# 400 motor questions



## DRaSTiK68 (May 2, 2016)

Well, finally got the car back from the mechanic. Ended up replacing the starter, radiator (bought a 4 core radiator from Ledfoot Racing), and did some rewiring. Car is running pretty strong. Compression is level across all cylinders (between 110-115), except cylinder 8 (showing 88). Hoping driving it for a little might fix it a little (he said the rings look ok).

My question...I took it out for a drive the other night. Temp gauge never crossed the halfway mark, even idling in traffic, and it was 92 degrees out and pretty humid. Brought the car home, pulled into the garage, and it died. Wouldn't crank, wouldn't even buzz when I put the key in the ignition. I let it sit for a few hrs, then tightened down the battery connections. However, the motor was still hot to the touch, and that was after sitting with the hood open for 4+ hrs. I'm going to attempt to start it this afternoon. What would cause the block/heads to still be that hot after that time?

Car is a numbers matching 68 GTO, 400/4 speed, 51k original miles.


----------



## chuckha62 (Apr 5, 2010)

Seems odd to retain heat that long. 

Your compression is only 110-115 PSI? That's awfully low for a '68. I would expect to see at least 165-170 with no more than a 10% difference between the high and low. How was the compression check done? Who performed it? 

Let us know if it fires up when you give it a shot this afternoon.


----------



## DRaSTiK68 (May 2, 2016)

He ran the compression test when he was going over the motor. I'm not a big motor guy, I know the basics and that's pretty much it. I'll go over the work list he did when I get home and look at the compression numbers (I hope I remembered them correctly). 

What could be the possible causes of the engine holding heat for that long? The car sat in the garage for over 20 years, so he pulled the heads, made sure the crank spun, did all the loose ends, etc. I'm hoping it's not a coolant issue.


----------



## chuckha62 (Apr 5, 2010)

For the record, the correct way to do a compression check is to first pull all of the spark plugs, then block the carburetor wide open (the engine has to be able to pull in ample air to compress), then check each cylinder with four "puffs" only. If it was not done in this manner you will not have an accurate test.

Earlier, you said the temp "never crossed the halfway mark". Do you have an actual number to associate with that? I'm not overly familiar with the factory markings and calibration, as I have an aftermarket numbered gauge in mine. Did you verify a full radiator with adequate flow? Depending on ambient temp, it may have just taken a long time to get all that cast iron cooled back down.

As for not starting, make sure you're in neutral and that your neutral safety switch is working properly. Then, go from there.

Good luck,

Chuck


----------



## DRaSTiK68 (May 2, 2016)

Well, it started and ran with no problems, but even after a short drive, I can't believe how hot the motor was. I'll have to look for the compression numbers when I get back home tonight. The temp gauge has no numbers, but the needle stayed on the "cool" side of the halfway mark the entire time.

As for the radiator, it was filled, but I don't know the extent of the flow. I noticed some slight screeching of the belts at higher rpms, but the tach currently isn't functioning, so I can't tell where it is in the rev range. I'll need to replace the belts sometime in the near future. 

What would cause cooling issues? The fan is still the stock unit that came with the car (from what I can tell). I need to find out what motor I have in the car (400 w/ a 4 speed).


----------



## 60sPontiacs (Jul 14, 2016)

You've got a lot of possibilities with a "new" car, but check your timing - I had exhaust manifolds turn red in a Cavalier that must have been blowing out flaming fuel. 

Does fan have a clutch? If so, see if it's loose - not sure how to tell if clutch locks when it's running, but if it's slipping it won't pull air through radiator at low speeds. I assume you have a fan shroud. Make sure the belts are tight enough. 

Was radiator water rusty? Any sign of coolant leaks on old radiator, like water marks on radiator core? someone could have put in stop leak and clogged up small coolant holes in heads. 

Does it have original heads? See casting number above center exhaust ports. This relates to compression ratio. And if compression is stock, someone could have backed off timing so it doesn't detonate. Might also want to make sure distributor is original and that weights are free, springs doing their job, etc.

A handy tool is non-contact infrared thermometer. Harbor Freight has a cheap one $20. Accuracy may be questionable, but you can tell how much it's cooling down. 
Infrared Thermometer - Non-contact, Digital Thermometer


----------



## DRaSTiK68 (May 2, 2016)

Thank you for the tips. I haven't really had time to inspect or tinker around with anything yet. My mechanic has been working on my cars for 20 years, and has rebuilt several 60s and 70s model Vettes, so I have faith that he didn't screw me over.

As far as the clutch fan, I'll check it this weekend, as well as the belts. They were replaced 5+ years ago, but the car sat for such a long time. 

