Datsun Roadster Forum-311s.org

The R16 in the '69 has probably got about 65000 miles on it. AFAIK, the head has never been off it.
I drove the car to Blue Lake a few weeks ago for the meet. All was well, and she ran great.
Three traffic lights from home, when I stopped at a red light, the car barely idled.
It ran ok above about 2500 or so but below, it was definitely running on three cylinders.
Got home and parked it while I sulked....
Earlier this week, I decided to do some checking and determined the intake valve on #3 was not closing (compressed air going into the spark plug leaked out the carb as qucikly as it went in).
Checked valve clearance and looked for issues but found none. No water in oil, no sign of water or oil on the spark plug. Plugs all fire well.
After a couple dammits, I pulled the head. Valves look good, not burned or pitted. No carbon buildup, in fact the head is very clean. Pistons show no dings or signs of a strike. Shine a flashlight into the intake port on #3 and I see light shining past about half the valve body. Popped the valve springs off that valve and the valve doesn't just drop out but a tap with a deadblow knocks it out. Valve lip is good with no nicks or scorches as is the seat. I put the valve back and it sticks about 3/4 way in. I can force it in but the stem is obviously bowed or it wouldn't be hanging up.
So, I chucked the valve in my three jaw drill press chuck and turn the drill on low speed. the valve wobbles. The farther down the stem I grip it, the worse the wobble.
So, the valve stem is bent. Question is, how?????
It would seem like a valve strike hard enough to bend the stem would leave a sign on the piston. I see none. Even after a nice wipe with WD40 to remove any soot or oil, the top of the piston is smooth with no nicks or dings. There's no sign of something being ingested into the cylinder and the car has always run with the stock air cleaner in place.
IThe valves are in good shape, there is little ridge in the cylinders so I'm tempted to simply replace the valve if the replacement slides smoothly thru the guide but I'd sure like to know what the heck happened.
I like a good mystery on PBS but not in an engine. Something happened but I have found no evidence of anything wrong other than a suddenly bent valve.
Any ideas?
Dan

Sounds like a slow valve symptom
Oil good and clean ?
It whacked slightly.
Old gas can do it gums up the stem.
Coolant full ? #3 ,is the hotest cyl.

QT here would price 91 octane same as reg. at 1 station ( they were trying to get rid of old gas ) the kia dealer I was at filled up the new cars . a week later many just cranked with 0 compression. I had a hard time convincing the SM. it was the gas.

Oil is clean, nearly new with less than 50 mile since last change. Castrol 10/40.
I suppose the gas which was about 1/4 tank or so, might be 30 days from pumping.
No sign of sludge on any of the valves tho.
Thanks
Dan

Hey Dan, I have a question, does the engine ever have "after run" as if it doesn't want to shut off. This is just a possible guess, I have heard that sometimes bent valves can happen when an engine acts up and keeps running on its own, especially if the engine kicks backwards when doing it.

Good question Bill. I don't recall this one running on.
It seems like if the valve were bent as a result of running on it would be apparent at next startup. Not in the midst of a drive.
Good thought tho, perhaps some weakness from prior, unnoticed damage chose that time to show up.
Anyone else have a guess?
Dan

Yes, as far as I know valves don't bend on there own, it had to have help from some where or at some time. Another thought would be if the valve could have possibly been bent during a valve seal R&R with a lever and hook type tool, and over time it ran but eventually seized on your return home from the show. Good luck with it.

Not familiar with the R16 but could rocker arm geometry cause side loading on the valve stem?

I don't see how Joe.
The rockers are shaft mounted so side loading would wear a sort of taper on the shaft. Rockers move freely with little to no visible wear.
Still, like Bill said, something bent that valve.
Dan

Is is possible that you over revved and floated the valves?

Sure but I don't remember revving the engine or missing a rushed shift.
It idled fine at the first 4 lights off the freeway. At that point the road is flat to my house so not even much of a load on the engine.
I haven't checked the head thickness so it may have been shaved. I'll measure in a few places and see.
Dan

My guess would be somehow the valve stuck in the guide a little for whatever reason and the piston hit it just enough to bend it slightly but not leave a mark. I would pop another valve and see how it feels in that guide and see if there is a tight spot. Valves and such expand when hot so if it has a little drag when cold it could be just snug enough when hot the valve spring can't close it. Also couldn't hurt to measure the stems of the 2 valves to see if there is a difference.

I'd say you likely had a minor valve float on an overrev or a tired spring. Guides typically get looser with miles. Make sure the spring is still in spec- it probably is, but might be on the "light side". With a 65k engine there will be plenty of carbon on the piston and that stuff is pretty durable, so you may have touched it an not left a noticeable mark. It only takes a kiss.

Thanks guys. I will slip in another spring and look for any drag or out of round.
I'll check the inner and outer spring heights too.
Will let yall know what I find.
Dan

All my larger than stock but with an 8mm stem (smaller than stock) intake valves were hitting the block, leaving a clear mark. None were bent, so maybe it has to do with how or the angle, i.e. the piston striking it.

This weekend I removed the valve and did some measuring.
Head is stock 3.248" thick and flat. No sign of leaking head gasket. Valve springs are within 1 mm of stock height (I think it's 48.4 mm from memory). I slid the rocker back against the spring on the shaft and there is no worn groove or galling on the shaft.
I have a couple other heads so pulled an intake valve and slid it into the guide on the head with the bent valve. There is no perceptible wiggle in the valve stem/valve guide nor can I turn the straight valve to a position where there is a perceptible increase in friction when opening and closing the valve.
I turned the engine off tdc and brought the #3 piston up and sure enough, there is a small ding where the valve hit it. I can just hook my fingernail in it so guessing it to be less than .010" deep. A closer look at the valve shows a spot on the valve head where the piston hit. So, for those who were sure the issue was a valve strike, you were right on target.
I slipped the bent valve into the other head and it dropped right in. Kinda strange because it would bind in the other guide. I found that if I turned it 90 degrees in either direction it would begin to hang up and turning it more would bind it tightly. I have not miced the stem to see if out of round but my guess is that the guide is worn a bit and if the bend is aligned with the wear areas of the guide bore, it will slip in but as the bent stem is turned in the oval bore, it binds in the narrow direction of the bore. Oddly, both heads have the same thing. Time to get out my mics and start measuring.
As I mentioned, I was at Blue Lake and the issue happened on the way home. I have two good pulls between Blue Lake Park and my home. 1 is going across the Columbia. It's uphill and a good 3500 to 4000 rpm to keep up with traffic. The second is going up a 4 lane street after getting off the Freeway. There two lights on that uphill grade and I stopped at both. No missed shifts but it's a good pull so I rev 3500 or so going uphill because a little inertia is lost at each shift and I don't want that big Dodge to run over me.
Now, the question is why.
I have not been able to measure any obvious fault (over cut head or collapsed valve springs, worn valve stem) so not seeing a reason for the strike.I don't know why the valve hit the piston and I'm afraid to simply replace the valve and button it up again since I have no reason to believe I've fixed anything.
Any ideas or suggestions? I can put the other head on the engine and should be fine but I will still not know what happened with the bent valve head so need to at least make a believeable guess.
Dan
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