New (used) head smoking

[josh_t]

Hola ratsun. I bought an H72 head a couple weeks ago and everything went pretty smoothly changing it and getting it running again. But there happens to be one small problem, this new head smokes like crazy. This engine has NEVER smoked before. Not even once. It does it all the time but more so when i let off of the gas from higher RPM's. It is very random with the amount and frequency of it smoking though. Some times it decides it doesnt want to smoke at all though. It doesn't matter what temperature, although it smokes a little more when its fully warmed up. Anybody have any ideas?

 

EDIT: It is also most definitely burning oil, it's not too rich, and not steam coming from the exhaust. It's blue, has the unmistakeable smell of burnt oil, and doesn't dissipate in the air.

[DAT510]

Valve seals on topside of head?

[datzenmike]

Valve seals likely. Won't hurt to change them anyway.

 

Get a few feet of nylon rope and stuff down the spark plug hole. (tie a large knot on the outside end so it won't go in the hole) Turn motor with a ratchet on the front crank bolt and move towards TDC until rope is compressed up into the combustion chamber. This will hold the valves on that cylinder while you compress the spring and remove it to instal the new seal.

[josh_t]

well i didnt get the notification for these replies? Me and the seller were pretty sure of it being valve seals, but we wanted to make super sure since he offered to buy and ship new seals, and i didnt want his purchase to be in vain.

 

EDIT: anybody got any ideas on compressing the valve springs, like a common tool that can be used for this application. on the other head thats off the engine, i used a socket and tapped on the retainer until only it moved instead of moving the valve with it then i flipped the head over and pushed down on the head while it was on the socket and the keepers came out, but i dont have that option here.

[hang_510]

autozone should rent a spring compressor

[Skib]

anybody got any ideas on compressing the valve springs, like a common tool that can be used for this application.

 

$20-$30 at the parts store.

 

 

just buy one.

 

or some parts stores have rental programs for more specialty tools.

 

the massive pain in the ass it is to do without one is worth the $20 any day by a long shot.

[Zeusimo]

http://community.ratsun.net/topic/28804-how-to-replace-valve-stem-seals/

 

B)

[josh_t]

i've done half my seals so far. i didnt have time the first weekend and i was out of town, but i got the compressor pictured above. i'm gonna finish this thing tomorrow and we'll see how it goes. the old seals had almost no taper at all in them, whereas the new ones have a large amount of said taper.

[ggzilla]

It's more than the valve seals. The guides are worn out, and no amount of new seals will fix that on the A-series engine.

 

Use the rope method that Mike talked about -- that's how I do it. It lets you check the guides, which the air method won't. When you have the spring off, push the valve down a bit, then see if you can wiggle the valve stem side to side. If it has any noticeable play the guides are worn. If they are worn the umbrella type seals will help most.

 

The positive type fits tightly to the guide and the valve stem slides through it.

 

But with worn guides, shortly they will begin leaking, within a month or two sometimes -- because the valve is moving sideways relative to the guide.

 

 

Umbrella type moves up and down, and so will stay tight to the valve stem. The oil will run off and down the side of the guide

 

For OHC engines it can work differently because of how the oil flys around. But for the OHV you will still get some oil sucked in through the intake valve guides even with new seals.

[rbastedo]

I have a very similar problem, mine burns a bit of oil all the time but I really notice it most right after an oil change.

I don't know why this is, but that's what I have seen over and over.

It didn't burn any oil with the economy head on the motor but then I switched to (IIRC) an H89 head and wow the smoking started.

When the oil is 2 or 3 months old I really don't see it as much but yesterday I changed the oil & filter and then the first time out BIG cloud of blue smoke.

When this started I went ahead and replaced the seals, but it didn't help.

Just regular seals not umbrella type.

 

I suppose the ultimate fix is to have one of my spare heads rebuilt and then do the swap - wonder what that's going to cost me in the Seattle area?

Maybe I will get lucky with one of my other heads and it will be in good enough shape to just bolt on and work... :)

[josh_t]

yea i did notice a little tiny bit of play in them when i was changing the first half. i was kinda pissed about it. i sure ain't going to have machine work done to this head when i already spent a hundred on it. i cant afford this. L series swap keeps looking better and better. i'm gonna hate driving around a mosquito fogger for god only knows how long.

[ggzilla]

You can do the cheap fix -- have the guides knurled. Sometimes that works for a while.

 

But all you have to do if have new guides pressed in, then hand-lap the valves. Yes, it will cost about $100. Better to go to Pick-n-Pull and pay $50 for a good used head (check the valve guides before you buy!)

