Curious if the valves get looser or tighten with mileage? If they get tighter, then eventually you could pop the head off a valve. If looser, wouldn't it just "tick"....

Thanks in advance.

Mike

 

Valve clearances will get tighter as the seats and valves wear. As wear happens, the valve seats farther and farther into the seat, using up the valve "clearances"





Phil

 

Interesting... I always thought it was the other way around, valve clearances increased with wear. I have always thought that the cam lobes, rockers and valve stems wore faster than the seats.

 

Lobes, rockers, and valve stems, in a healthy motor, will have near zero wear.

The valves and seats are taking a beating at high rpm. The seats mushroom and the valve faces wear. Valves can "recess" quite a bit into seats in say a racing environment.





Phil

 

Depending on cam grind, if the valves are allowed to "hammer" back into their seat, the valve stems will stretch as well. IIRC, some cars will tighten, maybe a 911. But (again IIRC) a Mercedes Diesel will increase tolerance.
This is a good question, because some valve trains will tighten(bad), because they will eventually hold the valve open. This puts valve spring pressure on the cam/rocker and, more importantly, disallows the valve to cool as it rests in the seat/head(and leak compression). Others may open allowing the seat to sink heat and giving an audible clicking as the tolerance opens(good). A consistent tightening/loosening of valve lash upon adjustment over a period of time may give you an idea of whats happening.

 

Very interesting guys. Thanks for the clarification and the perspective from the other side of the wear pattern. Tightening would surely be a bad thing. I'm about to get into my first 911 adjustment on my 3.2, so we will see how it goes.

 

Ian, thats the best thing...stay on top of adjustments. I''ve heard a debate amongst Porsche techs weather to set the valves "loose" or "tight". Some may prefer "tight" to increase valve duration and performance, others choose loose to preserve the top-end. All this using the same feeler gauge.
Consistancy from one cylinder to the next is key, and regular maintenance.
Cam grind comes into play here. There are people who will "regrind" cams(BMW comes to mind) where they simply remove material from the bottom of the lobe. In the end this will increase duration and lift, but create extreme lateral load on the valve stem and increase valve opening/closing velocity. None of which is good for the long run.
911-S cams are a nice, big, round lobes, but include overlap(intake/exaust open at the same time) as a result, which does not play well with fuel injection or turbos.
On the other hand, some cam grinds(Web Cam comes to mind) will actually weld new material to an existing camshaft and then regrind a profile for a specific application.
I guess my point here is that maintenance is important. Playing with "performance" cams is a risk, and the factory had it all figured out back in the 70s. It is popular for people to "upgrade" cams in a 911, but the proven formula is usually an "S" cam or "E" cam or "964 grind", etc.

 

Nitpicking on ya..........but S cams worked quite well with fuel injection for six years (2.2 & 2.4S + 911/83 engines of '73 & '74 aka 2.7RS). Not even getting to the race car engines. But I get that you probably mean CIS/plenum intake electronic injection systems.

Anyway, over time some tighten, some loosen. Main thing is to stay on top of it. Of any of the swivel adjuster engines I've ever run, I can't say any have been .001 off come adjustment time. I'd usually screw with engines often enough that I personally never saw one of my track engines go too long without adjustment. Customer engines? Ugly truth is that there'd usually be a missed shift or some other "oops" in there necessitating repair work.

I'd love to hear from someone experienced with shim adjust rockers. I only worked on a couple of them, and I never needed to readjust spring height. And we'd rev the **** out of them.

 

http://obd1interface.com/valve-adjusting-screwdriver/

https://rennlist.com/forums/964-foru...ting-tool.html

 

My friend's 82 SC is a sort of test bed for 911 neglect and durability. I know that for many, it should be parted out and taken off the road. But for him, it's transportation. Anyway, I adjusted the valves last year, which had not been done for about 5 or 6 years. Some of the elephant's foot adjusters were a full turn and a half too tight. I bet the pistons were hitting the valves, and for sure they were not closing. That same car passed smog last year with unbelievable numbers. Less than 30 ppm HC, and almost no CO or NOX. Runs cleaner than mine, and his is a collection of different parts from different cars, literally.

 

[QUOTE=whalebird;8462639]Ian, thats the best thing...stay on top of adjustments. I''ve heard a debate amongst Porsche techs weather to set the valves "loose" or "tight". Some may prefer "tight" to increase valve duration and performance, others choose loose to preserve the top-end. All this using the same feeler gauge.

Loose, tight? Setting with a 4mm feeler gauge or a dial indicator is BS when saying loose or tight. It is like measuring to 3 or 4 decimal points with a 12 inch ruler. A tight slip fit is what the books say. Any tech who thinks he is more accurate (looser/tighter) with either of the gauges is dreaming.