Recurring Crate 350 Gremlins

[73kay]

Hey Guys,

Here is what I got:
76 c10 w/ Saginaw 3 OTT
stock goodwrench 350 260hp less than 1500 miles on it
mech fuel pump w/ reg on it @ 5.5psi
edelbrock 1406 600cfm carb w/ electric choke
generic HEI dizzy w/ vac advance
E3 Sparkplugs, gotta check the gap, but remember they were good for hei
Init Timing currently: 12BTDC

Issue:

If I floor it or give it too much gas on the road/up a hill/etc I can feel/hear pinging. I have been chasing this for months off and on, so here is what I have done:

1. Verify TDC w/ valve cover off and it matches harmonic balancer
2. Set initial timing to 14 but I have been all over the place to see if I get a difference and I can't.
3. Set Idle screws - while maybe unrelated, my pass idle screw doesn't change the engine at all and might be stripped it feels like.
4. Check sparkplugs and they look good/normal condition
5. Added a fuel pressure regulator
6. Getting ready to replace the damn dizzy bc that's the only system I haven't replaced.


I can only thing that maybe the dizzy springs aren't right and the vacumn advance is off somehow.

Appreciate any feedback. Its a stock crate 350 and I really am not looking for anything crazy just good power w/ economy. I usually run straight 6's so this is my "big block" haha

[B. W.]

[QUOTE=73kay;7988546]Hey Guys,





I can only thing that maybe the dizzy springs aren't right and the vacumn advance is off somehow.

Check these, if the springs are loose / worn it could advance too quickly (can even stick), vacuum advance come into play under a load (climbing hills) I like where your initial timing is set, I wouldn't go less than 10°. Confirm that the balancer / timing pointer is reading correctly (0° on balancer is true TDC) Also, try running super unleaded.

[DieselSJ]

Have you tried any carb tuning at all? Try a metering rod swap to a rod that has a smaller diameter end and see what happens. Have you pulled the plugs to to check if you are lean?

[Kudzupatch]

Most likely your either lean or you have to much timing.... or both.

[PGSigns]

When you are verifying time you need a timing tape or a timing light with adjustability. To see what it has mechanically cap the vacuum advance and see what the timing is at idle, raise the rpm up 500 and check it again. Do this till you get all in on the mechanical advance. This will give you your timing curve. You have to have this to see what it up and also to see what you get when you put a kit in one or swap a new one in. I use a hand held vacuum pump to test what is in a distributor for vacuum advance. I let the engine idle and increase the vacuum a couple of inches at a time till I get full advance and plot the curve. This lets you know not only the true amount of advance but when it will be in. This allows you to adjust the vacuum advance to your engine combination. A drive with a vacuum gauge hooked to the port you are using will tell you the range you are working in to help choose the correct pot.
Jimmy

[cadillac_al]

I always assumed the 1406 carb was jetted for 305/5.0 economy.

[blazer2007]

I think the 1405 is economy,thats what I have

[geezer#99]

Originally Posted by 73kay

Hey Guys,

Here is what I got:
76 c10 w/ Saginaw 3 OTT
stock goodwrench 350 260hp less than 1500 miles on it
mech fuel pump w/ reg on it @ 5.5psi
edelbrock 1406 600cfm carb w/ electric choke
generic HEI dizzy w/ vac advance
E3 Sparkplugs, gotta check the gap, but remember they were good for hei
Init Timing currently: 12BTDC

Issue:

If I floor it or give it too much gas on the road/up a hill/etc I can feel/hear pinging. I have been chasing this for months off and on, so here is what I have done:

1. Verify TDC w/ valve cover off and it matches harmonic balancer
2. Set initial timing to 14 but I have been all over the place to see if I get a difference and I can't.
3. Set Idle screws - while maybe unrelated, my pass idle screw doesn't change the engine at all and might be stripped it feels like.
4. Check sparkplugs and they look good/normal condition
5. Added a fuel pressure regulator
6. Getting ready to replace the damn dizzy bc that's the only system I haven't replaced.


I can only thing that maybe the dizzy springs aren't right and the vacumn advance is off somehow.

Appreciate any feedback. Its a stock crate 350 and I really am not looking for anything crazy just good power w/ economy. I usually run straight 6's so this is my "big block" haha

You must be really sensitive!! LOL!!
You can feel/hear pinging!
I don't think you'll ever feel it but you could hear it (if it is actually pinging).
Likely you've got a slight missfire under those conditions.

You need to rule out timing as the problem. Confirm your timing tab/balancer by using a piston stop.
http://www.crankshaftcoalition.com/w...op_dead_center

But first thing to do is lower your fuel pressure to 4 psi. Your gauge might be wacky.

[68gmsee]

When I've had an engine ping it's been either timing, bad gas or bad or contaminated fuel.

First thing I would check is timing mark to make sure it's at TDC with #1 piston at the top of travel in the compression stroke.

