The Stovebolt Site Forums The Parking Lot '60-'66 Trucks Ignition problems- 305E V6

New compression gauge, new numbers. Throttle and choke open.
1 = 20
3 = 70
5 = 80
2 = 82
4 = 70 once, second time 0
6 = 0

Is this 100% timing chain/gear broken???????? or what else to check???????????

As I mentioned long ago, I vote timing chain. Driving one minute shut it off won’t start. Classic timing chain. We’ll see. Thanks for the update.

Wow that took awhile. Definitely sounds like its out. I think i saw a timing chain on here somewhere for sale.

With 60,000 original miles on a bullet proof motor with known reliability, it was not on my mind. Can't believe it really. I will have him take off valve covers and take a look. Just is case all heck broke loose up there. That's a long shot but has to be checked before teardown. If he does not have a double chain I will have him convert. Any other ideas before teardown????

One family truck, all they did was use it for camping.

Could it be as "simple" as stuck valves? E10 loosened years of crud and the valves stuck in their guides? I don't know the GMC V-6s enough to know if there is a valve-piston interference problem, but I'd be thinking stuck valves before a broken timing chain.

An anecdote - I tore down a "runs good" 454 years ago that had shed the nylon portions of the timing sprocket. Even with that, the chain was very loose, but still caught on the remainder of the aluminum sprocket, and hadn't jumped time. Of course the nylon nibs that migrated into the crankshaft oil passages (filter must have clogged and bypassed) didn't do bearing lube any favors. The crank was salvageable, but had to be ground (fortunately it was standard dimension). I know the GMC isn't a big block Chevy, but I'm thinking the GMC is pretty robust.

Tear the engine down, and see what's going on. My two cents

Doug

Don't think all the valves would be stuck.

Bart/Amos - I was only throwing out a suggestion, since I hadn't seen it mentioned in this thread. IMO, it would only take 3 of 12 really stuck to give those readings like that on a cold, dry, possibly tired engine. Or are those numbers for a "wet" test?

But my main point was, it's time consider a systematic disassembly and inspection, and the top end is easiest to get to, so why not start with making sure the valves are free (and move with engine rotation, as I think was mentioned earlier)? If possible, a leakdown test might be a better starting point, but it's likely to show all cylinders leaking at the valves from what you describe and have been working with the OP, so the V/Cs need to come off, anyway.

Again, just my two cents. Cheers!

Doug

It's Bartamos not Bart/Amos

Didn't know readings like that can only be a few valves. Not very knowledgeable on that. Some of the things mentioned may not be feasible for some owners to do. I have asked him two days ago to take off valve covers and when his business schedule permits, he will. I can't assess or train what to look for over the internet. Tearing down in his driveway scares me. I believe I'm just going to say a general statement that it seems like timing chain or other associated parts. Not recommend a DIY or go to a shop or get a Chevy motor. I will answer any questions after that and stop trying to find and fix. I will recommend returning to Stovebolt with a new post and explaining the problem and history of tests. I am not qualified to help with a teardown over the internet. If I was doing it I would take off bumper, grill, radiator, radiator crossmember and etc. to sit in a chair and pull all the stuff off the front of this Big Block 305 V6 monster. But not out front in my driveway, which is where it is stuck. I've had several of these motors. Solid lifters.
If the rockers are in tact, springs in tact, everything going up and down OK with motor cranking, then unfortunately it's Kings X for Jimmy. Painful as it is, a decision will be made on how to continue..........

Can someone tell me if a blown head gasket can give these numbers??????????

Would it do any good to squirt a little oil down each cylinder in case ALL the rings are stuck or not sealing? Again it seems like all cylinders can only exhibit low numbers due to chain or gear failure. The thing that puzzles me is we check timing regarding no. 1 compression stroke and rotor position. We rotated around twice to see if rotor returned, it did. Although I was not there, it seemed he did it correctly. Yet it won't fire once. Has spark, has gas, seems timed but no compression. Does that point to head gasket??????????? Can all cylinders be "washed"???????

Just going to toss this out there. In my neck of the woods there are lots of “Mobil Mechanics”, some even ASE certified, who will come to your home and check the engine out. I don’t know what the OPs financial position is, but it might be worth a few bucks to get some professional help. I would be wary of one that doesn’t have grey hair. An hour or so of the mechanics time is going to accomplish one of two things. #1, hopefully the engine will be setting there purring like only a 305 V6 can do, or the OP will know to start saving up for a complete overhaul. Just a different way to proceed.

