Grey Motor Head overhaul

[smclaren]

Hey Guys

I need to pop the head off my motor at some stage to deal with some bad juju ...

- Coffee coloured foam in the cooling system (mainly seen on the radiator cap). Photo attached. There appears to no water in the engine oil .. even after the run down and back to Temora.
- Loosing significant coolant from the radiator overflow. It's not over-heating and runs constantly at around 60-70deg Celsius.
- Some low compression values in a couple of cylinders. Note that I am using a crappy el-cheapo tester here ... so it's the trend I'm looking at.
1. 100. 2. 100. 3. 92. 4. 95. 5. 98. 6. 100
- Noticeable miss at idle, flat spot on take off, starts breaking down at >65mph.
- Tricky to start until at operating temperature.
- Super fumy exhaust (Currently running it lean to see if that helps here. Doesn't seem to)
- Valve stem seals are in desperate need of replacement, whilst the head is off.

I'm hoping the fix is just a new head gasket and have one of Harv's improved versions lined up.

Keen on any thoughts on what beyond the head gasket and valve stem seals is worth doing at the same time ? Obviously will check the valves & seats for any pitting/burning/build up etc. but are there any jobs or simple component updates worth considering ? Not really looking for any performance mods unless its a simple component upgrade.

Please let me know your thoughts.

Steve

[ardiesse]

Steve,

Executive summary: Don't take the cylinder head off yet. Do all you can to fix the miss at idle and the hard starting first.

- The coffee-coloured foam is rusty sludge. Go to Bunnings and buy a two-kilo bottle of Diggers Rust and Stain Remover (warning: oxalic acid powder. Poisonous, very effective bleach. Don't get it on your clothing). Drain the cooling system with the engine hot. If no water comes out of the drain cock on the LHS of the crankcase, remove the drain cock, and shove some coathanger wire into the hole, working it around until the mud begins to flow, followed by coolant. Put about a cupful of oxalic acid in your cooling system, take the car for a long drive, then drain and refill cooling system. Repeat as often as needed.

- Losing coolant: Sludge in the cooling system makes the radiator cap leak, but slowly. Get the engine up to operating temperature and fill the radiator brim-full with the engine idling, until no more bubbles come out. Then give the engine a good hard rev. If lots of bubbles come out of the water, and it happens every time you rev the engine up, you have either a leaking head gasket (moderately bad) or a cracked cylinder head (catastrophe).

- The (small) variation in your compression pressures is no cause for alarm and suggests that your head's not cracked. I've run grey motors for years with more variation in compressions than yours.

- Find out which cylinder has the miss at idle. Short out each spark plug in turn with a screwdriver. Or unplug and replace the HT leads one at a time if you have boots over the spark plugs. The bad cylinder will be the one with the least noticeable change of engine note on shorting out the spark plug. Does the bad cylinder have lower compression compared with the others?

- The breaking down above 65 mph may be due to over-advanced ignition timing. Start engine and gradually increase engine speed. If the engine starts to stumble and fluff at a couple of thousand rpm, the ignition timing's too advanced. Retard the timing until the engine runs smoothly. Another diagnosis is if the car hunts and surges on light throttle openings at 50-60 km/h in top gear.

- Hard starting is frequently caused by the choke not operating properly. Make certain that your choke closes all the way when you pull the knob out. Straighten kinks in the choke cable and adjust the outer cable in the clamp so that you have the full range of movement in the choke lever.

- Fumy exhaust: Steamy or smoky? Does your exhaust smell of burnt oil? Does the car blow smoke? If you take the oil filler cap off with the engine running, do fumes come out the rocker cover? If yes, yes and yes, you probably need to replace the piston rings. Head's gotta come off for that. And you can flush the cooling system passages out while you're at it.

Check for Leaky Valves: Take the manifolds off. Turn the engine over by hand until number 1 is beginning its compression stroke. Spray a good burst of WD-40 into the exhaust port. Turn the engine over through the compression stroke. Can you hear hissing or bubbling sounds coming out of the exhaust port as you do so? Repeat the procedure for the other five cylinders, taking care to get the WD-40 onto the correct exhaust valve head for cylinders 2,3,4,5. Use the red tube on the pressure-pak. If you hear hissing or bubbling sounds in any of the exhaust ports, that indicates leaky exhaust valves. You may now take the cylinder head off.

- Valve stem oil seals in grey motors do not usually give trouble. The early grey motors don't have them at all. Excessive oil consumption is caused by piston ring troubles first and worn valve guides second.

If you're going to pull the cylinder head off, replace the piston rings while you're at it. And while you've got the pistons out, it's a shame not to replace the bearings. And if you should discover that the camshaft still has a fibre timing gear, well, now's the time to replace it. And things start getting out of hand . . .