Then make sure the vacuum advance actually works and does not have a leak or binding. I use a hand vacuum pump but in the past I have checked with mouth suction (shouldn't take much to make it moves).

And for grins, try a higher octane fuel to see if helps. Remember that octane is for retarding the fuel ignition to prevent the pre-ignition. If it helps with the pinging than the problem may be timing not advancing properly.

[Dead Parrot]

Did you set the float levels in the carb prior to installation? They are usually wrong from the factory.

Make sure your power pistons are moving freely. If one is sticking down, will cause a lean condition at high throttle.

Vacuum advance should be out of the picture at or near WOT, especially if your advance pot is connected to manifold vacuum. Make sure there isn't some kind of restriction in the hose that is causing the pot to keep vacuum near WOT.

Idle mix screws are out of the picture at WOT.

What rear end ratio do you have? It is easier to lug the engine with a manual.

As a test, set your initial timing to 0 and see if the pinging stays. If it does, might double check the exhaust system for subtle leaks and loose brackets. Several times I have thought I had a motor problem when in fact I had an exhaust system issue. A small leak might not be heard at low power and become much louder near WOT.

[73kay]

Thanks for the comments. Here is what I found yesterday. I have timing at 10 btdc for now. When I really push the gas it almost "feels" more like a vibration than pinging. I have 2 flow master 40s and it's difficult to really hear as well as I'd like, but my engine mounts are new poly and I gotta doublecheck my Trans mount. Maybe that's loose and under load it's rattling. Also I have a shudder engaging the clutch that maybe related with all of this idk. I had the flywheel machined before it went in but anyways. I will reverify tdc and doublecheck my work but with the light yesterday I can see when my mech advance kicks in and when my vacuum advance kicks in. I'll report back tonight.

[68gmsee]

If while accelerating uphill or stepping on the gas without downshifting you hear what sounds like chain rattling that's what we call pinging. As mentioned above it's not something you feel but you can hear it.

Re. vibration when accelerating. I don't believe I've ever experienced that on a manual shift. My daughter's truck had a slight vibration but only when taking off from a stop. It was a bad spot on the clutch plate.

[AcampoDave]

You had the flywheel machined, did you get a new disc and pressure plate too?

[toolboxchev]

Once you find the true Knocking Gremlin you may wish to add one of these:

http://shop.pertronix.com/pertronix-...ription_tabbed

Most of your stock vac advances all came with different operating specs, the Pertronix unit you can spec it to your application.

The best thing about those is that they are Ethanol Resistant Diaphragms. I used to go through a vac advance every 6 months!

[73kay]

Yes I installed a new pressure plate and clutch at the same time as the flywheel resurface.

[GASoline71]

Did you use a dedicated 12v wire from a switched source at the fuse block fro your hot wire to the HEI? If you dropped in the HEI and used the stock resistor wire that was in the truck for the old points style coil, you'll have too much voltage drop for the HEI to function properly.

Gary

[AcampoDave]

Originally Posted by 73kay

Yes I installed a new pressure plate and clutch at the same time as the flywheel resurface.

Seems odd to me that it would shutter then. It should be smooth as silk. Whether or not this is the root of your problem, a chattering clutch is an annoyance. I just redid mine and the difference was night and day. Did your tranny go in easily with the new set up?

[73kay]

I'm pretty sure for 76 hei was stock right? I'll doublecheck my wiring though. I'm at the point where I'll just want the damn thing to run well. Drove it back from
Austin today pulling a trailer and it's definitely pinging. I'm gonna first verify that the dizzy didn't move. The vac advance holds pressure and I can see the mechanical and vac come in at least with it idling and revving it up. So sorry this thread is all over the place but this has been the story of this motor. While I swore I verified tdc, the only logical explanation is that I'm still off. This weekend I got a friend who is gonna do a sanity check for me and take a look.

[AcampoDave]

Just because the mechanical and vacuum advance are visible with a light doesn't make it right. What you're likely getting is too much advance at the wrong time from one or both of them.

[Warrens69GMC]

Originally Posted by GASoline71

Did you use a dedicated 12v wire from a switched source at the fuse block fro your hot wire to the HEI? If you dropped in the HEI and used the stock resistor wire that was in the truck for the old points style coil, you'll have too much voltage drop for the HEI to function properly.

Gary

I don't think this would apply on a 1976 C10

[GASoline71]

LOL... I always tend to think all these questions are for a 67-72... even though I read the entire thread!

Gary

[73kay]

So this weekend I'm gonna get a second part of eyes and verify tdc again. And then set conservative timing at maybe 10 degrees. If that doesn't fix the pinging issue I'm gonna get a new dizzy to rule that whole thing out. It's just weird bc whenever I set it and drive it seems pretty good and then it comes back. I tightened the crap outta the dizzy so that can't be moving. Just frustrating as all get out.

