Burnt Valve ? '78 620

[Sh00bs]

white smoke if left idling after warm up. comes and goes. has a little engine noise while driving, slight tick. 

im leaning towards a burnt valve. thoughts ? i checked for vac leaks and replaced all older/harder vac lines. it's originally a california truck, so there's a lot going on around the carb... 

i guess i'll start with taking the valve cover off, taking a look at the valves and maybe adjusting the valves ? if adjustable... i'll google that. L20b

[datzenmike]

Does it require topping up the coolant every week? White is usually explained as steam from a failed/failing head gasket. If coolant is going through the combustion chamber the rad will need topping up now and then. Have a look at the spark plugs. One that is noticeably whiter and cleaner than the others is another indication.

 

Constant ticking that does not get louder under load could be a loose valve setting. Loose is better than too tight but should be adjusted. Warm the engine thoroughly, (20 min or so) Intake 0.008" exhaust 0.010".  Two ways here....

 

1/ Bump engine till the cam lobe is NOT on the rocker arm. Make adjustment for intake or exhaust the move to the next valve. This is laborious and takes long enough that the engine may cool down.

 

2/ Set engine to TDC on #1 compression stroke and set the following valves... both valves on #1 cylinder, intake on #2, exhaust on #3. Turn ONE revolution to TDC set exhaust on #2, intake on #3 and both valves on #4 done. Very fast and no bumping of the starter.

[wayno]

I burnt an intake valve once over 300 miles from home, it started back firing thru the carb, I had to get home so I removed the spark plug wire from the bad cylinder and drove home on 3 cylinders, it was gutless but it got me home.

I expect if it had been an exhaust valve it would have just missed, but it may have back fired thru the exhaust, I had a exhaust valve go tight on my in my work truck 4 or 5 years ago and all it did was miss, I was close to home(within 2 miles) so I drove it home and fixed it without any continuing issues.

 

You do not want un-burnt fuel going into your exhaust so if you have a bad exhaust valve and it is just missing you should still remove the spark plug from that cylinder, otherwise bad stuff can happen like this.

 

But I fixed it and it looks like this to this day, the explosion was indescribable.

 

 

[bottomwatcher]

Damn dude, I thought I was a cheapskate. I would have just let that muffler go. Way to stick with it Wayno.

[datzenmike]

17 hours ago, wayno said:

 

 

But I fixed it and it looks like this to this day, the explosion was indescribable.

 

 

 

 

wayno I had trouble starting a '62 chev and the exhaust ran diagonally under the drivers seat. I had the window down. It caught and boom! split it lengthwise and bent the floor up. My ears rang all that light.

[Sh00bs]

nope coolant is good! 
i'll work on setting the valves this weekend. i know these trucks arent fast but mine is like samurai slow... if you've ever driven a stock samurai, you know what i mean. i feel like with 110hp, now maybe 80 ? it should still have a little bit of pickup - ha no pun intended

[banzai510(hainz)]

well pull the sparkplug on what you think is the bad cylinder and see if it dont change. then do it to another cylinder and changes alot then you know the one you suspect is bad as you got no compression and running on 3 cylinders.

L20s go pretty good. No they not a Samurai  But you should know what it felt like when it was good.

[datzenmike]

My 710 is rated at 110 hp but this is gross engine power without alternator or accessories and driven off the crankshaft. Later this was measuring method changed changed to Net HP and read at the wheels, a much more representative number. More like 93 HP.

[Sh00bs]

33 minutes ago, banzai510(hainz) said:

well pull the sparkplug on what you think is the bad cylinder and see if it dont change. then do it to another cylinder and changes alot then you know the one you suspect is bad as you got no compression and running on 3 cylinders.

L20s go pretty good. No they not a Samurai  But you should know what it felt like when it was good.

true. i'll start pulling wires today and see if anything changes. haha wouldnt it be funny if ive been driving around on 3cyl thinking it was at full power

[banzai510(hainz)]

well I was upset you said Power of a Samurai... I know what that is. A friend had one and I was like FUCK this thing is slow

L20s are not that bad so its bad timing or soemething like that. Maybe a lash pad fell off a valve up 3 cylinders would be obvios I would think. or a tight rocker arm

[Sh00bs]

1 hour ago, banzai510(hainz) said:

well I was upset you said Power of a Samurai... I know what that is. A friend had one and I was like FUCK this thing is slow

L20s are not that bad so its bad timing or soemething like that. Maybe a lash pad fell off a valve up 3 cylinders would be obvios I would think. or a tight rocker arm

yeah we're barely above that. it's an EFI samurai though so a little better than a carb model lol but still very slow. and this is a tad more than that. 
on stock gearing and wheels, since i dont have an RPM gauge could anyone tell me what the engine revs out to ? and maybe an appx of redline in each gear ? 