Rob

[Errol62]

Great summary Rob


Sent from my iPhone using Tapatalk

[smclaren]

Plenty for me to look at there, Rob ... I really appreciate the in depth response and info.

I'll do some diagnostics and report back.

Steve

[Blacky]

The oxalic acid does a good job , I have used it in the past

[EK DAZ]

Also check the condition of the frost plugs behind the side plate. If these are leaking they will allow coolant into the oil.

[ardiesse]

The Interstate Grey Motor Diagnostic and Tune-Up Service made a visit to the Sunshine Coast earlier this week.

Here's what I found -

Turning the engine over by hand suggested that the compressions were good, with the possible exception of number 4 being a little low.
The choke was slightly out of adjustment but otherwise in good order. I straightened the inner cable and readjusted the choke.
The car started easily but had the classic irregular miss at fast idle characteristic of over-advanced ignition timing. I retarded the timing bit by bit until the engine ran smoothly at 1500-2000 rpm.
WD-40 around the carburettor base and inlet manifold legs showed no evidence of vacuum leaks.
I reset the idle mixture and speed to suit the timing settings, and things started to look promising - the engine idle was very good.
But - big flat spot when snapping the throttle open. There was no pump squirt.
Carburettor off. The pump plunger was a loose fit in the bore and didn't seal. It was a spring-loaded leather type, in good condition, so I got my thumbnail under the leather and expanded it. Now there's a good pump squirt. Carburettor back on, and the flat spot largely disappeared.
Still inclined to run a little lean off-idle, so I took the air horn off to check the float level, which was quite low. I bent the float arm bit by bit until the float level was a good eyeball 16 mm.

Pause for lunch at a nearby pub. The wagon drives well. It's torquey and responsive for a stock grey. Told Steve I'd be happy to jump in and drive it back to Sydney.

On return from lunch, I noticed that just off-idle the mixture leans out significantly, to the point where the engine would sometimes stall. I reckon there are problems with the idle ports not being uncovered early enough - positioning of the throttle disc may not be right.
Blowby check from the oil filler: not a problem. Both my Humpy and my FC have more blowby than this motor.
Yes, it blows a puff of smoke off the line at traffic lights.
My verdict on engine condition is - it's in pretty good health. Just drive it until something major goes wrong, which will be a long way off.

Anyway, I left my "known-good" carburettor with Steve to swap over and see whether the off-idle flat spot goes away. Meanwhile, I'll re-read Drew's posts about the troubles he had synchronizing his twin setup.

Rob

[Harv]

I reckon there are problems with the idle ports not being uncovered early enough - positioning of the throttle disc may not be right.

Blade would need to be tilted so that the idle transfer holes are already uncovered at idle. That’s a pretty big throttle opening if the car has good vacuum.

Could be the idle transfer holes are plugged?

Cheers,
Harv

[ardiesse]

Idle transfer holes plugged or restricted sounds right. I found Drew's thread on sorting out a twin setup and his problem was the opposite to Steve's: too rich at idle.

Rob

[smclaren]

Thanks for the visit and your expertise, Rob.

It's a real bonus to hear that the various symptoms didn't amount to my erroneous guess of a head gasket issue. Phew ....

I concur that the carby is most likely the issue producing that very odd miss. I''ll throw your spare carby on asap and report back with results.

And thanks for offering to give my Air Chief radio a look over ... it's way past time I installed it. It's been in that box for 20yrs.

Thanks again, Rob ... you're welcome back any time mate.

Steve

[Harv]

G'day Steve,

What we suspect is causing your stumble from idle are the two upper idle transfer holes. When the carburettor is at idle, fuel is fed from a little hole in the throttle body, below the throttle plate (in line with the brass idle needle valve). You can see this as the fuel squirting in from the picture below, to the left:

idle discharge holes.png (292.08 KiB) Viewed 511 times

When you begin to accelerate, the car needs more fuel. Initially, the carburettor fuel pump plunger puts a squirt of fuel into the carb throat. Rob repaired your plunger leather cup, so now you are getting that squirt. Once that squirt is over, the throttle plates are open a bit more. This uncovers another two holes in the throttle body (the idle transfer holes), a little higher above the throttle plate. These holes start flowing, as per the image above right. That little flow of fuel tides you over until the main jet starts flowing.

We suspect the two upper holes are blocked, or partially blocked. You could bend up a bit of fine wire and give them a gentle probe - the idle transfer holes are #56, #64 and #70 drill (0.0465", 0.0360" and 0.0280”) diameter. Put a piece of string on the end of that wire... so that if you drop it, you can fish it out of the carb throat.