Not a bad idea at all. Gets me off the hook too

Old engine with solid lifters being driven shortly after getting it started without running it back in without revving it and checking for proper lubrication after years of sitting is never a good idea. If you are lucky, you will be able to get away with just new pushrods (to replace the bent ones), lifters, maybe a few rocker arms, maybe a cam, possibly a replaced valve or two and a timing chain. the lifters in the block could be stuck, the valves in the head could be stuck and bent. Unlike hydraulic lifters, solid lifters are unfogiving. Any of those components jamming will cause and old timing chain to jump time.

I look at it for free if it was local. Got all the qualifications!

FYI: I worked for Chevrolet as a dealership flat rate mechanic for 25 years rebuilding engines, and I am 66 years old and don't have grey hair.

Not sure if it will apply to this particular motor, but if you're trying to get a look inside without tearing things down to far I have had success renting a flexible inspection scope. Some have a light built in and some don't, if you don't have a light on the end of it it makes things harder (trying to juggle and aim a really bright flashlight down the spark plug hole is no fun). I would think that if it were a head gasket there would be some oil dribble from the head or heads, unless the motor was super dry on the top end (or already covered in oil to the point where you can't tell if it is leaking). using a flexible inspection scope and very slowly turning the motor by hand (if it still spins) should help to get an idea of what's going on. It helped me find a broken rod on a dormant Benz motor years ago, was better to find it that way than to try to start up without knowing.

Doing better than me, been with G.M dealers since 1980, I'm 61.5 & have lot of grey hair, happy to have hair!

Here is the problem in my little mind. Don't want to recommend tear down of timing chain. Don't want to recommend taking heads off. Don't want to go after the wrong thing.
Keeping in mind that ALL cylinders are low:

1. If it was head gasket, it's a V6, it has two head gaskets. Both blown?
2. If it's timing chain/gear, why did rotor return to point right at no. 1 after rotating motor 360 several times? That seems to indicate no slippage and at least no. 1 would have compression.
3. I don't know if this motor is an interference motor or not. If not, there are no bent valves.
4. I guess if all pistons/rings were stuck or cylinders washed dry, that would be no compression and I guess not even one cylinder would fire?
5. It does have spark, it does have gas, if the test were done correctly by poster.
6. A leak down would be good to do.
7. He does have a scope. All you could see is piston top and walls. I hope they are going up and down. A straw in each hole will tell you that.
8. The 1, 3, 5 bank is not a whole lot different than the 2, 4, 6 bank.

Going to add two good squirts of oil into each cylinder and see what that does for compression. Trying to be sure with limited tools and limited experience and over the internet, before recommending DIY tear down or mechanic services. If a miracle happens and cylinders come up to 125, that will be nice. If not my guess has to be the Martin opinion......timing chain. Should not be that with 60,000 miles. Double roller chain very strong, No stretch in 60K miles. Big strong forged steel gears, But............ the bad thing is I know I'm wrong somewhere.
Going to also repeat the rotor test again now that motor has been cranked a lot. Bring no.1 up to TDC on compression, look at pointer, look at rotor pointing at No. 1 . Then rotate motor 360 and look at pointer and rotor again.

Pull da cap. Look at da rotor. Turn crank in 1 direction till rotor turns. Then turn in da crank in other direction and sèe how far, or degrees it takes to turn rotor. That will at least tell ya if da timing chain is a sloppy mess. Stretched, gear stripped, or other timing issue? Im not convinced that #1 compression stroke is being verified and-or rotor is pointing at #1 when it supposed to. Theres no way this truck went from good running to inoperable in a flash w/o a mechanical failure if all other necessary components are in place.... Fuel, Spark, ..... the other 2 are Timing and Compression that seem to be questionable?? Unless of course da cylinders are washed down?? Then oil squirting will verify that. Unfortunately like previously stated, maybe da kid needs a better hands on, knowledgeable helper? JMO

He's not a kid. He's 49. Got confirmation pictures of the pointer and rotor.

So I have reread through the entire 14 pages of this thread and am impressed at the effort made by Bartamos in particular and others in trying to solve Jimmys issue. One thing that I missed on the first read was the latest compression test results. Cylinder #6 had a reading of 70 and then 0 during a subsequent test. I don't recall any mention about oil pressure PSI or the removal of the valve covers to see if the top end (much less the rest of the engine)is being properly lubricated. A reading of 70 PSI and then 0 would indicate to me that a component is sticking for a low reading of 70, or a reading of 0 indicating (to me at least) either a stuck lifter in the block bore or inadequate lubrication of the rocker shaft (which would affect the travel of all the rocker arms), or both, resulting in at least some if not all,valves not closing or opening effectively causing low compression readings. I would also suspect possible cam lobe damage as well. To state the obvious, head gaskets and timing chains are not going to momentarily repair themselves and then fail. Also, metal components, as we all know, expand when they heat up and contract when they cool.

