The Stovebolt Site Forums The Shop Area Engine Shop please, please read its a great story/but long

i have been posting about this topic for over a year now. If you want you can read my many post concerning this issue.

In short though: I have had a problem with my engine that involved misfiring, terrible timing, timing bouncing when trying to time, the truck running like [censored] off and on,the seller telling me it was an old boat motor, whit smoke pouring out of the tail pipe, then a period of 3 weeks where the engine worked again, to a point wher i could not get it to start.


I finally did a compression test today. this is an inline 6 250 from a chevy c20. The compresion is as follows from the front of the motor to the firewal.... 130,130,120,120,110,90.

i then put some oil in the first spark plug hole and the compression went to 180.

My question is could these obvious bad rings cause all the symptonms listed above. I plan on doing a complete rebuild to cover any possible issues, but i am curious if this would cause all that.


thanks....... i think

First thing, what has been done and describe motor

Carb, igntion, plugs, plug wires changed, modified etc.

White smoke out of the exhaust indicates a blown head gasket, or a cracked block. Coolant is leaking into a combustin chamber.

Don't go for the worst just yet. Carefully diagnose all components. Points, condenser, firing order, fuel (make sure it is fresh, water in the gas will also signal a blown head gasket)

Take the easiest, and cheapest look ats first.

Keep us posted

i have done the following, new carb, new distubutor, new plugs, flushed gas tank, new fuel lines, redone the timing twice, checked the timing gears (they were in line), confirmed the harmonic balancer was true, confirmed the cam was in good shape, i am left with this compression test.

Sounds like the head has to come off. The white smoke indicates a blown head gasket or possibly a crack in the head, & # 6 is not firing. If it were the rings there would be blue smoke constant ly. Pull the head off, send it out & have it checked for cracks & give it a valve job. Did you notice if it was losing any coolant?

Agree with Jeffl. Check oil, if bad it will show. If not pull valve cover, it will look someone dumped a chocolate milkshake in it.

have already checked oil and everything thing else obvious, they check out fine.

A shot in the dark but here goes. I had a similar problem years ago with a 235. Rough idling, timing problems, etc but not the smoke.
I found a split in the steel vacuum line which runs between the distributor and the carb. Thought nothing of it but changed the line anyway and the problem was solved.
As I say a shot in the dark but who knows. Good luck.

when the truck ran good there was not a vaccum line on the truck, as the motor was running a boat. It ran great without the vaccum line. Since then i have installed a new distributor with a vaccum line which did not provide help the engine run better.

I really liked the "shot in the dark", in fact thought it was an excellent reply. I have a car with seemingly "miles of vacuum lines", under the hood, across the front, under the dash and yes even to the rear deck. Any guesses what it could be? No matter, point is when it is not running just right, I start troubleshooting the vacuum lines and components.

OK, now for a longer "shot in the dark", time for the flood lights kind of dark. I picked up on the phrase "old boat motor". I don't know if it is true, but I've heard boat motors have a different cam and they run backwards. That could put you out in the weeds if trying to time it as a car/truck motor. But if the motor was running backwards, wouldn't it have only one forward gear and several reverse gears? Perhaps, it has been converted to normal rotation, yet the reference points are misleading.

Hopefully, this will be more than a big laugh. Someone may pick up on my thought.

My thought...with respect. Comb the swap meets, Craigslist, want ads and junk yards, a running 250 has got to be less than your current investment and time on this project.

Good luck.

I had a bad coil once that caused some of the symptoms you have stated. I've read your past post, it makes me dizzy you've tried alot of advice from alot of people.
why not take it to a mechanic?
When my coil went bad a shop said new timing chain. It was back fireing running eratic. Power then no power, accelerate then not.

Goodluck

what would be the fun with a mechanic lol

And just another one of those beautiful shots in the dark..

Fuel?... Crap in the fuel tank?

And another possibilty is you stabbed the dizzy off by a gear tooth.

Hi, here's another shot in the dark to try, hot wire the ignition to bypass the ign. switch and all wiring between the switch and coil(battery POS to coil POS).NOTE:Remove hot wire BEFORE turning off the ign switch. Also make sure you have GOOD CLEAN grounds between battery, engine and frame.