As far as the radiator, it had no leaks when we brought it to the shop and got it running. When he took it for an actual drive, he got back to the shop and it was leaking, so I just went ahead and ordered the new one.

The heads are original from what I can tell (I was told the motor was never touched), but I'll double check the casting numbers (again, I need to check the block to find out what 400 I have). From what I was told, the distributor is fine.

Again, I'm not a big engine guy. I know the basics, but none of the nuances of Pontiac motors. This will all be a learning experience for me. Thanks again for the help guys!


----------



## geeteeohguy (Feb 2, 2008)

If the heads are original, you should have about 180PSI compression in all cylinders. Was the timing chain messed with? I suspect it could have been installed a tooth off, resulting in retarded cam timing and low compression. Also, you need to get a pyrometer and verify your engine temps compared to the gauge...I suspect the gauge could be inaccurate due to a bad sending unit or gauge. It almost sounds like the engine got hot and seized after you shut it down. Can you turn it over with a breaker bar on the crank pulley nut? Lots of things to start checking here. Also, I have found that MANY compression testers are inaccurate due to faulty schrader valves. Be sure the compression tester is in good shape, or verify compression with another gauge. NAPA sells the new schrader valves for about $2 apiece.


----------



## DRaSTiK68 (May 2, 2016)

The engine started and ran with no problems yesterday, it was just heating up quickly. When it died the other night, I suspected the battery terminals. After tightening them down and letting it sit overnight, it started on the second try. I'm thinking I'm gonna have to chase down a bunch of little things to get this solved.


----------



## 60sPontiacs (Jul 14, 2016)

Yeah, a bunch of little things... I agree with all that's been suggested. I've been working on them for 45 years but have much to learn about Pontiac specifics from guys here.

First have to establish temperature. Sounds like the gauge shows okay, but I don't trust them. You can get a cheap mechanical temp gauge from Autozone ($20) to verify it. Coil up the lead and tie wrap it somewhere under the hood. Pontiacs run kind of hot and there's a lot of metal to cool down so is important to get numbers (accuracy not as important as relative.. how fast it goes up and how long to cool down). If it's REALLY hot, it'll boil over. I read a crude test is spit on the head and if it spits back it's too hot...

It could have stuck thermostat (remove it for testing). And there's a plate with some tubes from water pump to block - either can rust through and cause circulation problems.

You've got one low cylinder (#8 ) - hopefully your memory was wrong about the other 7... Could have a head gasket leaking into water jacket (not sure if this causes overheating). Can tell by pulling radiator cap (when cold) and putting plastic wrap loosely over fill inlet, push it down to make a dimple, then secure with rubberband to form air seal. If you start it (or just crank it over a few revs with coil wire pulled) and the plastic pops up, you've got pressure in water jacket from cylinder. It doesn't take long for the water to rise from expansion(?) with running engine as it heats up so don't let it run long.

Good to pull #8 plug to see what it looks like (less carbon than others can indicate water leak). Could be carboned/stuck rings causing low psi if not head gasket, so could spray something in hole, let it set, see if it loosens, and check comp later (others have more experience with this - not sure if good to spray PB blaster, WD-40 as it may be bad/wash cyl walls if you start it - Marvel Mystery/regular oil may be ok).


----------



## DRaSTiK68 (May 2, 2016)

Thank you! I'm heading to Autozone and Harbor Freight this weekend to pick up a couple tools (can't afford high end stuff yet), including everything that's been mentioned. I also ordered the "Rebuilding Pontiac V8's" book so I'm not headed in completely blind.

This is my first project car, and the more you guys suggest, the more I realize I need to learn.

Thank you again.


----------



## PontiacJim (Dec 29, 2012)

geeteeohguy said:


> If the heads are original, you should have about 180PSI compression in all cylinders. Was the timing chain messed with? I suspect it could have been installed a tooth off, resulting in retarded cam timing and low compression.


First, the 1968 Pontiac manual states the 10.5 & 10.75 compression 400CI engines have a compression of 185-210 PSI at 155-165 cranking RPM's.

Don't forget, these engines also used the aluminum/nylon coated cam timing gear which often times was chipped, cracked, or slap worn out between 60,000 - 80,000 depending on how you drove it. My few experiences with timing chain replacement was that the timing chain was pretty sloppy as well. This will cause a lot of slop in the chain and effect timing. Pull the distributor cap so you can see your rotor. Then rotate the balancer by hand or using a socket/extension/ratchet (if your belts are tight enough & you don't have a clutch fan, you should be able to rotate it with the fan) and observe the rotor in the distributor. The minute it moves, stop. Now make a mark on your balancer that lines up with any timing mark (no you don't have to line up your timing mark, because this test is not about timing). Now rotate the engine in the opposite way and the minute the rotor moves, stop, then put another mark on your balancer. You can rotate the balancer back again to verify/confirm the rotor's movement against your marks on the balancer. 

