Timing and Cooling Issues

[Dirtboy]

So here's the set up:
85 K20
Newly remanfactured ATK crate 350, 87 up block with 1 piece rear main seal, pre 86 heads
Whatever cam they used, assume stock
Chevrolet dual plane aluminum manifold
New Edelbrock 1406 Carb with fuel pressure regulator and new filter
New aluminum radiator
New T-stat. Edelbrock 160 degree
4 month old water pump and new top/bottom rad hoses

Set the initial timing to 4 deg BTDC w/o vac advance, 650 RPM idle speed
Broke engine in, (2000 RPM for 20 mins, cooled, ran valves and repeated according to manufacturer instructions)

Now the two problems:

At 4 degrees btdc the truck starts and idles great, runs at around 210 degrees but heats up to about 235-240 before dropping back down. Gently easing up on throttle is good but a snap of the throttle produces backfire and stalling. No power in gear, backfires and stalls.

Adjusted timing up to 10-12 degrees btdc and the symptoms got a little better, still not drivable. Cooling is still running hotter before cooling back down to 210

Adjusted timing up to 24 degrees initial, eliminates backfiring, throttle response is good in gear, drives good but truck wants to heat up to 250 before dropping back to 210 then fluctuates 210 up to 230 constantly while driving. No pinging.

Backed timing down to about 18 -19 degrees initial and throttle slightly backfires on snap, backfires and stalls in gear under load, heats up to about 220 before dropping to 208-210 and fluctuates. No pinging.

Adjusted to 21 degrees btdc and throttle/power issues are eliminated but engine wants to run up to 235 degrees before dropping to 210 and fluctuating. No pinging.

Thermal temp gun reinforces what the dash gauge is reading. Truck never overheated. Pump drew down the coolant and circulated, heater works good. The temp fluctuation is frequent and quick not gradual.

Sorry for the long post but having all the info to troubleshoot is sometimes good.

I'm stumped, I think it's a timing issue but not sure. There has to be a guru in here that has seen a shitstorm like this before! Lol

 

[donnieray]

I think your tstat is bad, maybe. I had similar issues with my K10 last summer. I had just installed a new aluminum radiator and a new Mr Gasket 180 tstat and I always test a tstat in a pot of water on the stove before installing. Truck was heating up to 135 and driving me crazy. The tstat was stuck shut. I have it hanging from a sting in my shop still. Welcome to the forum btw and people much smarter than me will be replying soon I'm quite sure.

 

[Dirtboy]

Yeah, from what I’ve read a bad t-stat is quite common.

 

[Frankenchevy]

In addition to the tstat possibly being defective...

I’d pull the truck on a slope or inclined driveway with the nose on the uphill side after driving around and getting it up to temp. Let it cool down in this nose high position and give the tstat housing some light taps with a plastic screwdriver handle for several minutes as soon as you shut it down. Some wiggling of the upper rad hose won’t hurt either.

After it’s fully cooled down, slowly open the rad cap. You may notice the fluid seems lower. That would indicate you had air trapped in the system. Top it up and try again until the fluid level doesn’t change. They also make a special reservoir that goes where your cap normally would, which does this process for you with the truck running; but I prefer the previously stated process.

Other than that, your era of truck should like 8-12* base with vac advance plugged. Make sure you’re performing these adjustments on a warmed up engine. If it’s still backfiring, it’s time to look at something else ie timing gear, valve train and carb.

 

[1987 GMC Jimmy]

160* is a bit cool, and you’re still having issues. Yeesh. I feel like making a list of things I’d check:

• Check to make sure two or more wires aren’t firing the wrong plugs at the wrong times.
• I’d rotate the engine by hand, watch for the distributor rotor to catch, and make sure there’s no slack in the timing set or it didn’t jump timing. There’s an acceptable amount of slack allowed before it’s considered too much, but I don’t know exactly how many degrees of crankshaft rotation have to happen without the shaft turning before something’s considered wrong.
• Are you positive the distributor didn’t go in 180* off or otherwise misinstalled? Rotor’s pointing to #1 at indicated 0* BTDC?
• I wouldn’t throw a wiped cam lobe out the window. Maybe you can ascertain this visually, but the definitive way is to pull the covers and measure lift for each valve while turning the engine by hand.