I am more convinced than ever, based on what I have read, that the issue is lubricant related. If it were my engine, I would first remove the valve covers and assess how much fresh oil is visible on the rocker arm shaft, rocker arms and head in general ( it will also provide a good general assessment of the lubrication of the engine parts not visible). If lubrication is fresh and obviously sufficient, I would then assess the condition of the pushrods (at piston TDC you should be able to spin them with your fingers); if they look to be unbent I would proceed to turn the engine over BY HAND (wrench on crankshaft) and assess the rocker arm and valve travel. If all rockers and valves seem to be moving freely, I would then adjust all the valves, one cylinder at a time, and then do another compression test. Compression test readings are always going to be low if the engine has not been warmed up; as in this situation that is not possible, look for consistently close readings between cylinders (10 to 20 PSI would be optimal). Using a oil can to spray oil into the cylinder top and wall gap with oil before testing will temporarily help seal the ring / bore gap and raise the PSI reading. Two adjacent cylinders having a low reading in contrast to normal readings in the other cylinders often indicates a 1 blown head gasket, 2 a cracked cylinder wall between the cylinders, and 3 a cracked head; all three are most often a result of overheating the engine.

Having done all that and everything looks good, I would imagine it would come back around to timing and ignition settings. Below I have provided some valve and ignition info that hopefully will help get it going, from the Service trade Edition of Motor Truck and Diesel Repair Manual 28th Edition:

1966 GM 305-E V-6 engine:
Spark Plug 45ns Plug GAP .035
Distributor Point Gap .019 Timing Mark 5 degrees Firing Order 1-6-5-4-3-2
Valve Lash Intake .012 HOT Exhaust .018 HOT ( Cold, I would look for intake .015 to .017 and exhaust .021 to .024 and plan on readjusting them once the engine is running and hot ). Valve spring pressure (LBS @ inch length) 200 @1 1/2
Compression Pressure at cranking Speed 135 PSI

Valve Adjustment Procedure (verbatim from manual): With engine at operating temperature and rocker arm covers removed, turn adjusting nut on each rocker arm until proper clearance is obtained between valve stem and rocker arm.
Best of luck

with 4&6 reading so low I would hope for a head gasket or a cracked head on that side, maybe even some head warping from excessive heat. I had seen it happen a bit out here where it gets so hot. occasionally improper torquing of the head bolts could lead to something like that, though this looks worse that any case of that happening that I've seen before. another wet compression test with fairly consistent results may help pin it down.

Good info guys.
I don't believe the cranking of motor with a slightly slow speed starter or weak battery would produce enough oil pressure to reach rocker area. We will be inspecting that. Next test is oiled cylinders.

Will take off covers and spin push rods by hand, check rockers, springs, and watch overall operation and oil flow during crank speed.

The hand crank pointer/rotor test will be repeated. We will reverse direction, as suggested, to observe slop.

It would be nice if we detect faster speed crank after oiling cylinders by hand. It would be nice to see at least 4 cylinders go to 100+ psi.

Next opportunity for OP is Mon-Tues

I have just asked him if he ever changed oil. If he has a cartridge oil filter or spin on. If he changed cartridge.

EDIT: Oil not change for a long long time. Filter not changed. Unknown if that's 33 years or not. A sitting motor will form condensation during weather cycles and have dripping water inside valve covers and crankcase. This can turn into a living environment for "swamp thing". May not pump thru unchanged filter and into motor....or may pump some sort of unknown chemically altered fluid into motor and "stick" it up and dry it up. In addition, may have allowed washing during the test drives. A series of eventual loss of compression.
I want to hand flush all of the valve train and let it drain into pan, then drain pan. Change filter, add 5 qts thin oil by pouring over valve train and do the oil squirt compression test. What should top of motor be hand flushed with? Gas, Mystery oil, kerosene...... keeping in mind is will be drained out. Don't want it to circulate anyway.
Don't want to add more bad 33 year old oil to the situation. Just trying to give the oil-in-cylinder compression test the best chance, as this may be the last chance, before teardown.
My fantasy is we get enough compression to start, oil circulates and fees up motor, then change oil a few times and "whalla", it's fixed. aye? No damage. I am hanging on to that it has spark, is timed and getting gas.

One of us is gummed up and washed out........me or the motor.

