P79 head mod

[Patcon]

Whats the total advance? You moght try backing it down a couple of degrees and see if the detonation goes away

[Reptoid Overlords]

Thanks for that. I was going to ask about it but you just answered it. I'll try backing it down a bit. Not sure about the total advance. I set it with a timing light until the light flashed right at the 10 degree mark on the crank indicator with a warm engine/vac advance plugged.

While you guys are here, I have another question.

Since I've re used my valve springs, I've been reading about people who have had a lash pad pop out after having their valve trains out.

I don't think this has happened to me, but since I'm pretty new at this, relatively speaking, I want to be prepared for any eventuality.

If I were to miss the initial popping out of a lash pad, what symptoms would I observe in a running engine that's had a lash pad pop out?

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[Jeff G 78]

1 hour ago, Patcon said:

Whats the total advance? You moght try backing it down a couple of degrees and see if the detonation goes away

According to the chart, he could have one of three 1980 distributors.  Total advance could be between 42° and 52°.  Chances are good though, it's 47°.

Distributor Type	Static Timing (BTDC)	Centrifugal Advance (Degrees)	Vacuum Advance (Degrees)	Total Advance (BTDC)	Engine Speed for Total Advance (RPM)	Full Throttle Advance at rated speed [No Vacuum](Degrees)	Transmission type  (Manual/ Auto)	Model Year (280ZX)	Country or special location/ designation
D606-52	17	12	11	40	2000	29	M
D609-56	10	18	15	43	2400	28	M
D609-56A	10	18	15	43	2400	28	M/A
D6F3-01	7	23	12	42	3200	30	M
D6F3-02	8	23	12	43	3200	31	A
D6F4-01	7	20	15	42	2720	27	M
D6F4-02	7	20	11	38	2720	27	A
D6F4-03	10	17	15	42	2500	27	M/A		California
D6K8-02	10	17	18	45	2500	27	M	1979
D6K8-03	10	17	10	37	2500	27	A	1979
D6K8-05	10	17	20	47	2500	27	M	1979
D6K8-06	10	17	15	42	2500	27	A	1979
D6K8-07	10	17	18	45	2500	27	M/A	1979	Canada
D6K8-22	10	17	30	57	2500	27	M/A	1980	California
D6K9-09	10	17	15	42	2500	27	A	1980
D6K9-14	10	17	20	47	2500	27	M	1980
D6K9-02	10	17	25	52	2500	27	M/A	1980	Canada
D6K80-03	8	17	30	55	2800	25	M/A	1981	Non-Turbo
D6K9-02	10	17	25	52	2500	27	M/A	1981	Canada  Non-Turbo
D6K81-01	8	17	30	55	2800	25	M/A	1982	Non-Turbo
D6K82-01	8	17	30	55	2800	25	M/A	1983	Non-Turbo

 

[Jeff G 78]

1 hour ago, Reptoid Overlords said:

If I were to miss the initial popping out of a lash pad, what symptoms would I observe in a running engine that's had a lash pad pop out?

I had a lash pad pop out during a race.  The engine was down on power and had an idle miss, but otherwise ran okay.  Unless it gets wedged somewhere - then it will make a LOT of noise and cause damage.  I simply popped the cover and put it back on in a matter of about a minute.  It was likely due to a n over-rev.

[Reptoid Overlords]

I had a lash pad pop out during a race.  The engine was down on power and had an idle miss, but otherwise ran okay.  Unless it gets wedged somewhere - then it will make a LOT of noise and cause damage.  I simply popped the cover and put it back on in a matter of about a minute.  It was likely due to a n over-rev.

That info is greatly appreciated. When I get home from work I will research the correct way to set total advance with my timing gun. My initial timing set was to the bottom of the stock spec. My thinking was that since the rise in compression, the lowest number of 10 deg would be best. But again, I will redtard it a few degrees and see.

 

I'm getting a tiny bit of smoke at downshift and directly after accelerating from a downshift. none at idle and none under heavy load. It's not white, or really even all that blue. But I noticed it real bad when I first started the engine and I had the advance all the way up. It mostly went away after I set the timing to 10deg.

 

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[madkaw]

Get rid of the vacuum advance and dial in 18 degrees initial timing . Take it for a spin . 

[Reptoid Overlords]

Ok. I plugged the vac advance, warmed the engine up, and set base timing to 18 degrees at 750RPM idle.

 

I went for a good long drive and noticed less detonation. It felt like it pulled quite a bit better as well. Detonation will occur under heavy load, but requires less finesse of the pedal to avoid. Thank you very much for that advice.