To really confirm those three holes/passages are clear, you take the main body off the throttle body, and blow compressed air down the hole labelled "idle fuel emulsion to throttle body" in the photo below:

throttle body hole.png (105.38 KiB) Viewed 511 times

You should be able to feel compressed air coming out each of the three holes with your finger tips.

Cheers,
Harv

[smclaren]

Thanks Harv

That's a really great explanation of the very low end fuel delivery. I'll definitely clean those transfer holes out.

So for yours and especially Rob's info ... I swapped out the carbs today while Bathurst played in the background, and got some great initial results.

First start very promising --> https://www.flickr.com/photos/193523216 ... rHH0vjCqLD

Highlights ....

- Smoother mechanical pedal. I had a couple of issues that have been resolved by Robs carby, due (I believe) to slop in my carby's throttle plate shaft. Initial pressure on the accelerator could be stiff, this has been resolved. This was really exacerbated by the lack of accelerator pump ... creating a bad flat spot followed by a fuel dump when trying to get past the stiff accelerator moving. An awful driving experience. Added to this was an issue when slowly returning to idle, the idle screw point didn't interface well with the bronze cam (again, shaft slop). So the return to idle would stop at a slightly higher idle position and would require a tap on the peddle to get back to true idle. Rob didnt get to experience those two issues as I had recently lubricated that shaft ... but over time it would slowly go back to the problems as described above. Rob's carby is mechanically heaps smoother ... very nice.

- Smooth acceleration and running ... right across the range, right up to approx 70MPH, when it starts breaking down, but does recover and push through up to almost 80mph (where I chickened out). My old carb would breakdown at 65mph and not recover even when pushed further. I'm guessing this might be a jetting issue ?

I still have a noticeable mis ... it's bit hard to hear it in this video over the clattering mechanicals. You can probably see it better than hear it .. the slight shudder on the motor. Doesn't seem to affect the running of the engine. I'll try and capture a better video of the mis for your consideration. Maybe I should stop calling it a "mis" and probably a "rough spot" ? https://www.flickr.com/photos/193523216 ... 182LN5876Y

There s a few more things I need to check (timing, plugs etc) but all in all, a much better/smoother response and driving experience ... so a definite win.

Interesting side note with Rob's carby, my fuel filter doesn't drain back into the tank when the engine is stopped ... stays full. Hmmmmmm ...

I'm still keen one of those reconditioned carby's you have stashed under the house, Harv .. when you can get back under there of course.

I'll PM you Rob about returning the "brazed" carb back to you ... and thanks again for the lend.

Cheers

Steve

[Harv]

If you have your right boot into it, and it breaks down at 70mph then recovers, its unlikely to be jetting. The main metering jets and power bypass valve are flowing well before 70mph, but should not break down.

Be grateful the glass fuel bowl stays full. It means the needle and seat are tight, and there are no leaks in the fuel lines. This makes for easy starting. The cars that drain the glass bowl often have to crank (...and crank... and crank...) to fill the fuel bowl before firing.

Getting closer to getting under the house. Builders got the slab laid, and steelwork is starting to be delivered.

Cheers,
Harv

[ardiesse]

Steve,

Bit by bit. My cars tend to surge and misfire at high speeds (say above 75 mph). My current thinking on this is that there's too much ignition advance at high engine speeds. So if you don't mind running a couple of tests for me:

- Disconnect the vacuum advance pipe at the distributor and take the car for a fang. See whether it stops missing at high speed. And if the improvement (if any) is still partial, then

- Retard the ignition timing bit by bit with the vacuum advance disconnected until the high-speed miss goes away.

If you can stop the high-speed miss by either of these tricks, good. It means that there are some adjustments to make with the distributor's advance profile, which we will get to as needed.

Back to your carby. You say that the throttle "feel" is much improved with my Frankenstein carburettor - the initial "stiffness" on opening the throttle is gone. This says to me that your throttle disc isn't properly centred in the throttle body. If you're feeling brave, separate the throttle body from the rest of the carby and loosen the throttle disc screws about a quarter-turn. The throttle disc should now be loose enough to move around. Remove the idle speed screw and gently move the throttle disc around in the bore so it doesn't bind when the throttle's closed (hold the throttle body up to the sky and look for a minimum of light shining around the throttle disc) and re-tighten the screws.

Or drain the fuel out of your carby, wait for a few days until it doesn't smell of fuel any more, package it well in a big box, send it down to me and I'll get it sorted.

Rob

PS - the "tin-can" Bosch coils are not above suspicion. You could also try swapping your coil with a 12V, non-ballast-resistor coil like the GT40. Just to eliminate the coil as a source of trouble.

[In the Shed]

Hey Rob,
Some great notes for Steve and others on a very planned & methodical approach to checking grey motors to chase down those niggles. Thank you

Regards
Stephen