[banzai510(hainz)]

I dont have a Tach in any of my datsuns.  but on a L20  6500- 7000 is reaching its power band in 1st gear  little less in the rest of the gears. Really I dont think it matters you just know when to shift before the valave float and loose power

[Sh00bs]

SO it's cyl #2
nothing changed when i pulled the plug wire. it was very noticable on # 1, 3 and 4. i first swapped

i pulled the plug, had what looked like rubber between the electrode and the the grounding rod on the plug. weird. new plug in (.034), still nothing... so i pulled the wire off the dizzy side, got shocked lol so i have spark at the dizzy. swapped wires, still nothing...
i compression tested (hot) cyl 1, 102psi. then 2.... 0 psi. absoluelty nothing
3 was 105 and 4 was 101.

so im thinking stuck/burnt valve. about to pull it in the garage and pull the valve cover off to have a look. i'll post a pic on Imgur with what i find and link it.

[banzai510(hainz)]

valve lash pad fell off I think! or tight rocker arm

[wayno]

On 4/27/2021 at 3:41 PM, bottomwatcher said:

Damn dude, I thought I was a cheapskate. I would have just let that muffler go. Way to stick with it Wayno.

 

That muffler was only a few years old, the metal was good so I used a couple hose clamps and made it round again and welded it back together, it is not pretty but it does the job it was designed to do ugly as it is, it is under the truck and no one would even know what it looks like except I posted a photo of it here. :lol:

[datzenmike]

wayno I've pulled old pipes and mufflers off old trucks and put them on mine for the cost of a clamp. Quiet is quiet same as a $350 job. Had the time but not the money to spend.

 

1 hour ago, Sh00bs said:

 

so im thinking stuck/burnt valve. about to pull it in the garage and pull the valve cover off to have a look. i'll post a pic on Imgur with what i find and link it.

 

 

Check exhaust valve isn't held open by no valve clearance first. Or has sunk up into the head and no clearances. Is it making any noise? Seat may have fallen out of the head.

[banzai510(hainz)]

most times the lashpad fell out and if you catch it soon enough its near the valve spring before it fells in front or behind the head into oil pan

[Sh00bs]

Welp. Check this out... better than needing rings I suppose

 

 

[Sh00bs]

Got the rocker back on 

Valves adjusted, oil was a little low... added some 

She runs WAY better now, but its got a mean tick that comes and goes. Tried adjusting again, made a few small adjustments... same thing 

Gonna let completely cool down and go back tomorrow to set valves cold. See what happens

 

[datzenmike]

Set them hot. Cold is ok if assembling the head as a starting point. Hot is what they run at and cold assumes they will expand to the correct clearance.

 

 

[banzai510(hainz)]

make sure the lash pad didnt fall out

 

I dial the rocker post down then put the rocker back on then adjust per spec.

[Sh00bs]

She fell out but I put another one on with a new (used) rocker that wasn't damaged. The one that came off was slightly damaged... so I wanted to replace it

The cam lobe got damaged too, but not as bad as the rocker. Thinking the damaged cam could be making the noise? Good excuse to toss a performance cam in there 

 

Only got pics of the rocker... but I can get pics of the cam easily 

 

[banzai510(hainz)]

run 15-40 20-50 oil see if that helps

[Sh00bs]

the tick that comes and goes has me puzzled
part of me thinks it's 10fold the slightly damaged cam lobe.... but then i think if that was it, it would be doing it all the time? good thing the weather is warming up, i have 2 bikes and my Jimny to daily in the mean time 

[datzenmike]

As long as there is no sharp edge on lobe or pad it should ride on the flats fine. Certainly long enough to be replaced.

 

Random ticking... see if the engine is hot or cold when it occurs or anything that makes it NOT random. Could it be exhaust? popping through a crack in the manifold or pipe joint?

 

Yes Shell Rotella T4 15w40. Thick enough for California weather and high in ZDDP to protect your cam and rockers.