Based on what you have described, a teardown, thorough cleaning and evaluation of the internal components is the only truly reliable solution. The possibly 33 year old oil has, in all likelihood, solidified enough sludge in the bottom of the oil pan to at least partially clog the oil pump pickup screen and possibly the oil pump itself. The oil that is still liquid has been mixed with condensed water and has been circulated (however weakly) through the engine so the crank, rod and cam bearings will need replacing. The cylinder walls, at the very least, will need to be honed, and may need to be bored out. The piston rings will need replacing if honed and the pistons and rings if the cylinders are bored out. The rods and wrist pins should be evaluated. The lifters will need replacing and their block bores honed, and replacing the cam would be a good idea. New oil pump. All engine block oil passages, after removing the threaded pugs at their ends, need to be cleaned out with a gun cleaning rod with a copper or brass brush (my personal choice is .22 caliber). All freeze plugs should be replaced.The crank will have to be evaluated, including measurement, to see if it is reusable. The oil return passages in the heads will have to be cleared. By rights the stripped block should be hot tanked at a local machine shop and checked for any cracks that may not be visible to the naked eye. No mention has been made about the cooling system, but if the oil is that old, chances are the 33 year old coolant lost its effectiveness long ago and may have frozen in the block at some point, cracking it. Those cracks will widen as the engine warms and mix more contamination into the oil from coolant passages as well as possibly causing low compression and / or hydro-locking of the cylinders after the engine is shut off.

The cleaning process with such old oil and solidified sludge is not just a matter of clearing passages, but also insuring that there isn't any sludge left in recesses that are not easily visible. The new oil in a newly rebuilt engine (or any engine for that matter) can soften old sludge to the point that it will break away from the surface it was adhered to and travel through the engine, contaminating the new oil on the way and possibly causing new blockages depending on where it gets caught in the engine.

I really don't want to be the bearer of bad news, but in my opinion, any attempt of a less thorough repair at this point is a roll of the dice. Even if it were to run, however poorly, it won't be reliable and at some point, not so very far in the future, will fail, and in all likelihood will not be repairable.

The motor is absolutely not worth it. Tearing down for the experience, or to try and identify the issue, would be entertaining. A good running 305 V6 can be had for $200-$500. They are a 100% boat anchor for "performance" and max out at about 3400 rpm. Good torque, well built. If I had this situation and I would buy another or drop in a SBC or BBC. The motor is just rare enough, and has a following, to where the parts are worth money. Pistons, rings, some of the valve train, gears, timing chain, and other parts are either expensive or a bit hard to find for a rebuild. The nostalgia factor of being his Dad's truck, bought new, may have an effect. This is why I'm trying so hard, and seem so silly, to find a way to get it going without teardown. I do realize everyone is probably right and a teardown is already past due. I will report back in a week or two. I am familiar with these motors and they are an engineering marvel. They have a very very strong oiling and water circulation design. Very strong metallurgy. Could withstand the lack of oil and washing.

Motor designed for 200,000 miles back in 1959 after GMC told to cease and desist in selling trucks with Pontiac V8's with a GMC sticker on valve covers.

First GMC V6:
HIGH OUTPUT OIL PUMP:
capable of pumping 14 gallons of oil per minute, provides extra circulation at all engine speeds
. . . extra protection and well oiled surfaces on all vital moving parts. Engine is lubricated as
soon as it's started. Cam lobes dip into a built-in reservoir of oil as the camshaft rotates,
preventing cam and valve scuffing - a major reason why this engine gives long, dependable service.

135 GALLONS OF WATER:
(at 3400 r.p.m.) Are pumped through this engine every minute. With thermostat open, only half the
water goes to the radiator, the other half returns to the pump through a by-pass. This results in
excellent cooling ability. There is less than four degrees variation in water temperature throughout
the engine. This checks the possibility of hot spots. Here's cooling efficiency that is not matched
by any other comparable size engine. Life of pistons, valves, valve guides and spark plugs in much
greater, and the possibility of head-cracking is held safely in check . . . further proof of the
durability and long life that is built into this engine.

FULLY-MATCHED COMBUSTION CHAMBERS Smooth, precision-machined combustion
chamber minimizes carbon deposits, hot spots & pre-ignition. & there is uniform combustion in all 6
cylinders for smoothest engine operation. 6 equally-spaced head bolts surround each cylinder to reduce
bore distortion, & guarantee gasket sealing for long engine service.

RELIABLE TIMING LINKAGE V-6 roller timing chains are double-strand, for
double durability.

FREE-BREATHING INTAKE VALVES Forged from steels with high resistance to warping,
pitting, & wear, extra-large intake valves let the V-6 breath freely, for higher volumetric efficiency.

FREE-VENTING EXHAUST VALVES Compared with other engines of equal displacement,
V-6's have the largest exhaust valves of all -- to keep back pressure low, efficiency high.

