l18 compression test

[sanyantho]

Hi Ratsun,

      I have a 74 620 with a stock L18 and weber 32/36. I did a compression test on the L18 and got 130 for #1, 140 for #2, 130 for #3, and 140 for #4. Are those number ok?

 

Thanks in advance for your help...

[Draker]

They are low.. but it would probably run.

 

Was the motor hot and did you block the throttle plate wide open?

[datzenmike]

Low but most important that there are closely the same and within 10% of each other and hopefully you are not excessively burning oil. 

[sanyantho]

They are low.. but it would probably run.

 

Was the motor hot and did you block the throttle plate wide open?

The motor was hot, but I did not block the throttle plate open. Would that make a noticeable difference?

[sanyantho]

Low but most important that there are closely the same and within 10% of each other and hopefully you are not excessively burning oil. 

I am burning oil, what does that mean Mike? :confused:

[datzenmike]

Burning oil can be worn oil rings or valve seals.... or both.

[banzai510(hainz)]

your fine. 140 would be better but its a old Datsun!!!!!!!!!!

[Draker]

I agree with mike. Probably rings causing your issues. You can put a teaspoon of oil in each and retest. If the numbers increase significantly then.. that will confirm it.

[racerx]

Yes, it would make a difference if throttle is wide open. Try it, open throttle while clicking w a remote starter. Let us know what happened.

[sanyantho]

Thanks for your help guys. I will retest and report back.

[racerx]

Also the screw in type of compression checker is much accurate than the plug in type. Make sure engine is warmed up to operating temp. Feel upper hose of radiator if hot then good to go or check temp. Gauge.

[sanyantho]

Ok guys,

I retested and the compression is at 150-160 running temp with the thottle wide open. Does this mean that my block is good?

[racerx]

Thats better...ideal is like 170 since the book says so. But not knowing how many miles the engine has and what kind of work has been done u can only go with ur reading. Does it smoke like black or dark gray? If not keep on driving?

[Draker]

Yeah, I'd say it's good. The smoke is a little concerning but.. whatever. Just watch the level and it would be fine.

 

Does it smoke at idle, on acceleration, or on deceleration? Or all of the above?

[racerx]

When you accelerate, at freeway, for example, look at ur rear view mirror if its smoking like bluish color, then engine is going bad, maybe rings, if its like blackis or dark grey can be too rich. Also if the car hardly has any power going up hill then maybe time for a rebuilt but ur compression is good enough..like i said earlier keep on driving and start saving some money for a rebuilt.

[sanyantho]

I need to change the head the valve seat has stinking and the mouse trap spring is weak causing backfire when I accelerate on the #1 spark plug.

 

Hainz, I will be studying your video.

[datzenmike]

The mouse trap springs do not close the valves the only keep the rocker against the pivot pivot pin post.

 

How do you know the valves are stinking?

[racerx]

Maybe OP meant sticky valve. Speaking of valves, have u adjusted them?

[banzai510(hainz)]

How you know its sticky? 

 

I dont thing it will cause a back fire.

 

Condensor going bad. Go to eleltric ignition

Out of timming, dist going bad

Chain stretch,  ck cam timming

[datzenmike]

Too much clearance can cause the rocker to be thrown out. A dropped seat can also.

 

A stinking valve would present as a valve that is increasingly difficult to set the proper clearance. Eventually it cannot be adjusted as you have run out of thread and the pivot post has been turned down all the way. I posted a thread about a cure for a sunken valve. Not a fix really but a way to get more adjustment and keep it on the road. Presumably until a new head can be sourced.

[racerx]

If you can adjust your valves or valve and have clearance then it may not be sinking.  Adjust your valves now.  This is the first thing you should do and not assume that your valve or valves is sinking. You may be able to save yourself money and heartaches of a cylinder head job.  According to one of the Datsun books I have, a valve adjustment should happen every 10K miles.  Trust me on this..I just experienced it.  Do a search on Ratsun for sinking valve L18 engine.

[banzai510(hainz)]

when I valve sink past its limit you wont be able to put a feeler gauge under the cam lobe cause youll be out of thread post on the rocker post adjustment(to lower it down

[sanyantho]

Too much clearance can cause the rocker to be thrown out. A dropped seat can also.

 

A stinking valve would present as a valve that is increasingly difficult to set the proper clearance. Eventually it cannot be adjusted as you have run out of thread and the pivot post has been turned down all the way. I posted a thread about a cure for a sunken valve. Not a fix really but a way to get more adjustment and keep it on the road. Presumably until a new head can be sourced.

This is exactly what happened to my valve.

[sanyantho]

If you can adjust your valves or valve and have clearance then it may not be sinking.  Adjust your valves now.  This is the first thing you should do and not assume that your valve or valves is sinking. You may be able to save yourself money and heartaches of a cylinder head job.  According to one of the Datsun books I have, a valve adjustment should happen every 10K miles.  Trust me on this..I just experienced it.  Do a search on Ratsun for sinking valve L18 engine.

Yes, I adjusted my valves several times that how I know that one of them is sinking.

[sanyantho]

when I valve sink past its limit you wont be able to put a feeler gauge under the cam lobe cause youll be out of thread post on the rocker post adjustment(to lower it down

Exactly what happened to one of my valve. Thank you guys for your help.