The Stovebolt Site Forums The Shop Area Engine Shop Timing increments rusted out/ 250 engine

My timing increments have rusted out on my 65 chevy. It has a 250 motor in it and i am trying to adjust the timing on my new distributor. i got the timing degree number from a fellow bolter, but since the timing plate numbers are rusted and gone (so is part of the plate) i am going to weld a new plate but i need to know what the increments would have been. He told me i need to set it at 6 degrees BTDC. Any help would be great.

Set it where it sounds good, then go for a drive. Find a long up hill and lug the engine up the hill, if it pings, back off the timing just a bit.

These engines are really low compression and can a lot of timing. I run mine up around 11 or 12 degrees. You can also set it with a vacuum gauge, just adjust the timing till you get the highest reading of vacuum.

Joe

http://www.visn2.com/UsingVacumeGauge.html

Time it using a vacuum gauge

Nevermind i just saw your link




how do you use the vaccum gauge

thanks

Timing by vacuum....I was told here on the forum to set it at the highest number at idle 550 to 750 for our 235. Then reduce it by 2 pounds....why the reduction? Might have been for altitude we are 2,500ft. our vacuum is about 20-21 at it highest. I'm sure somebody will chime in with more information...T/C Steve

where do you buy a vacuum gauge

Any FLAPS Kragens, Napa, Auto Zone and not too expensive. Some people like my UNK only ever use a vacuum gauge to time their vehicles. I hope some guys that are really knowledgeable chime in with the proper sequence of things for your engine. On a 235/6 its just hook up to the manifold port( windshield wipers) adjust idle speed and turn the dizzy until you get the highest vacuum number then check idle again then check vacuum again for highest number continue until the highest number of vacuum at said idle speed. T/C Steve

you can find top dead center with a positive stop screwed in a spark hole. rotate it till it stops then back till it stops and mark half way between. i for one would not want to weld a new tab on the timing gear cover with it on the engine. an out of position weld with no room is good for a burn thru! the easy way might be to change the timing gear cover to one with a timing tab. you could use the positive stop method and a degree wheel to mark new marks. you can even mark your balancer and use any fixed point as position. but like everyone said vacumn gage will get you there.

i found top dead center and used the timing light but the mark on the balancer moves up and down iradicaly at idle. what would cause this. i have slwoy adjusted the distributor and it still sucks air then backfires. What else could it be. I have tried the plugs in all order and placement and it wont handle load. could it be the timing chain or a bad tooth on the gear

mswilkes65Chevy,

I don't know if your engine has a timing chain or gears...I'm guessing it has a chain. Anything that changes the relationship between ignition #1 and the mark on the pulley will show up as movement in the timing mark...did I say that correctly?

This could be a broken centrifugal advance mechanism, a bad vacuum advance unit OR a worn out timing chain. If you pull and plug any vacuum advance line and manipulate the throttle as you watch the timing marks, a loose chain will usually make the mark move erratically advance and retard...it will move around as the chain goes under tension and then goes slack.

If your engine still has gears, I'll take ten lashes with a wet noodle.

Stuart

the motor i a newer 250 so i am sure it is a chain. I have the vaccum advance plugged off when doing the timing. The mark on the harmonic balacer stay consistent when i hold the throtle at a constent rpm. Its just really eratic when its ideling. The vaccum advance is new. I have replaced the the distrubutor and carburetor during this troubleshooting. I have been trying to figue this problem out for about 2 months.

i guess my next move is to pull the timing cover off and inspect the gears and chain.

stuart get ready for your lashes, it's a he said it was a 250 right? has to have gears.

hoggy,

I just looked in a book for the 'new' 250 six cam gears. Yikes, take it easy with the big greasy noodle will ya!

Stuart

I am looking at the parts catalog, and the timing gear set with chain is only 54 dollars.

mswilks,

Slow down there buddy don't start ripping into the timing cover and pulling gears. A sure way to see if you have timing gear chain stretch is to take the distributor cap off and chalk mark the location of the rotor in relationship to the distributor. If you have a bolt in your front harmonic balancer the bottom pulley on the crankshaft, put a big socket and breaker bar on it, pull all the plugs so it will turn over easier and rotate the engine counter clockwise a 1/2 turn or so. Then get up and take a look at where the rotor is now in relationship to the mark. If its move a lot you don't have much chain stretch, if its move not at all or just a little you have a lot of chain stretch and need a new chain and gear set. You may have to do it a couple of times to get a feel for this procedure. I'd say if this is an old engine from the sounds of your rust story you are probably ready for a rebuild or at a minimum, new timing chain/gears and a oil pump. Hope this helps.

I will check that tonight. Here is an additional question. If the timing gear set is off - could it allow the enigne to run good at slow application of throttle. That is to say that if the truck is idleing and i push the throttle slowly, i can rev the RPM's as high as i want and it sound like its runnig perfect; but if i were to run the truck on the road it will chug and die ecspecially if i make it to third gear.

Your engine has timing gears, no chain. If you want to change them, plan on pulling the cam out, its the only way to change the gear. Its a press fit and the gear has to be heated and pressed, the crank gear just slides on. You may have some wear in the teeth, but its not going to be enough to cause your problem.

Get a second timing light and try it, some lights can't pick up the signal at low RPM and can cause what you are describing.

See if you can find a adjustable timing light, they have a dial on the back, and then set total timing instead of static timing. At 2000 to 2500 rpm you want about 32 to 34 degrees of timing. Just set the dial to 32 or 34 and run the rpm up till the timing mark quits advancing (2050 rpm), then turn the distributor till the line on the balancer lines up with zero on the pointer. You don't have to worry about where it is at idle, what really matters is where the timing is set at driving rpm. It takes a couple of hands to set it this way, but its much more accurate and takes all the slop out to the timing system.

Have you set the points dwell to 32 degrees? You have to set the dwell before setting to timing. You must check it!!!!!

There is around 24 degrees of mechanical advance in the ignition system, add in the 6 to 8 degrees of static timing and you get 30 to 32 total. On top of that you can add on vacuum advance.

At ideal driving conditions, you can have as much as 55 degrees of timing!

Joe

the only thing i can pretty much tell you is it's not a timing chain. have you tried changing the timing without the light just to see if it runs better? you might check plug wire order, i have been guilty of getting 2 switched once.

i took the timing cover off, and sory guys but it has a chain.

well whatever you do don't sell it because it's one of a kind. must be the only chain driven 250 chevrolet ever made. just to be sure we are all on the same page, you are talking about a 250 inline straight six right? there are 2 different sets of gears both will interchange but only as a set. but neither one has a chain, they are gear driven. is it a 350, a v8? i'm not saying you are wrong but you will have the only stock 250 chain driven cam i have ever seen. seems like i have seen some crazy racing applications for belt driven or something, but not stock. if it's a 350 i would just haul it off for scrap now.

its an inline 6 250 marine engine.

Does it have a Mercruiser ID tag on it anywhere? A chain-driven cam would turn the opposite direction than a gear drive, and that would require a totally different lobe shape and possibly a different firing order. Normal 250 Chevy gear drive cams turn counterclockwise when viewed from the front, while the crank turns clockwise.
Jerry

Could be why the distributor is acting funny, they are not suppose to spin back wards! What type of distributor did you install, truck or boat?

Lets see a picture of that timing setup.

wow, i didn't think about a marine engine. did you ever get it figured out, the problem that is?

Hoggy,

Does this mean I'm off the hook on the Linguine deal!

Stuart

I will have to see this chain set up to believe it, I been looking at boat sites to find one, all the inlines based on the 250 Chevy use the gear drive, not chain.

If this is a reverse rotation engine, then they might spin the cam backwards using a chain in order to use the same cam in both CW and CCW rotating engines. I still couldn't find a replacement timing set with a chain for a 250 .

Joe

stuart- i guess you'll have to be off the "hook" then. especially since it's a marine engine.

UPDATE: It has pressed on gears, but also has a chain that rotates on it. I pulled the cam out and had the gear removed with a hydraulic press then reinstalled everything with out the chain. Then I took the new distributor shaft and gear and put the old condenser and points on it. I left the vacuum advance off. I then set the timing and it was running great.... but it was blowing out black smoke. I figured it was running rich so I adjusted the choke baffle more open and the idle screw less. This got rid of the black smoke but the engine started to backfire again. So I left those settings alone and retimed the engine. It is, for now, running perfect again. Push the pedal real hard and it sets you back in the seat. WOW

Yikes....gears and a chain! Meshed gears create opposite rotation while chained components result in like rotation. This is still a very strange situation.

Stuart

This thread is worthless without pictures! We're witnessing a total rewrite of the laws of physics, and there's not going to be any record of the event!
Jerry

Amen HRL!


Stuart

aw come on guys, don't be so "cranky". maybe the chain was in a figure 8.