HARD FACES & INSERTS Tough, Silchrome XB-steel exhaust valves, hard-faced
with Ni-Chrome

Spark plugs are on the inside at top of motor away from exhaust manifolds. Long reach plugs provide greater heat sinking. Plug wires stay on top of motor.

"SCUFFPROOFING"DIP Before pressure lubrication takes over on engine starts,
V-6 cam lobes dip into a special oil reservoir. No "dry scuffing" mare cam or valve-lifter faces!

POSITIVE VALVE ROTATION A positive ratchet action rotates every valve on each cycle.
Contact surfaces stay clean for positive seating. Standard, 305C & up

M400 CONNECTING ROD BEARINGS Big, long-life M400 bearings are used in V-6
connecting rods. Low-friction tin & aluminum alloys are backed with a layer of steel for extra strength.

EXTRA-LARGE MAIN BEARINGS Huge, M400 main bearings provide solid support for
the crankshaft, & resist wear by spreading the load over extra square inches of bearing area.

PRECISION-FITTED PISTONS In every V-6 the big, deep-skirt aluminum pistons are
weight-matched, & precision-fitted to the bores, a cast-in steel band controls heat expansion.

SHORT, RIGID CAMSHAFT Extra-wide camshaft lobes are flame hardened & phosphate
coated to resist wear. Four big bearings carry the shaft for precise valve operation.


RUGGED CONNECTING RODS Piston power flows smoothly to the crankshaft through
big, forged-steel, I-beam connecting rods -- all balanced to within the weight of a cigarette!

SHORT, STIFF CRANKSHAFT This husky crankshaft helps conserve engine power &
extends bearing life, because it has the strength & balance to minimize deflection & vibration.

RIGID, RUGGED BLOCK This block has strength to spare for resisting internal strain --
strength from it's super-tough iron alloy, staggered cylinders & short, deep-skirt design.

M400 is Monel. 80,000-90,000 PSI tensile. High corrosion resistance.

How's this for a demonstration? Spinning motor from the rear.

Nice write up. Makes it sound great to say da least. I like em alot. Hope he gets it going. When i said "kid" i was using da term loosely. Not any disrespect intended.

Looks like she may have slipped timing. I really think that is the best of all evils. The fix is cumbersome with big heavy casting to remove but it's all in front and does not disturb any complicated components or head. A mechanic came over and they say that the rotor does not return to No. 1 every time. Like we thought we thought it did. He is coming back to check again and do a compression test.
Since it's hard for me to believe a low mileage 305 V6 has a stretched chain or broken gear, I guess it can be bad dizzy gear.

Hey everyone- I wanted to let y’all know, I towed the truck to a reputable local shop that specializes in older vehicles, and restorations.
I told them the whole story, and the owner had a hunch. He pulled the valve covers and we found bent push rods, some disconnected. Only one cylinder with a straight rod and compression.

It appears that when I got the truck running, and drove it for a couple days, I stirred up the separated gas sediment in the bottom of the tank, which acted like glue and locked things up. That was last September, and I’ve been chasing my tail since then.
Huge thanks to Bartamos for going above and beyond to help me, and thanks to all of you for help and insights. The truck will be fixed, and I will continue to learn.
Thanks y’all- Jimmy

Glad to hear you found the problem and your going to fix it!

Bartamos, did you send Jimmy the bill for your opinions? @ .02 cents x 62 opinions = $1.24 as I see it. LOL!

Thanks for the update. Unfortunately you found the common problem with trying to start a long dormant engine. Our Tech Tip covers the proper procedure but hindsight is always 20/20. Good to hear she will live to run another day.

Didn't charge this time. Putting up with me is priceless

I am really puzzled by the shop saying it was old gas "gluing" motor together and bending and breaking valves. I know motors can be locked up/frozen and need a procedure to "loosen". A first start procedure. But this was presented as driven around the block and parked, then won't start. A mechanic knows more that I, but I'm going with timing gear/chain or dizzy gear sent motor into chaos. There is at least one strike against my idea, the motor is a "clearance motor" so piston supposedly would not hit valves. He first had a mobile mechanic say timing was indeed off. I was advising taking valve cover off after one more test, but I backed off when mechanic arrived. Then it was taken to a shop. These were good decisions on Jimmy's part. Mechanic is going to find out that parts are not easy to find I suspect. I'm going to suggest to Jimmy that these motors are available for $200-$500 running. A rebuild can be 1000's from a shop.

Exactly the diagnosis I made on February 26, and wrote up in great detail on Feb. 28.....little or no lubrication leading to internal damage

You da man.