help, please ! engine mechanical inestability (mainly at iddle)

[deQuincey]

hello

I anticipate possible problems by my side to communicate this correctly, my appologies for that.

my car is becoming a long step-by-step project towards perfection, at the begining big issues had been tackled, and now we are approaching something similar to and "end" (if it is sensible to say this kind of cars could have an "end" phase )

three months ago the car arrived to a good performing stage with nice and stable iddle, correct temperature, and so on, ….when, unfortunately, a valve broke out

so I have to had my cylinder head mechanical elements renewed and re-adjusted, those included: camshaft (it is silly but in the process it was broken), rocker shafts, springs, circlips, valves, stem seals, valve springs, ..., cylinder head gasket and bolts also renewed…

that operation meant also distributor dissasembly and reasembly of course, together with many other elements that were touched but not renewed

then also cooling liquid and oil (castrol classic 20w50) + filter oil was changed

now the car runs so-so, the temperature is good, it seems to have a little lack of power, and..... this !:

the iddle is at 950rpm, but it is not smooth, some little disrupted explosions occur (instead of a fine sequence of explosions that in their continuity would seem not to be formed by explosions but a continuous roar), you can feel those explosions in the form of pressure waves if you put your hand in the exhaust

moreover the engine itself as a "phisic body" (may be I will call it better a "solid"), vibrates a bit (enough to spill the water of a topped glass seated on top of the air filter container)

this irregular vibration had never occured in the past, and is more intensive at iddle and decreases with increasing revs

when you drive you can feel that lack of power and the little explosions will bother you now and then depending on revs and gear (I do not have an historic report on this by the moment)

so, what are your ideas ? what dou you think that is happening ?

I can not check the carbs syncronisation, but I feel that such a visible inestabili¡ty could not come from that, do you agree ?

I have the impression that the engine might be running on 5 cylinders, you too ?, ok how can I check this ?

and one step forward, what can be the cause ? distributor, rotor, spark cables, ….

(by the way. the distributor cap, rotor, and cables were changed some months ago, previous to the appearance of the broken valve, the only thing I am missing is a possible bad reassembly)

please, please, please help me, I am so tired ! I want her just to be fine for the last few sunny days before winter came !

thanks in advance

 

[61porsche]

Idle not stabile

Let's see....

1. New upper end- usually the valves are set a little loose( 14 vs. 12) in order for them to seat during the break in.... if it's been a little while adjust them at least twice carefully. Did you change rockers or eccentrics with a new cam? Sometimes it is also best to check clearance at the cam and heel of the arm- 8mm as a second way of guaging clearance. While there confirm the timing , cam position at TDC is correct. Lines up properly. ( Cam gear bolt to boss on top of bearing.) Timing and overlap- if timing is off one way or the other the intake impulses ( fuel mixture) gets more into either the intake or exhaust. This causes the "popping" which can also means mixture problems not optimum. Popping can be either carbs or exhaust and usually means lean if carbs and rich if exhaust.

2. Plugs and not firing on all cylinders- examine the plugs after you've gone out and run but not while sitting idle.- too clean of a new plug means its not firing along with dark or wet plugs- too rich. Since there are two carbs pay attention to the bank of cylinders- 1,2,3 and 4,5,6. Also , the difference at the ends since the mixture has to turn a bit as a design compromise. The relationship is important as you want them to be as close as possible for smooth running. Sometimes it's almost magical when a small turn of the screw turns on the cylinder that's missing or not quite firing as hard.

3. Carbs- at idle- it's likely one is too rich and not enough air is coming in as popping at the exhaust means rich. Since the fuel idle jet is fixed, adjust the butterfly to open slightly more. A tach and a vacumn guage helps as a visual indicator, but many can do it by ear - it will sound better. I also suggest you write things down as you adjust to see what adjustment works best. For the vacum guage- you can see a change of 1-3 in. and the needle stabilize more. If you use the tach- you'll see the increase and decrease- by writing it down on how much you turned the screw- you know where the halfway is and things get to very small adjustments.

4. Sync- a length of vacumn hose works to get close by listening to air coming in the carb. Always adjust the carb with more noise or hissing halfway and then the other upwards to match. Yes, it really matters for the smooth idle and power.

Again, you're trying to get the two cylinder banks firing as close to equal which causes the rough running with adjustments. Since I know it's hard for some to tune by ear; I also pick something that's vibrating and watch it as adjustments are made.

If running points- always check them before tuning.

Can you explain more about the broken cam and valve? Bad bearings? Loss of oil? Discolored because of heat? Which valve? Oil sprayer came loose?

 

[Lorenzo]

OT... but I'm astonished by the technical knowledge of 61Porsche, He always gives precious advices.
If it happens You ever come to visit Italy I'll be happy to exchange your consultation for the tune up of my CSLs with a dinner in the best restaurant in Bologna!:mrgreen:

 

[deQuincey]

Can you explain more about the broken cam and valve? Bad bearings? Loss of oil? Discolored because of heat? Which valve? Oil sprayer came loose?

hello, thanks as always for your detailed and good advises, I will go through them as soon as possible (perhaps this weekend), but first, to complete the information let me answer you those questions:

broken valve came first, it was during normal functioning of the car, i was going uphill, in third gear, at 3000 rpm´s, the car was performing well, and suddenly it lost power dramatically, a tiny "click" sound, and i was doing the last three kilometers to my house as slow as a turtle, diagnosis: one exhaust valve was broken (a 5x5mm bit disappear), see pic

the camshaft was broken during assembly, so no conection with oiling problems, or other fuction issues

regards

 

[61porsche]

Italy

Lorenzo,

Yes, we must get together.

I do business with Snaidero and Pinnafarina so my other dear friends have been trying desperately to convert me to a prancing horse believer over my air cooled tendency (although they mostly admit to owning German as well) with a side trip to Modena. I think though that they enjoy the difference!

Maybe we can get some other E9 members to join in? Oh well, yes when I come I shall let you know.

Thank you for the kind words.

 

[61porsche]

valve failure

Most often exhaust valves tend to color tan or off white similar to spark plugs. it looks like deposits caused the problem. What happens is that 25% of the cooling takes place at the valve seat and 25% takes place at the guide. It is likely, the lack of cooling of the valve head at the seat failed.

I would not suspect an oiling system problem. With new valves, springs, etc. you should be good.

It is also perhaps little known that 1 in five valve faillures are manufacturing defects so inspect carefully for any minor scratch, etc. during assembly.

Cam removal in M30s is tricky as the valves are in tension from the cam.

 

[deQuincey]

as i re-read the answer i found a question without answer:

Did you change rockers or eccentrics with a new cam?, ....the rockers no, but the eccentrics yes, they are new

Let's see....

1. New upper end- usually the valves are set a little loose( 14 vs. 12) in order for them to seat during the break in.... if it's been a little while adjust them at least twice carefully. Did you change rockers or eccentrics with a new cam? Sometimes it is also best to check clearance at the cam and heel of the arm- 8mm as a second way of guaging clearance. While there confirm the timing , cam position at TDC is correct. Lines up properly. ( Cam gear bolt to boss on top of bearing.) Timing and overlap- if timing is off one way or the other the intake impulses ( fuel mixture) gets more into either the intake or exhaust. This causes the "popping" which can also means mixture problems not optimum. Popping can be either carbs or exhaust and usually means lean if carbs and rich if exhaust.

QUOTE]