From everything I have read, more than 10 degrees (or something like 1/2") of movement at the balancer before the rotor moves, means too much slack in the chain and its time for replacement. This website gives tells you how to measure the dia of your balancer, and degrees of rotation at the crank. You won't need the degree wheel as you should be able to use the stock timing tab which has the degree marks/lines already on it. Timing Chain Slack Test


----------



## 60sPontiacs (Jul 14, 2016)

PontiacJim's timing chain test is good - easy to do. If never apart, can almost guarantee yours is loose. First experience with bad one in dad's 67 GP (in ~1972) - mashing the gas pedal caused a single backfire through the carburetor - other than that car seemed to run fine.

While gathering tools,etc you could also get a cheap mechanical oil pressure gauge. I saw no mention of OP in your post. Put under hood now to monitor it - you can duct tape windshield to see while driving, or mount inside car (though might want better permanent gauges). I've had a cheap Equus mini-triple gauge from K-Mart in my 68 Chevy for 30 years and it still works fine after 200K miles. I like both lights and gauges (need 1/8" pipe t-fitting to use both for oil pressure - temp is trickier because of threaded hole into water jacket... may be able to get thermostat housing with tapped hole, making sure sensor end doesn't hit thermostat). Bunch of std size triples on ebay for cheap Triple Gauge Kit | eBay. Advance Auto (same as Carquest now) has this triple gauge for $18. Buy Bosch Gauges 2" Mechanical Water-Oil Temperature Gauge FST 8207 at Advance Auto Parts - Autozone has one for $35 http://www.autozone.com/gauges-and-...-2-in-white-face-triple-gauge-kit/255955_0_0/ (Advance is good because you can get 20% off any internet orders and pick up parts at store in 30 min - 30% if over $50, and $40 off $100 or more - free shipping if over $75 30% off Advance Auto Parts Coupons & Discount Codes 2016 - sign up for Speed Perks and get $5-20 off coupon for next order)

My first car WAS a project car... '66 4-door 326 LeMans ($50 haggled down to $25) - body was straight aside from salt holes rusted through lower rear quarters. It didn't run, so first thing was installing an underdash 8-track for work tunes. Needed points, carb cleanout, etc then drove it home a few miles. Sludge under valve covers was packed in between rockers and there were 3 pushrods in the oil pan. You're steps ahead of that...


----------



## DRaSTiK68 (May 2, 2016)

Awesome. Thank you again for the help!

Tried to start the car last night, it kicked over once, then nothing. I need to replace the battery and cables soon anyway, gonna knock that our next week. Spoke with my mechanic last night, he did the compression testing before the car was running. It was only the initial compression after sitting for 20+ years.


----------



## 60sPontiacs (Jul 14, 2016)

DRaSTiK68 said:


> Awesome. Thank you again for the help!
> 
> Tried to start the car last night, it kicked over once, then nothing. I need to replace the battery and cables soon anyway, gonna knock that our next week. Spoke with my mechanic last night, he did the compression testing before the car was running. It was only the initial compression after sitting for 20+ years.


Always good feeling to have a fresh battery and clean connections. If not done already, also check connections at the starter. A triple gauge will show if your battery/charging voltage is good (easy to verify volts gauge with a digital multimeter, which you can get free [a cheap one] with Harbor Freight coupon).
http://www.harborfreight.com/facebook.html

So were those low compression numbers correct? you said not sure if you'd remembered right. Time to recheck after running it as you have - Autozone by my house will loan a compression tester - I think they all do.


----------



## chuckha62 (Apr 5, 2010)

DRaSTiK68 said:


> Awesome. Thank you again for the help!
> 
> Tried to start the car last night, it kicked over once, then nothing. I need to replace the battery and cables soon anyway, gonna knock that our next week. Spoke with my mechanic last night, he did the compression testing before the car was running. It was only the initial compression after sitting for 20+ years.


Got it. That could very well explain the numbers you posted. It would be interesting to see another compression reading after you have it running better and see what it indicates then. 

As for your engine temp, read through this forum for countless threads (some of them stickied) for pointers on keeping your cooling system functioning properly and your engine from overheating. 

Good luck!


