MGB & GT Forum

I have the head off my 78 Roadster and am about to buy a new head (old one's cracked). Before I put it on, I'd like to determine whether the piston rings need replacing.

I just did the test where you fill the cylinders with WD40 and see how long it takes for it to leak through. I'm not sure what's normal. It took about an hour and ten minutes on the #1 and #3 cylinders, and about an hour and a half on the others. Obviously I'll have to change my oil after this.

How long should this take?

I did that with my engine and the fluid ran out in about 20 minutes.

---

Bill Hines
1966 MGB Roadster

wmhines Wrote:
Thanks Bill - was the engine shot or was that a decent-condition engine?

Maybe an hour's not so bad. I seem to remember a four hour benchmark somewhere but must be misremembering.

Daniel

I have the engine sitting on my garage floor and I am getting ready to take it apart. I have no idea if it has been redone in the last 40 years but its going to get it now. John Twist has some Youtube videos about that subject and he will respond to an email. University motors.

---

Bill Hines
1966 MGB Roadster

Wait, what is this test?

---

"Since the creation of the Internet, the Earth's rotation has been fueled, primarily, by the collective spinning of English teachers in their graves."

"Keep in mind that free advice can frequently be worth less than you pay for it."

In one of John Twist's videos a fluid, he used gasoline, is poured into the cylinders and if the rings are bad it will quickly drain out. You can also do this with the head pouring the fluid into the valve area and if the valves are bad it will drain out. If I can quickly find the link to the video I will attach it.

---

Bill Hines
1966 MGB Roadster



Edited 1 time(s). Last edit at 2008-07-16 09:03 AM by wmhines.

Or you could just use a leak down tester and find out exactly how much percentage of leakage you have, even which valve, if it's valve leakage and exactly pin point the source of the linkage, even rings and how much leakage and not take a chance of catching you or the car on fire with this mickey mouse test. Oh and I did I mention you can buy a leak down tester from HF for $29.99.

OK, whats next, how to build a engine with a adjustable wrench

---

Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com



Edited 1 time(s). Last edit at 2008-07-16 10:25 AM by Speedracer.

Speedracer Wrote:
I would too, but he said that the head was cracked. Wouldn't that affect the readings?

Edit- he also said that he was using WD-40. Never tried lighting it. Is it as flamable as gas? I know when you spray it into a flame it will ignite, but is it the WD-40 itself or the propellant?



Edited 2 time(s). Last edit at 2008-07-16 10:39 AM by alex77.

Would depend on where the crack is. I've never heard of this type of "leak down test" WD 40 certainly isn't as volatile as gasoline but I can't imagine this as a very accurate test procedure. Unless this engine was using a lot of oil previously, I'd put the new head on & go from there. It could then be properly tested for leakdown and if you do want to go into a rebuild, it all has to come out anyway. Pulling the head back off at that point isn't a big deal.

Most cracks on MGB heads are from the water jacket to the outer casting, meaning you normally see coolant leaking, but you could have a blown head gasket leaking form a water jacket to cylinder for example (white smoke out the tailpipe) and that would not be visable from the outside of the engine. The proper test for checking for a coolant leak, with the head on the engine would be a pressure check tester, it screws on your radiator or exapansion tank much like your radiator cap does, has a hand pump, you pump up, and gauge to watch to see if it holds pressure, it would not only check for a crack in the head, but any breech in the cooling system.

Here's the main deal, once you spotted an exhaust valve sunk down into a seat in the head, it really doesn't matter if it's sealing or not, the train of diaster is already headed down the tracks, and that has to be fixed with new hardend exhaust seats, sealing or not.

---

Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com

Thanks everyone for the feedback - I realize that this is somewhat of a mickey mouse test as Hap put it but I was trying to get a rough sense of whether the rings were intact or not and that seems to have worked.

John Twist's video seems to indicate that 15 minutes is ok, though he's using gasoline (nuts!) which is thinner than WD40.

On to the head, then. I found a guy who claims to have a decent condition second-hand bolt-on ready one for $150. Hope it checks out.

Thanks again. I'll run a real leak down test eventually but will need to get a head and air compressor first.

And Hap -- I did my first spark plug change with an adjustable wrench -- so you're got me pegged about right. Not an experience to repeat.