[DieselSJ]

Originally Posted by 73kay

So this weekend I'm gonna get a second part of eyes and verify tdc again. And then set conservative timing at maybe 10 degrees. If that doesn't fix the pinging issue I'm gonna get a new dizzy to rule that whole thing out. It's just weird bc whenever I set it and drive it seems pretty good and then it comes back. I tightened the crap outta the dizzy so that can't be moving. Just frustrating as all get out.

Amazing that you are so convinced that it is a timing issue even though you have verified it a bunch of times.

Pull a plug and read it. Make it ping and shut it down immediately and pull a plug. And get rid of the crap gimmick E3 plugs.

[nikwho]

Have you checked your timing with full advance, at higher rpm?

What machine work did you have done to your flywheel? This could all be an issue with engine balance?

Sounds like there is too many possible causes. Newly machined rotating parts, possible timing issues, possible carb issues. Do you have another vehicle that you could swap carbs with? Can you recreate the issue with the vehicle in neutral, revving with the hood open? Or only driving, with a load on it? This could be that your machine work negatively effected your rotating assembly balance. Could even be a carrier bearing or u-joint issue.

I've had issues setting timing with an adjustable timing light. Particularly cheap ones. They'll give all sorts of crazy readings. On my 305 that came in my '68 GMC, there was definately an issue with where the TDC mark was on the balancer. I finally ditched the timing light and set the timing by hand. Got it running great, re-checked it wth two timing lights and both said that I had something like 42° of initial timing. The engine only ran well where it "shouldn't have". Might need to just play with the timing, if you really think that it's a timing issue. And verify how much vacuum and mechanical advance your getting and where! You could make your own timing tape, in a pinch! Tape around balancer, physically verify TDC. Sure sounds like it could be something out of balance, though. I'd make sure to check u-joints and carrier bearing, if you have one. Quick check would at least rule it out.

I would physically check TDC. Take a thread in piston stop tool, rotate until it hits, up close to TDC, mark balancer/tape, then rotate the engine in the opposite direction until it hits again. Mark this second spot. TDC will be directly between the two marks. If you dont have a timing tape, you can easily make one! Figure out the circumference of your balancer (diameter x pi). Divide that by 72 and it'll give you the distance between each 5° tick mark. So, if you have an 8" diameter balancer (8x 3.1415926 = 25.1327408 ÷ 72 = 0.349" for each 5° of timing.) Make a tick mark every 0.349" and then eyeball the 1° tick marks between the measured marks. Then you can put that tape around your balancer, aligning TDC to your new TDC mark. This way you can find what your timing advance is doing without trusting an adjustable light. Sorry for the novel. Hope you can get this issue tracked down quickly!

[73kay]

Originally Posted by nikwho

Have you checked your timing with full advance, at higher rpm?

What machine work did you have done to your flywheel? This could all be an issue with engine balance?

Sounds like there is too many possible causes. Newly machined rotating parts, possible timing issues, possible carb issues. Do you have another vehicle that you could swap carbs with? Can you recreate the issue with the vehicle in neutral, revving with the hood open? Or only driving, with a load on it? This could be that your machine work negatively effected your rotating assembly balance. Could even be a carrier bearing or u-joint issue.

I've had issues setting timing with an adjustable timing light. Particularly cheap ones. They'll give all sorts of crazy readings. On my 305 that came in my '68 GMC, there was definately an issue with where the TDC mark was on the balancer. I finally ditched the timing light and set the timing by hand. Got it running great, re-checked it wth two timing lights and both said that I had something like 42° of initial timing. The engine only ran well where it "shouldn't have". Might need to just play with the timing, if you really think that it's a timing issue. And verify how much vacuum and mechanical advance your getting and where! You could make your own timing tape, in a pinch! Tape around balancer, physically verify TDC. Sure sounds like it could be something out of balance, though. I'd make sure to check u-joints and carrier bearing, if you have one. Quick check would at least rule it out.

I would physically check TDC. Take a thread in piston stop tool, rotate until it hits, up close to TDC, mark balancer/tape, then rotate the engine in the opposite direction until it hits again. Mark this second spot. TDC will be directly between the two marks. If you dont have a timing tape, you can easily make one! Figure out the circumference of your balancer (diameter x pi). Divide that by 72 and it'll give you the distance between each 5° tick mark. So, if you have an 8" diameter balancer (8x 3.1415926 = 25.1327408 ÷ 72 = 0.349" for each 5° of timing.) Make a tick mark every 0.349" and then eyeball the 1° tick marks between the measured marks. Then you can put that tape around your balancer, aligning TDC to your new TDC mark. This way you can find what your timing advance is doing without trusting an adjustable light. Sorry for the novel. Hope you can get this issue tracked down quickly!

I have a standard Sears timing gun and the flywheel was resurfaced. I installed all new u joints when I rebuilt the truck. So i want someone to doublecheck the timing with me this weekend and trying to get a spare dizzy too but I might have to just bite the bullet and buy one. I'm already gonna pull the tranny and and flywheel and take it to my machine shop and have them
Take a look at it after the timing/dizzy are verified. Then rebuild the carb lol