----------



## DRaSTiK68 (May 2, 2016)

Thanks again guys. The starter was replaced a few weeks ago, so I'm hoping that isn't the problem. Gonna swing by Autozone and see if I can rent a compression tester. 

The low numbers I posted before were correct, but I'm dying to know what they are now.


----------



## 1968gto421 (Mar 28, 2014)

On your engine running hot, have you checked the clearance on the water pump divider plate (behind the impeller)? Here is a good thread on how this simple mod has helped with reducing engine temps. 

Chalk up one more for the cast impeller. - PY Online Forums


----------



## BearGFR (Aug 25, 2008)

That's a good trick, using the plastic wrap to check for cylinder leakage --- I'll catalog that one away for future reference.

It's hard to judge how hot "feels hot" is - perceptions of what that means varies from person to person. You might consider getting yourself one of these:
https://www.amazon.com/Mastercool-5...8933893&sr=1-12&keywords=infrared+thermometer
(or something similar) to get some semi-accurate readings. Point it at various places on the heads, especially the coolant crossover at the front of the engine (where the top radiator hose connects) while the engine is stone cold just to make sure the tool is reading accurately, then measure it after you drive it and get it warm, after you drive it to see how long it takes to cool down, etc. (After you drive it and first shut it down, don't be surprised if the temp actually goes UP a little after shutdown. That's normal and happens because the coolant is no longer circulating.) Doing this should also help you determine if you can trust your temp gauge or not.

Others have already suggested good things to check. Your 'not starting' problem can also be electrical (sounds like it might be), especially if those are your original battery cables. They can degrade over time to the point where when they get really hot, so does electrical resistance -- to the point where your starter won't operate at all. Search on here, and google around for 'Pontiac hot start' (and variations thereof) and you'll probably find more information on the problem and what people have done to address it.

Bear


----------



## Goat Roper (Oct 28, 2014)

I now have 3 stock starters sitting on the floor, I tried new cables, new purple wire, rerouting cables and every other fix for the hot start problem.
I finally went with the RobbMc mini starter and that fixed the melting wires/cooked solenoid problem.
With this starter you can rotate the solenoid to the bottom next to the oil pan and away from the manifold.
Finally no more hot start problems.

RobbMc Performance Products - RobbMc Mini-Starters


----------



## geeteeohguy (Feb 2, 2008)

Always check the compression on a hot or at least fairly warm engine with all the spark plugs out, the spark disabled, and the throttle blocked wide open. My bet is that you're compression will come up quite a bit. I am suspicious of a 'mechanic' that would do a compression test on a cold engine after a 20 year sleep. A mechanic worth his salt would simply have done a quick cranking vacuum test to determine if all the holes were ok. Also, as a many-decades-multiple GTO owner-operator, I have never needed anything other than the stock starter and solenoid, headers or not. My no crank issues have always been the result of a bad (high resistance) 'S' wire from the ignition switch to the solenoid. No need for fancy starters, heat shields, remote solenoids, etc. if the original system is up to snuff and operating as designed. My two cents......


----------



## DRaSTiK68 (May 2, 2016)

Thank you to everyone for the replies. I traced the starting problem to the battery wires/connection. They were old and fraying, and are being replaced this week. As far as the temperature issue, a good friend/motor guy is taking a look at the timing next week when I drop it off to him, and he's gonna run another compression test for me. Hopefully the numbers come back better than they were. I haven't had the car out for a drive (no time in my schedule), but it started up just fine when I tightened up the connection at the terminals. Still trying to get my tach to work so I can at least tell what rpm the motor is at.

Thanks again guys. I'll update the post as soon as I have more info.


----------



## DRaSTiK68 (May 2, 2016)

Well, took the car to another buddy to have him check on the motor. He discovered a ton of problems my "trusted mechanic" didn't take care of (rigged fuel lines, battery cable melted to the exhaust, loose wheel bearings, leaking Trans seal, wrong length brake lines, etc. I could go on and on), so it'll be by his shop for a week or two. I'm going back to try and get some money back from the mechanic I'll never be using again.

Buddy said the motor is running a little hot, but he suspects the timing. He's replacing the thermostat and fan for me, so we'll see what the new total is when I get back home. Looks like a total rebuild might be in the future. Hahaha


----------



## chuckha62 (Apr 5, 2010)

I wish I could tell you I was surprised to hear this. Hang in there and hopefully someone who knows what they're doing will sort it out.


----------



## DRaSTiK68 (May 2, 2016)

I've been taking my cars to the guy for 15 years, and never had a problem. He's rebuilt several old Vettes that looked pretty damn good, so I thought it was in good hands. I'm surprised at the shoddy work to say the least.