[rbastedo]

So all I really need to do if I understand correctly to find out if one of my other heads is ok is to compress the springs and see if there's wobble around play?

Sounds pretty easy.

BTW there is a way to replace the seals without a spring compressor, but it involves a hammer..

My son and I did it, he was 13 at the time, never too young to learn old tricks!

[ggzilla]

I do mine without a spring compressor when it is on the engine. I use a clean thin rubber hose, stick about three feet in the spark plug hole, then compress the valve with a fork thing. Two screwdrivers work too but it's kinda difficult because they tend to slip off. I've heard of the hammer trick but never did learn it.

 

When inspecting a used head, carry a water bottle. Place the head upside down and fill the combustion chamber with water. If it holds for 5 minutes, the valves are sealing good. Next, check for play on a valve stem. Use a small compressor (I paid $10 for one at a flea market) and see if the valve is tight side-to-side. If it's not, go on to the next head. If it is tight, check a few more (or all of them). Visually inspect for gauges in the head face and manifold faces. Clean-looking heads are best. Pass on slightly rusty heads.

 

Self-serve wrecking yards have a warranty if you want to do the checking at home.

[rbastedo]

Tell me more about what to do with the compressor, I have one here.

[ggzilla]

With the head off you can use a regular cylinder head spring compressor. Compress the valve spring, then remove the keepers. Remove the compressor. Push the valve off the seat about 5mm then see if you can wiggle the valve stem side-to-side.

 

Mine is a small unit, looks like this:

[ggzilla]

The service specification is (with the valve off the seat, move side to side parallel with rocker arm)

 

* At the valve stem end, 7.9 thousands (0.0079 inch)

* At the valve head. maximum deflection is 1.2 thousands (0.0012 inch).

[rbastedo]

Ah I see, thanks!

[ggzilla]

Josh, let's hope your seals are missing, so that adding them will be a cheap fix.

 

 

My engine acts exactly the same as Rick's description:

I really notice it most right after an oil change. I don't know why this is, but that's what I have seen over and over... yesterday I changed the oil & filter and then the first time out BIG cloud of blue smoke.

 

I think for two reasons:

1. When you change the oil, the new oil is poured right on top of the valves

2. New oil is thinner. I notice this when starting for a while after an oil change, then gradually less until the next change

 

My engine smoke is marginal. In time I know it will need to be fixed (I already changed the valve seals). Sometimes it's embarrasing when I start the car and smoke fills the air, but I don't see any when driving, or when rapping the engine in the driveway. By contrast my truck engine all of a sudden started smoking at idle, and when rapping the throttle. It had two slipped valve stem seals #1 and #4, and lower compression on the same cylinders. It had also crudded up those two cylinders and valves.

 

Datsun A-series engines seem to go about 150,000 miles before the valve guides start leaking a little oil, but 250,000 miles before the rings start going bad.

[RedBanner]

I sent josh the head, and filled the chambers before hand, they held all night not just 5 minutes.

How did the seals look when you removed them josh?

anything I can do to help let me know.

[josh_t]

the seals were shot. they were there but they were hard and had no taper to the inside of them whatsoever. i'm not even totally sure they were contacting the valves completely. there is play in the valve stems. i dont have a way to measure but i think its less than the service spec (hopefully). you can hear it moving but it doesnt look like much. is there any other symptom that i might notice like while its running that would indicate worn out guides?

[ggzilla]

Good. Just replace the valve seals. Use the umbrella type, because when the positive type gets hard, they won't be tight against the valve anymore (if the guides are worn).. What do you mean by taper?

 

 

The service spec for guide wear is exactly that -- not much. There should be almost no discernable movement.

 

is there any other symptom that i might notice like while its running that would indicate worn out guides?

Yep, a cloud of bluish smoke when you first start the car. That's the symptom. But it could also be caused by missing or bad valve seals. To distinguish between the two, inspection and measurement are required.

[josh_t]

you can hear it but you cant really see or feel it. i have smoke when i rev it and when it first starts but absolutely no blow by. the gases coming from my valve cover smell solely like oil. no exhaust or gas type smell. there is a bit of a taper that forms a little bit of a lip that touches the valve stem on the new seals and they are tight going on. (yes i used some kind of sleeve to keep the seal out of the grooves) and the old ones slide right off and almost have some wiggle room they are straight through like a rubber hose. i'm fixing to finish putting the other 4 seals on and i'll see what happens. i might have gotten the umbrella type except i already have the positive seals.

[ggzilla]

It might fix the problem.

[josh_t]

i'm hoping so. there are no other signs of it being any other problem besides seals other than possibly sloppy guides.