When trying to time the distributor, do you have the vacuum line disconnected snd plugged? Does it run okay while the vaccum line is off the distributor only to start running bad when you hook the vacuum bsck up?

Could you have the vacuum line for the distributor hooked to the wrong port on the carb? That line should only have vacuum when throttle is opened. When vacuum falls to nothing the centrifagul advsance should be taking over.

If it is a former boat engine, the cam may be a little more radical and cause some headaches.

First thing to look for in a compression test is that all the cylinders are more or less equal. I think I saw where You say the motor was previously in a boat which means it was ran at wide open throttle with all the oil going to the back of the engine as the prow was out of the water. That condition would starve the front of the engine for oil and the parts in front will be worn more than the parts in the back of the engine. That also would explain the smoke, you have some rings worn out. Where there is smoke there is oil or coolant which will foul the plugs and make it run bad. It's time to take the engine apart and see what you have to work with. Everybody on here can give you guesses and opinions as I have just done but you will never know until you take the engine apart. You have been asking for a year and still don't hear an answer that you want to hear?

Fried Green, That is my plan. What the other posters dont seem to understand is i have done evrything known to man to fix this engine with out rebuilding it. I started tonight pulling the engine, i should have it out tommorow evening. I will updated this post or do a new one once i see the damage i have. The boat load on the rear of the engine would make since since the compression declines as i go twoards the back of the engine. I repeat to everyone in the forum...... I have done eveything on the surface to fix these problems, now its time for the real fun to begin.....an engine rebuild. As Agustus McCrae would say.... just once i would like to shoot at an educated man.

Thanks All

i have taken the engine completely apart. everything looks like its in good shape. Is there a way to visually inspect the rings and tell if they are bad.

No, once the rings are out of the cylinder, there's no way to tell if they were good or bad. You might slip a ring off a piston carefully, put it about 1/4" down a cylinder evenly by sliding a piston into the cylinder over it, and measure the gap between the ends of the ring. A service manual will tell you what the gap is supposed to be, and if it's noticeably wider, you can assume the ring is worn out.

BTW, how much oil did you put in the cylinder to make the compression go that high? Usually a tablespoon or two of oil is plenty to do a wet compression test. if you put several ounces in there, the compression can go way out of sight. The symptoms you're describing sound like you've got a worn-out camshaft, with a flat exhaust lobe or two. Be sure to check the cam and lifters carefully during the rebuild.
Jerry

2 tabelspoons, i just tried it in the first cylinder.

what should i look for on the cam

If you have it this far apart, break the glaze on the cylinders and rering it if it doesn't need to be rebored.

I have never added oil for a compression test. Oil will always make compression go higher. What is the point? I guess I've never used that method. Is it to see if all readings go up the same amount and remain consistant? Would it help indicate valve issues over ring failure?

To me, when the engine is at operating temperature with fuel/air in the combustion chamber is a true reading.

What I call a "wet" compression test is pumping the gas pedal once or twice before the compression test reading.

A leak down test would indicate if it is rings or a valve.

Just from what I've read, I would guess at a broken ring, worn distributor bushings, or a valve bent or not seating, or a cam lobe as HotRod L suggests.

Check the bottoms of the lifters where they ride on the cam. If you see anything other then a smooth surface, your cam or lifter is bad. The camshaft will have a trail around each lobe where the lifter has been running, they do not touch the whole cam lobe, just a portion of it, thats why i said to look for a trail. At the peak lift point the lifter will touch all the way across. If you have a dial caliper, measure the peak lift points, they all should be real close to each other, if you find a few or even one with less lift, get a new cam.


Don't forget to check the valve stem ends where the rocker arms touch. While there, check each rocker arm for wear at the valve end. Any damage at all, and you will need to change them.

Joe

no, you pour oil into the spark plug hole to test wif its a compression issue or valve issue. The theroy is, if the oil makes the compression change it has sealed the gap the ring has from being worn. You generally only do this when all the cylinders comprssion read off.

Another thing you might want to check is the rollpin in your distributor gear. I actually had this happen on a boat engine once. The idle was funny, and the timing would sometimes jump around, and sometimes wouldnt. Turned out that the rollpin had sheared on the distributor gear and was causing problems. Replaced it and it runs great.

-Nick

thanks, i am going to put a new HEI distributor on it after the rebuild.