New guy has built several 400s, as well as quite a few ground up full restorations. I've seen some of his work, and ridden in several of the cars, so I trust him. He immediately found a bunch of stuff wrong, and laid out a new plan. Compression came back much better (190-200 across all cylinders), but I'll need to replace a few gaskets soon (trans seals as well). He ordered a new carb (670 Holley), as well as a fan clutch/thermostat, so the cooling issue should be handled. After getting everything dialed in, we're gonna tackle the suspension, which is totally shot. Got a long road ahead of me. Lol


----------



## chuckha62 (Apr 5, 2010)

DRaSTiK68 said:


> I've been taking my cars to the guy for 15 years, and never had a problem. He's rebuilt several old Vettes that looked pretty damn good, so I thought it was in good hands. I'm surprised at the shoddy work to say the least.
> 
> New guy has built several 400s, as well as quite a few ground up full restorations. I've seen some of his work, and ridden in several of the cars, so I trust him. He immediately found a bunch of stuff wrong, and laid out a new plan. Compression came back much better (190-200 across all cylinders), but I'll need to replace a few gaskets soon (trans seals as well). He ordered a new carb (670 Holley), as well as a fan clutch/thermostat, so the cooling issue should be handled. After getting everything dialed in, we're gonna tackle the suspension, which is totally shot. Got a long road ahead of me. Lol


Sounds like a plan. I have to ask though... Why a 670 Holley? I mean I like them and have used them, but the Quadrajet on your car will render better performance AND economy.

I'm sorry but as soon as someone chooses the Holley (or an Edelbrock, aka AFB) over the Quadrajet, it immediately makes me suspect their abilities. 

Let's see how it goes, as the fan and clutch alone may not resolve the cooling issue. They are the right place to start though, assuming the radiator is known good and flows freely.

Good luck getting it all sorted out and drivable!

Chuck


----------



## DRaSTiK68 (May 2, 2016)

Thanks!

The radiator is a brand new, 4 core from Leadfoot racing, capable of supporting 800 hp, so it should be fine. New thermostat, fan and clutch, water pump, and timing chain/gear are on the way, should be installed by early next week.

Is the stock carb a Quadrajet? Reason I ask is, the gaskets and linkage were in rough shape. He suggested the Holley since he's had luck with them on previous 400 rebuilds. I'm still learning a lot about these motors, so I'm going off his advice.


----------



## chuckha62 (Apr 5, 2010)

Yes, the stock carburetor is the Quadrajet, which is a spread bore (secondaries are larger then the primaries). The Holley 670 (and I may be incorrectly assuming it's the _typical_ Street Avenger series) is a standard bore carburetor and will require an adapter to work on the stock intake manifold. LOTS of old school mechanics never took the time to understand the Rochester Quadrajet and routinely threw them out in favor of a Holley or AFB simply because they didn't understand them and just how good they were/are. A properly set up Quadrajet will nearly always give you better performance, throttle response and fuel economy. 

If you have the original carb, it's probably worth trying to sort out.

That's my $.02 worth anyway.


----------



## DRaSTiK68 (May 2, 2016)

I just spoke with him, he said the bushings in the throttle shaft are all really worn and leaking vacuum. I'm gonna take the QJet and rebuild it on my own (I figure it'll be a good learning experience). Would the Holley still be a decent choice if I ever decide to upgrade the intake manifold down the line?


----------



## geeteeohguy (Feb 2, 2008)

After the Quadrajet, a Holley is probably the best bet for power. Holleys are easy to tune and simple, that's why people like them. Like Chuck said, it's the easy way out for those not familiar with the superior Q-jet. All else being equal, a stock intake with a Q-jet will run all over a Holley equipped car, and get better gas mileage to boot, due to its far more sophisticated fuel metering. I second what Chuck says: any time I see an Edelbrock or a Holley on one of these cars, it tells me that the builder isn't a tune-savvy guy.


----------



## DRaSTiK68 (May 2, 2016)

geeteeohguy said:


> After the Quadrajet, a Holley is probably the best bet for power. Holleys are easy to tune and simple, that's why people like them. Like Chuck said, it's the easy way out for those not familiar with the superior Q-jet. All else being equal, a stock intake with a Q-jet will run all over a Holley equipped car, and get better gas mileage to boot, due to its far more sophisticated fuel metering. I second what Chuck says: any time I see an Edelbrock or a Holley on one of these cars, it tells me that the builder isn't a tune-savvy guy.


I'm following Chuck's advice and rebuilding the Q-Jet. I'll use the Holley in the meantime, I'm getting a pretty good deal on it. Thanks for the input!


----------

