The Stovebolt Site Forums The Shop Area Engine Shop puffs of smoke when the clutch is let out.

Hey everybody,
Could anyone tell me why a 235 6 cyl. would puff smoke when you let of the clutch? It is a 4 on the floor and only does it when you go to third and fourth gear.

Thanks,
Slade

Worn valve guides

Guides or valve stem seals. Hopefully the latter.

What color smoke? Bluish would indicate oil, black would indicate rich fuel mixture.

It is a white/blue color .

Valve guide leakage typically shows up on decelleration or when accellerating immediately after decelleration. Shows up most markedly when going down a long hill in gear with foot off throttle and then accelerating. I wouldn't worry too much about it unless I was using more that a quart of oil per thousand miles.

So what would be best is if I replace the valve guides and seals?

BLUE52,

I assume your rig is a truck, not a car, and that the 4 on the floor is actually a SM-420 which would be compound low, 2,3,4.

So you start out in 2nd, shift to 3rd then to 4th. This means every time you shift it puffs smoke!

If the smoke is blueish, not black, as everyone above has stated, it's burning oil.

From the dynamics that generate the smoke, it appears it would be guides..as everyone has agreed. The rings could be contributing to it somewhat.

The engine is telling you it is old, burns some oil and it might be time for a rebuild.

No machine shop would do just the guides without doing a complete valve job..then, what the heck, why not surface the head...it's out anyway.

So, you have just "rebuilt" the head. According to the Guru's, the new head will doom the old bottom..As Baldy said, drive it and enjoy it.

When you are using a quart of oil every 100 miles, and the cops are giving you tickets for smoking exhaust, think about a rebuilt engine.

If you dig working on these old rigs, drive yours the way it is, and start right now, finding another engine to rebuild at your leisure, and as your budget will allow.

Stuart

Many tune up things to consider here but let's look at compression and engine mileage first.
Compression testing the cylinders:
It's really not necessary to know exactly what you should have but 125+ is a good figure to start out w/.
Pull all spark plugs so engine turns freely. Test all cylinders and write down figures. They should vary little unless you have a duff cylinder. Now go back to each cylinder and do a 'wet' test. Spray wd40 or equivalant in that cylinder you are testing only. Connect compression gauge again and write down what you now have. I believe these should be about 125-145 psi. readings for a good engine.
IF:
> the first readings are better than the second ones your rings are bad. By putting that spray of lub. into each cylinder it helps to seal the rings a little better than they are. :o

> The second readings are better then it's your guides and seals are bad.

Your favorite mode of transportation has lost some of its "zip"? You think its time for a tune up and maybe you have had your engine tuned up but it still doesn't have the performance it used to have. Maybe its just a little "slow & nervous" when idling. There are several things that can be the cause: bad spark plugs, bad plug wires, worn distributor, leaking valves, or worn or broken piston rings and the list goes on. Its time for a compression test to determine if you have bad piston rings or leaky valves. The pounds per square inch of compression varies with each engine. If you want to know the compression specs for your vehicle, consult your shop manual. To run a compression test, you need a few basic tools. First and foremost is a compression tester. With your tester, check each cylinder and record the results. There should not be over 20% variance between the highest and lowest reading. If there is a greater variance, you may have internal engine problems. To further isolate the problem, run a "wet compression check". This is done by squirting a some oil in each cylinder (I use about a teaspoon per cylinder). If the compression comes up to specs with the wet check, you have worn or damaged rings and are looking at engine rebuild. :rolleyes: :mad: If the compression doesn't change, you have valve problems and usually can solve your issues with a valve job. :rolleyes: However, bad valves and worn or damaged rings can be partners. So, when you pull the cylinder heads, check for ring grooves, cylinder cross honing marks and other signs of cylinder/piston damage/wear. You should also consider the mileage on the engine. If it has high mileage, many times a valve job will cause the engine to start using oil. If there is evidence of wear in the cylinders you might want to re-ring the engine as well. The compression test may not help you pinpoint exactly what the problem is, but it will help you narrow down the possibilities. And for that alone, it's worth doing!

I think I got this right, autoshop 101