 

As for that smoke I mentioned earlier, I observed it again during my initial road testing today. It is in fact blueish, indicating it's oil.

 

Today was the first day I really drove the car and let it get to a proper operating temperature. After about an hour of driving, I can no longer see any smoke.

 

Seems more prominent when it's cold. The bottom end has not been rebuilt. Only the head. I wonder if my valves or valve stem seals are having a rough time setting? I'm not sure if they take time to settle like rings do.

 

I ran a compression check just now while the engine was good and hot. The results are:

1: 178

2: 178

3: 180

4: 180

5: 180

6: 180

 

My harbor freight compression checker might be reading lower than actual numbers. It did with my old engine when checked alongside a Snap On checker. At any rate, the numbers are even and close, so I'm hoping the rings are ok.

 

Plugs had a bit of oil on them, but weren't anywhere close to being fouled.

 

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[madkaw]

Back off a degree at a time until you eliminate the detonation . Sounds like your valve guide seals need replaced . 

You can research on how to set limits on your vacuum advance . You want to able to limit its travel and then try using it again.  

Also a thought. I run a MSA header and noticed early on that the exhaust noise in the header sounds rattling, like detonation , but it’s not . I was always suspicious until one day I got my timing way off and I heard real detonation . I then knew that there was a difference and he previous rattle was from exhaust

[Captain Obvious]

I just rebuilt the upper end (just the upper end) of my broken cam motor and I'm getting the same blue smoke on deceleration that you are.

My first thought was that some of the valve seals had popped off or weren't seated properly. I did the ol' rope stuffed into the cylinder trick and pulled a couple of the springs back out to have a look and didn't find anything amiss. And since then, I've tried my best to visually verify that the rest of the seals are down where they're supposed to be. With limited success, I've confirmed that all the seals look like they're seated.

So, assuming that all the seals ARE seated properly, my second thought goes like this... Before the upper end rebuild, most of my valves were not sealing properly, and I'm theorizing now that I've done the upper end rebuild they are sealing much better. Better valves, higher vacuum, and I'm thinking that maybe I'm pulling more oil up past the rings than I was before.

I get a good puff of blue at the bottom after coasting down a big hill. Especially if the RPMs were above the fuel cut-off level. Then once the fuel starts spraying in again, all the oil which had built up in the cylinders (while the cylinders weren't firing at all) is all burned at once.

That, or maybe there's something wrong with the sealed power valve seals that I used. There was some discussion, by me, about that possibility in the past.

What valve stem seal brand did you use?

[Zed Head]

I like your oil ring theory.  I think that worn valve seals show up as smoke on a restart because the oil leaks down while the engine is off.

Oil scraper problems don't show up on a cylinder pressure test either.

[Reptoid Overlords]

I too am using Sealed Power valve stem seals.

 

The symptoms I have are almost identical to what you have described in your last post(quote button on my phone isn't working).

 

And would possibly explain good compression readings as Zed Head said.

 

I brought the car to work to mess with the distributor timing on the way home after work, and to keep an eye on that smoke. It's getting harder to see it as I continue to drive it. I have been able to detect it by simply looking in the rear view mirror to see the smoke following the exhaust air vector up to the rear window, then trailing as I drive off until it stops after a few seconds.

 

This morning I tried to look back there while driving in the dark with the headlights of the cars behind me to help notice smoke. Kind of a rude way of testing, but then again it might be what some drivers here deserve. I observe less smoke as the car warms up, and the more miles I put on it. I'm at about 50 miles since installing the engine.

 

 

 

 

[Reptoid Overlords]

So I settled in at 12 degrees initial timing with no vac advance to alleviate all detonation.

 

I will take the recommendation from[mention=6833]madkaw[/mention] and research modifying the vacuum advance. Thank you for suggesting it. You seem like a busy dude and I appreciate you taking the time to help.

Edit: I appreciate everyone's help[mention=19495]Captain[/mention] Obvious[mention=529]Zed[/mention] Head[mention=1660]Jeff[/mention] G 78

 

I noticed that before retarding timing, that the blueish smoke issue was concurrent with detonation pinging. I hadn't noticed it before somehow. Seems like the longer I run it, the less it smokes on post coasting acceleration.

 

After retarding the timing, I observed a drastic decrease in smoke. Not sure how it would be connected to ignition timing.

 

Maybe I'm too colorblind to tell the difference between types of smoke?

I've seen rich fuel smoke it's it's obviously black. This smoke has been blueish and very dry, if that makes any sense.

 

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