The Stovebolt Site Forums The Shop Area Engine Shop how 'smooth' is your 235 I6?

I was messing around with my truck (56 3100) and revved it up a bit to simulate rpms at various road speeds. I throttled up to 1000 rpms, 1500, 2000, etc., up to about 3000. Its not all that smooth..

Nothing violet, no excessive shaking, etc., just a little rough and some vibration was felt through the body. The engine runs very well and is in excellent tune - in fact at idle it was turning at a bit under 400 rpms.

is this typical and are there any improvement ideas? Maybe its just the nature of the beast.

It's all relative to the person in the seat, my '56 235 would be rough to my wife's Nissan grocery getter.

Have you checked the compression lately? A few pounds of difference between cylinders can cause a little roughness, without creating an actual miss. One slightly tight valve clearance can make a difference in smoothness, as well.
Jerry

The 235 in my '57 used to run very smooth with just a slight ticking sound. I had it at a local garage for something else so I asked the guy to set the valve clearances. He said he also adjusted the timing a little. The ticking is now gone but it does not idle as smoothly as before. I guess I'll have to find time to check the valves and timing.

Good idea to check the compression. I haven't looked at that lately. I adjusted my valves just last week and it is quite possible I have a tight clearance or two. thanks for the tip.

to follow up on jfnar's post - the engine idles very smooth - I can get the idle into the low 300 rpms if it want. The roughness comes with revs, it feels like a slight imbalance problem actually.

If you have a delay-flash timing light, check the centrifugal (not vacuum) advance. It should increase smoothly as the RPM goes up. The advance weights and springs are under the breaker plate, so it takes a pretty good teardown of the distributor to service them. Since that system is out of sight, it can get neglected. A common problem is rust on the weight pivots and/or hardened grease which causes sticky or no movements of the weights. Occasionally you'll find a weak or broken spring that allows too much advance too soon, resulting in rough running.
Jerry

thanks Jerry. I do have a delay-flash timing light, and set the timing using the vacuum gauge method so I have never checked the mechanical advance.

I like the slogan that Sun used to put on all their test equipment- - - - -"We test, not guess!" I always assume something is wrong, broken, or maladjusted, until I prove it's right. When I was running diagnostics for a big independent shop about 25 years ago, they kept cars lined up about 3 deep behind my service bay, including a bunch of cars the other shops in town had given up on!
Jerry

Just wondering on the checking of the centrifugal advance . how would you see that once the bb has moved out of site and would disconecting the vac first be a good idea. I ask because my 235 seems to run out of power about 3k and this may be a idea. also thinking of dwell. Sorry if this hijacks the post.

Remember I asked about a "delay flash timing light"? At any set engine speed, the control on the light is turned, and the timing marks are brought back into alignment by delaying the flash of the strobe. Then a scale or a digital readout indicates how much advance the spark has for that speed. My Snap-On timing light has a built-in tach, and a timing indication so I can toggle back and forth. I usually check the advance in 500 RPM increments from idle to cruise speed, and compare my readings to the factory specifications for the engine I'm checking.

Vacuum advance only works at light throttle cruise, so by disabling the vacuum during the advance check, only the operation of the centrifugal weights is being checked by increasing speed. It's impossible to put enough load on an engine in the shop to drop the manifold vacuum so the vacuum advance drops out, unless the shop is equipped with a chassis dyno. I've got a dyno that bolts onto a bellhousing and puts load onto the engine with water, but I haven't gotten around to building a set of rollers and a load cell to check the whole vehicle.
Jerry

Those delayed flash timing lights are really useful. i converted an old camaro to a GM TBI fuel injection system and that tool was instrumental to figuring out the spark advance (Electronic Spark Control) that the ECM was commanding.

Yes it worked well . looks like I have 30 deg in vac and then the cent kicked in. I had a dwell meter on at same time and it was 42 up to around 2k then dropped to 30. And the engine was smooth from 600 to around 3k To help with the orig question.

Your numbers don't make good nonsense! The total vacuum advance should not be more than about 10-12 degrees, and MUST BE DISABLED before attempting to measure a centrifugal advance curve. Centrifugal advance should begin somewhere around 1,000-1,200 RPM, and should be complete somewhere around 2,500 RPM with 25 degrees or so of advance over the initial setting. Depending on which flywheel you have, the BB will be somewhere in the range of 0 to 5 degrees before top dead center. If the initial plus centrifugal advance totals more than 35-36 degrees at cruise RPM, you're trying to run the engine backwards. Vacuum advance can add up to 10-12 degrees, but only at light throttle cruise conditions.

