Head Gasket Leak

[ggunder]

The 2000 head is all ready to lift off the block and is even unstuck. I supported the cam gear per the manual on the upper timing chain guide which has a small L-shaped bracket for this purpose. Since the engine has head studs, the head has to come straight up during removal. This causes a problem with the upper timing chain guide which interferes with the driver's side of the head where it bolts to the cam tower. Do I just pull harder and rock the head to work it past the tight spot?

I read a tip on page 49 of the Datsun Roadster Book Part I to remove the L-bracket to avoid it breaking off from vibration/metal fatigue and dropping into the timing chain. Any opinions on that idea?

It is like Christmas in my garage! I found a micrometer and a vernier caliper in my father in law's tools, so once the head is off I can measure it.

Thanks for your help! I need to get this out of the car and diagnose the problem.

[Gregs672000]

1) It is possible/likely that the head will not come off with the studs in place so do everything you can to remove them... try double nuting them to see if you can get a wrench on them to get them to loosen and come out. That's been my experience anyway. The studs are made to float, not be bottomed out and snug/tight.

2) Cut off (ya, that is what I said) the Evil-L, or at least check it for fatigue and knotching from the chain hitting it. If it is knotched it has got to go before it goes through your hood! The chain can be supported using a small wood dowel or triangled shaped piece of wood that fits between the chain (in the middle between each side of the chain, understand?) and pressing/pinning both sides up against the chain guide so it doesn't fall into the engine, then remove the cam sprocket (ALWAYS mark your chain to the sprocket with paint or a permanent marker so you can be sure to keep it in time). I made one from a paint stir stick, short enough to fit below the cam sprocket.

If something is not clear, please post again as you do not want to drop the chain or screw up your cam timing... bent valves would be the result of being 1 tooth off.

p.s. After it is put together, be sure to turn the engine by hand with no spark plugs in it to make sure there is nothing hitting or interfering, like valves hitting pistons, especially since your head is cut.

[ggunder]

Thanks for the advice to remove the studs. Upon closer inspection they have an opening to accept an allen wrench. They came right out and allowed the head to be removed without trouble.

Here are the results of wrenching a good part of the day (also oil change on the trusty Integr).

Datsun Head 006 resized.JPG

Datsun Head 002 resized.JPG

Datsun Head 003 resized.JPG

[notoptoy]

Nice work, glad it all came off OK. That is an unusual looking head gasket, is that all copper?
The number 2 and 3 cylinders, and piston tops are very interesting, those are really odd burn patterns.
Let us know the dimensions and how out of true it is.

[fj20spl311]

It looks to me like you have been leaking coolant into #3 for a short time because of the clean piston top and the cleaning around the exhaust. Steam does a good job of cleaning the inside of the combustion chamber. There is a lot of oil build up and the #1 cylinder was running cold (miss-firing?). You might want to replace the rings and hone the cylinders. Did you do a leak down test? Did they replace the "Datsun" valve seals with "Chevy" type seals?

[notoptoy]

Did they replace the "Datsun" valve seals with "Chevy" type seals?

Phil:
Why is this a recommendation, and what is the advantage. Is this recommened on the 1600 as well?
Tom

[fj20spl311]

Phil:
Why is this a recommendation, and what is the advantage. Is this recommended on the 1600 as well?
Tom

It was a question because of all the oil residue in the combustion chamber (rings or guides?).

I have used positive seal valve seals (the typed that need the valve guide machined) with success in the past.

I would also recommend some reading on copper head gaskets and getting in touch with the manufacture of this head gasket as to the proper spray sealant. Hylomar or Copper Kote are the usual suspects. I prefer Hylomar.

[Daryl Smith]

Is it just me? