Internets_Ninja

I've pulled the intake on my 2015 C7 and 2017 Camaro SS. Guess what? The valves looked fine. Needing a catch can on a stock or bolt on LT1 is rubbish.

Steve_R

owc6

Is coking an actual problem? I don't think so.

I can tell you all that at 80,000 miles (few of you will ever see such milage on yours, BTW), mine broke a valve spring, and there was no evidence of coking. "Clean as a whistle" is what they said.

Steve_R

PatternDayTrader

Lol not exactly.
You don't see the valve head if you are just changing the spring.

owc6

Expound, please.

PatternDayTrader

Replacing a valve spring consists of removing the spark plug, then forcing compressed air into the cylinder (usually using a compression gauge hose) so air pressure holds the valve against its seat, then compressing the spring with a spring compressor (looks sort of like a miniature gear puller sort of), then you remove the valve keepers and the spring retainer, then you put it back together with a new spring. Its an easy job. The valve never comes out of the head. You don't even pull the intake manifold.

PatternDayTrader

Obviously if the keepers come out and the valve drops into the cylinder then that's major engine failure, which is something totally different.

owc6

PDT, so what you are saying is that when they replaced my valve spring, they never even had a chance to look at the back side of my valves?

PatternDayTrader

Correct.

I suppose if thy were stupid, then maybe they pulled the head off the engine, and made tons of work for themselves, and made your bill at least six or seven times higher than it should have been. Its not impossible. There's a lot of stupid people in the auto service industry.

Steve_R

owc6

OK, can you explain how the repair was done?

PatternDayTrader

Under normal circumstances that wouldn't happen. The reason why, is that if the valve hits the piston but doesn't actually drop into the cylinder, then when apply compressed air into the cylinder, you will here it leak back into the intake manifold because the valve wont seal properly. Usually it will be bent if it actually hits the piston. So what this means is you don't need to inspect anything, provided the valve still seals properly, and if it doesn't then you know immediately.

Don't get me wrong on this. Valve coking is a non issue, unless you have a mostly worn out engine to start with.

Steve_R

PatternDayTrader

No there's not.
I would guess that when he was asked the question, he probably thought he was being asked how clean the engine was under the valve over, because you do take the valve cover off.

PatternDayTrader

Where's your bill ?
Was it a few hundreds ? or was it thousands ..

owc6

$0.

Covered under Drive Train Warranty.

'14.

But anyway, how was this repair performed, then?

Maxie2U

PatternDayTrader

Well I cant explain what was done in your exact situation, but in post 27# I described how valve springs are typically changed.
Basically you pressurize the cylinder so the valve stays in place, then you remove the keepers and the retainer, then the spring, then reassemble with the new parts.
Under normal circumstances, the entire set of 16 springs can be changed in two hours or so, maybe three.

At no time do you see the valve head. Only the valve stem is exposed under the valve cover. Which is an interesting point about valve coking, if the stem is sloppy in the valve guide, then oil will be sucked into the intake port (in very small amounts), surface tension will keep the oil in contact with the stem in the intake port, and as the valve moves up and down, this oil is scraped onto the valve head, or just above the valve head. Eventually this will turn into the coking problem. So a catch can wont help, because crankcase ventilation is not where the coked oil comes from.

Maxie2U