A variation of 12 degrees of dwell means you've got worn out bushings in your distributor, or your dwell meter is lying to you.
Jerry

I had a freshly rebuilt 235 which you couldn't tell was running at idle, but vibrated noticeably while driving. I was ready to ring the neck of my machinist for "balancing" my crankshaft, when for giggles, I checked my brand new motor mounts and apparently the "mechanic" who installed it forgot to tighten the bolts on the rear mounts! This "mechanic" is an opinionated, know-it-all, self-loathing, drug addicted (tobacco products), old, bald, but not as fat as he used to be, idiot sometimes. He talks to himself unintelligibly and spends to much time on truck forum sites...
Carl

The numbers could be wrong. What I did ,with vac connected I put the light on the Bb, Then raised up the idle and watched as the Bb left I adj the timing light to 30 . The bb stayed steady till about 1800 then moves again. I assumed that this was the cent kicking in. Probably a mickeymouse way to check but as a front yard mech its all I have.

ref dwell drop. could be bushings. This meter hasent lied to me since 1968.Easy way to check bushings?

Grab the rotor and see if you can move it from side to side (NOT rotation). There should be little or no movement. If it moves enough to see a visible change in the point gap, the bushings are shot. The breaker cam and the shaft that the rotor mounts on is mounted to the upper part of the advance assembly, and rides on its own bushing surrounding the lower shaft that connects to the drive gear. The lower shaft runs in bushings in the distributor body. All the above bushings virtually never get inspected and rarely if ever lubricated, and some of these distributors are 70-something years old.
Jerry

Carl, I think I may know that guy.

Carl, I shave a guy like that every few days, and I ain't a barber! He's an ugly one, looking back out of the mirror at me!
Jerry

Smooth operation is (and always was) one of the advantages of the L6 engine.

Carl, that joker was around my shop just the other day. I had to go behind him too

re. smoothness. My 216 is pretty smooth, so smooth if it wasn't clacking the valves I wouldn't know it was running. well, that and the drops of oil underneath it

re. distributer, turn it so the points are just about to open but are still closed.
Disconnect the coil lead to the points, connect up either a continuity checker or OHM meter - black lead to ground - red lead to where the coil lead connected to the points, wiggle the rotor button, not around but side to side as Jerry indicated. If you see the meter change state or the light go on/off you've got worn bushings.

Does the dist wobble around when the engine is running?

Interesting. I put a meter on the points and put some pressure on the shaft and it will open the points.Probably 10 thousandth . does this mean bushings? and where would I find them ? or rebuilt dist? If I can find them is this a tap out tap in project or a special tool project. Will start searchin for bushings and the manual. Thanks

And when running the dist has a slight shake. A piece of wood between the motor and dist will stop it. When stopped it moves also . Wore out housing or block?

There used to be rebuilt distributors available. Now, I'm not so sure. Some Oilite bronze, a lathe, and a couple of precision reamers would be needed to custom make a set of bushings. It's a fairly straightforward procedure for anyone with some basic machining skills, but I doubt that the bushings would be available off the shelf at the average neighborhood parts store. I've got a junk distributor or two stashed away, so I'll make a few measurements and try to post some dimensions for anyone interested in doing some fabricating.

The housing is a slip fit in the block, and the entire housing rotates with the vacuum advance. A little slop in the block isn't uncommon, and it doesn't have a great deal of influence on how the engine runs. Some people like to run a ground wire from the dizzy to the block, but if you do, use a piece of high-flex wire like a piece of a voltmeter test lead. Regular primary wire will fatigue and break due to the constant movement.
Jerry

Rockauto.com sells three brands/makes of 1956 235 distributors from $75 to $120 plus core.

NAPA used to have the best price, but they now sell one for around $200 plus core.

I saw LMC has a new one in their cat. but does not say what all comes with it. points, cond , base plate. Will look at rockauto. I do not have a lathe or access to one so the new/rebuilt may be the way to go. Just hope new is not a offshore product.

looked at rock they dont show a 59 but do have a 56. is that the same? write up on part looks good and every thing comes. Anyone ever use one of these?

Rockauto list one for 1959 235 (3100 - it would work on 3100-3800, at least): $115 plus core

Recently I rebuilt a distributor for a Triumph TR-6, which uses a Delco distributor almost identical to a stovebolt. I bored and reamed the housing and fabricated upper and lower bushings from oilite bronze, then used a chucking reamer to line-ream the bushings so the shaft would run true. If you can get a rebuilt dizzy for under $200.00, you'll probably save money over having a machinist tool up and rehab your current distributor. There's a lot of setup time involved, and at least one precision reamer, maybe two involved in the job.
Jerry

59chevy36,
I am curious whether you have the grease cup with the spring and the disc on this distributor. The reason I ask is that I am curious as to whether the absence of, or the lack of the recommended maintenance of it will lead to accelerated failure of the bushings. I also wonder if the cup/spring compensates for normal, eventual wear of the bushings.

If the grease cup, spring, and Bakelite washer are in place, and not gunked up, the pressure of the Bakelite disc against the rotating shaft will keep the shaft loaded against one wall of the bushing. That should minimize the tendency for the shaft and the breaker cam to wobble. Unfortunately, the grease in the cup has a habit of getting harder than woodpecker lips!
Jerry

Thanks for the link. I had looked under 36 and only found the points. Looks like it will be Christmas inJuly. mine has the cup and a few years back when I replaced the oil pump I cleaned and relubed it. I will blame the premature wear on old age. Thanks again for the info. will update after the install.