Valve Adjustment Question

rrnixonjr · 12-09-2007, 04:02 PM

Is it normal to do a valve adjustment and find almost every clearance too tight?
Maybe two valves were loose, and probably making a racket.

burgermeister · burgermeister's Garage

I only have 1 reference point ... I'd say most of them were just fine, only a few needed slight tweaking. Of course, I bollocksed them all up first time through, and about half ended up too loose (apparently I thought they were too tight). For the second adjustment 1 week later, they were mostly loose ...

Backside method worked for me.

rrnixonjr · 12-09-2007, 04:08 PM

I double checked my clearance using the back side method. Used the .0025 go, .0030 no go. Just a slight rock in the rocker for clearance. Guess I will see when it's finished.

john walker's workshop · 12-09-2007, 04:25 PM

easy to think they're all too tight if you're not familiar with doing it. then you spend lots of time trying to adjust and they all end up noisy when it's all buttoneed up. but yes, occasionally you find an engine with lots of tight valves.

rrnixonjr · 12-09-2007, 07:14 PM

Thanks, guess I will have to button it up and see. Have to trust the gauge at some point.

GrantG · GrantG's Garage

Mine seemed to all be a bit tight when I checked them and were quiet when I did the backside adjusting method (loosened most of them) and buttoned it up - car ran great! Steve W. at Rennsport said it's common for the valves to tighten with use on the 911 (counterintuitive).

LakeCleElum · 12-09-2007, 08:36 PM

Mine were all tight when I checked mine the first time. I think the PO had neglected them for some time. My experience is mainly with motorcycles, but most of the valves I've ever adjusted were on the tight side, not loose....

burgermeister · burgermeister's Garage

Interesting ... the only way I can think of that valves would get tight is if the valve face / seat wears. I can't imagine the rocker / cam wearing enough to require valve adjustment - seems there would be little left after 150K miles, and it would make the valves loose. I always wondered why the adjustment interval was so frequent...

So, is it wear on the valves & seats that's the culprit?

Dixie · Dixie's Garage

It's easy to find out for sure if they're too tight. Check them using the "backside method". A search will bring up oodles of info.

rrnixonjr · 12-10-2007, 04:24 PM

Thanks for the input, I will check clearances one more time before buttoning up. I don't mind the work, the experience helps and fortunately the car is not a daily driver.

Hard-Deck · 12-10-2007, 06:04 PM

I used the backside method after checking all the clearances. The PO, or his mechanic had EVERY valve on the tight side.

old man neri · 12-10-2007, 06:38 PM

Mine were almost all tight when I did my first.

Ole Petter · 12-12-2007, 01:07 AM

HI...

I hade my valved adjusted after I bought my car. All the clearances were spot on.

The engine is a 2.7S. It is recommended to adjust the valves at intervals of 6.000 miles.

I have had Volvos (Turbo) for 14 years now. They have valve adjustment by shims. Many Volvo-mechanichs says it is not neccessary to adjust them after they are run in. When I requested an ajustment of my former Volvo at 120.000 miles service, the Garage said: "Nah, we don't usually do that". I insisted, and they did the job, but it turned out that all was great - as they told me...

Is is really neccessary to adjust the valves of a run in Porsche 911 engine ever so often? I would think the valves would get more open over time, and be more rappety/tappety noicy and that would indicate time for adjustment? And isn't a tappety engine an happy engine? If things get too thight, then there would be cause for consern?

Ole

psalt · 12-12-2007, 04:43 AM

Ole wrote,

I have had Volvos (Turbo) for 14 years now. They have valve adjustment by shims. Many Volvo-mechanichs says it is not neccessary to adjust them after they are run in. When I requested an ajustment of my former Volvo at 120.000 miles service, the Garage said: "Nah, we don't usually do that". I insisted, and they did the job, but it turned out that all was great - as they told me...

Is is really neccessary to adjust the valves of a run in Porsche 911 engine ever so often? I would think the valves would get more open over time, and be more rappety/tappety noicy and that would indicate time for adjustment? And isn't a tappety engine an happy engine? If things get too thight, then there would be cause for consern?

Hello Ole,

Like many things, there are several "old wives tales" about valve clearances that are not true. The idea that valves become noisy over time and just need to be adjusted to quiet down is usually false. The normal wear pattern is for the clearance to tighten up over time, as the valve seat abrades in a process of oxidation and material transfer. Valve noise is usually wear in the guides, stems, tappets or rockers. It is a bad idea to chase noise with tighter clearances and a bad idea to reduce the spec under the notion that they will "loosen up" over time. Another misnomer is that valve clearance tighten up on a hot engine. On many engines, 911's and shim and bucket valves, the clearances get wider with heat. Try measuring the clearances on a hot engine. The valve clearance spec is not there to allow for thermal expansion. The clearance is there to allow sufficient time for the exhaust valve to sit down and give off heat. The clearance an mfg choses is a balance of heat rejection and acceptable noise, considering the use of the engine. The 911 spec is very tight, the intended use is high, and therefore it requires a shorter inspection interval to avoid burned exhaust valves.
The requirement is to inspect, not to adjust.

Gunter · Gunter's Garage

Ole:
The Volvo has hydraulic lifters and the clearance is adjusted with special washers like you say.
The B21 with OHC is quite incredible.
I have 300.000 km on it and adjusted the valves only twice.
Most 911-engines don't have hydraulic lifters, they are considered flat-tappets and need to be adjusted more often.

jjrowe · 12-12-2007, 08:43 AM

Since we are on the topic ... I was wondering about the inspection interval. I have heard Wayne and others recommend 6,000 mile intervals for the 2.7. My owners manual says 10,000. Is there a difference between 2.7 engines or is the 6,000 interval something that people that worked on the cars came up with?

Jesse
76' 911S

Gunter · Gunter's Garage

Jesse:
Whatever makes you feel good; 6 or 10k. I go more than that at times.
On 2.7 engines, I would recommend that you check the head studs with a calibrated torque wrench whenever you adjust the valves.
The magnesium case of the 2.7 has more issues with studs pulling out than the later Alu cases.
A good routine is to do it when changing oil:
Drain all oil, open the valve covers, check/adjust the valves, use a 3/8" drive torque wrench set to 23-24 ft-lbs and with a long 10 mm Allen check the studs.
You can make a tool by getting a LONG 10 mm Allen key, cut off the short end, then put the long end into a 10 mm socket on the torque wrench.

gigem75 · 12-12-2007, 10:02 AM

Purely speculation here but I doubt under normal wear conditions you would have a valve adjustment go out because of wear on the valve seat, valve, cam, or rocker. I would suspect what happens is the threaded adjuster or nut might stretch or even the valve stem itself? With air cooled engines the thermal expansion/contraction of the parts in the valve train most likely contribute to the need for periodic adjustment??????

rrnixonjr · 01-19-2008, 03:41 PM

I want to thank everyone who helped me with advice on my valve adjustment. Finally closed it up and it ran like a top. Smooth and sounded like a sewing machine, loud valve noise gone. That might have been from rocker arm moving almost out of its housing. Still, it's gone and sounds good. What a nerve racking job the first time. I got so I could rock the rocker arm and know if it was too loose.