Unless it’s an air pocket in the cooling system, it sounds like you’ve covered all the bases there.

 

[Dirtboy]

This is why I’m stumped, I for sure set the distributor correctly and you’d think a remanned engine would have a new cam and the timing gears would be set correctly. The original engine threw a rod. So when I pulled that engine I labeled Every wire and hose to include all the plug wires and left them attached to the cap. I’ve rebuilt a couple of these small block Chevys and never had any issues like this. The engine came from Jegs as a long block so I didn’t put the guts and heads on.

 

[Conejo_K10]

Wasn't there 2 different timing tabs [on the timing chain cover] depending on the year? I think there's only 1 harmonic balancer, but having the right timing tab is critical. The fact it's running hot and you're after-firing, [backfire is actually through the carb], indicates the timing is way late. Also when it gets real hot there's the possibility of detonation or ping.

If you have the valve cover off for #1, rotate the engine and intake valve should've just closed as you're coming up on the timing mark. Stop on the mark and pull the distributor cap to verify where the rotor is pointing.

If the cam timing is off that could also be an issue..

 

[donnieray]

I think your tstat is bad, maybe. I had similar issues with my K10 last summer. I had just installed a new aluminum radiator and a new Mr Gasket 180 tstat and I always test a tstat in a pot of water on the stove before installing. Truck was heating up to 135 and driving me crazy. The tstat was stuck shut. I have it hanging from a sting in my shop still. Welcome to the forum btw and people much smarter than me will be replying soon I'm quite sure.

****, I meant 235!

 

[shiftpro]

****, I meant 235!

....

 

[shiftpro]

Yeah, from what I’ve read a bad t-stat is quite common.

Everything is junk now Dirt, except this forum of experts.

 

[shiftpro]

Faulty, incorrect or general fuckery with a head gasket...? If there was a port closed or restricted imagine the air lock drama would step up a tad...no?

 

[olnick]

The stat NEEDS an air bleed hole drilled into it along side the valve area, the stat is closing then no HOT coolant can flow across the sensor bulb so it goes into cooking mode, when enough hot coolant gets to the bulb it opens up again!
Thank you MADE IN CHINA! This is an old problem from way back with cheap stats
Just drill an eight inch hole and the temp WILL Stabalize

OLNICK

 

[WarlVlachine]

160* is a bit cool, and you’re still having issues. Yeesh. I feel like making a list of things I’d check:

• Check to make sure two or more wires aren’t firing the wrong plugs at the wrong times.
• I’d rotate the engine by hand, watch for the distributor rotor to catch, and make sure there’s no slack in the timing set or it didn’t jump timing. There’s an acceptable amount of slack allowed before it’s considered too much, but I don’t know exactly how many degrees of crankshaft rotation have to happen without the shaft turning before something’s considered wrong.
• Are you positive the distributor didn’t go in 180* off or otherwise misinstalled? Rotor’s pointing to #1 at indicated 0* BTDC?
• I wouldn’t throw a wiped cam lobe out the window. Maybe you can ascertain this visually, but the definitive way is to pull the covers and measure lift for each valve while turning the engine by hand.

Unless it’s an air pocket in the cooling system, it sounds like you’ve covered all the bases there.

I would second this. I know that you said everything was labeled and that you've done this a few times. It doesn't hurt to break it back down and start from scratch, take your time and set the distributor back up and ensure the firing order is nailed down.

An air pocket can be a real B. I'd look into that as well.

On big projects its easy to get burnt out or get ahead of yourself, just take your time. It will work out.

 

[Arkansas_V8]

The stat NEEDS an air bleed hole drilled into it along side the valve area, the stat is closing then no HOT coolant can flow across the sensor bulb so it goes into cooking mode, when enough hot coolant gets to the bulb it opens up again!
Thank you MADE IN CHINA! This is an old problem from way back with cheap stats
Just drill an eight inch hole and the temp WILL Stabalize

OLNICK

Jesus christ, an 8" hole? Lol

 

[idahovette]

Jesus christ, an 8" hole? Lol

Yeau that'll do it!!