tapped the limiter once and it went. It’s an ignition cut at 7k, and I’ve never spent much time on the limiter, a tap or two at the most in second when I drive the car hard which isn’t often.

TheRealSy90

It really shouldn't have. Signs are leading to the mechanical timing being off when you initially cranked it after the repair. The starter has enough torque to bend the valves if they contact.

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KiDyNomiTe

Timing can be off from your reassembly process, I've done it before

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nisileighty

Alright, that’s definitely a possibility. I’ll get the cylinder head pulled today and let you guys know. Thanks!

nisileighty

Here’s a pic of the rocker. If anyone is interested lol.

TheRealSy90

I just wanna say if you have rocker arm stoppers go ahead and remove them now. And look into doing dual rocker guides.

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nisileighty

Never believed in rocker arm stoppers actually helping so I never installed them. I also plan on doing the dual guide conversion.

snafupossum

Did you over rev the engine? Like accidentally shift into 2nd instead of 4th on the freeway? Sounds to me like the engine spun too fast causing that rocker to break and make others valves kiss pistons?

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nisileighty

Nope, literally turned out of my neighborhood and got on it in second from 25ish mph until redline. Kissed the limiter once and took a shit. Ran and idled funky and there was a super loud tick. Pulled the valve cover and the rocker was just sitting in two pieces.

slider2828

Is it this easy?



Do you just grind outter side of the arm?

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nisileighty

nisileighty

No signs of piston/valve contact.

s13silvia123

thats no way to tell if the valves are bent or not. there's a your video on how to tell if they are leaking or bent.

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RalliartRsX

Pour some acetone or similar and see if it leaks out. If it does, valves are bent. Unless bent significantly, the naked eye cannot tell if the valve is sealing or not.

jedi03

also put spark plugs back in or will leak real fast lol, additionally what is between the valves in your first pic of the head?

RalliartRsX

^^ Looks like oil and carbon.

nisileighty

I dropped the head off today at a machine shop to have it vacuum bench tested and waiting on the results.
Between the valves was just a bunch of flaking carbon and some spilt oil from when I turned the head over.

Nysil Via

your pistons look way cleaner than mine. I put a scope into my spark plug hole and snapped some pics.

nisileighty

My bottom end was rebuilt about 2k miles ago which is why the pistons are so clean. All the built up carbon wiped off with alcohol.

Kingtal0n

I run a fuel cut rev limiter soft 6400rpm for daily driver oem sr20det engines

it won't do this if the head is right at 6400-6600

Ask yourself if you really need that last 500rpm, if not, ditch it for the increased reliability

nisileighty

I’ll definitely lower the limit a few hundred revs. It’s an ignition cut which I believe was the main reason the rocker broke.

Kingtal0n

oh yeah. We see that all the time. Its rare to have a rocker failure at 7k on the fuel cut limiter, it would have surprised me.

What happens on the ignition cut is some fuel explodes in the exhaust system, which creates a high pressure between turbine and head, pops the exhaust valve open if a spring is weak enough.
The valve then being open when it isn't supposed to be is now 'in the way' when the cam comes around, rocker loses its 'grip' and cam cuts it in half more or less. might leave a huge gouge in the cam lobe too. It basically jams sideways in there till it fractures like a brittle chalk, often sending little shims and guides into the oil pan if ur lucky hah.
If not, you never find them ;D

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TheRealSy90

Ignition cut is a no-no on stock valvetrain. I ran my old sr almost 8 years raping the stock 7,500rpm limiter and never popped a rocker lol.

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RalliartRsX

The is more the constant laying on the limiter vs just touching it prior to switching gears.

Drift cars and the like is a perfect example. On all my SRs, reving to 7-7500 RPM track day cars (300-360+ WHP) and touching the limiter (and just so on most shifts unless short shifting) I have yet to break a rocker or spit out a shim. This is with Spark Cut limiter (hard cut) and progressively cuting each cylinder in 100 RPM increments until redline (so cylinder 1 cuts @ 7100, cyl 2 @ 7200, and so on). This is very similar to a stock SR ecu logic. Never an issue.

The only folks I really se spitting shims are ones which lay on the limiter.

TheRealSy90

Yeah I layed mine on limiter for seconds at a time so idk haha.

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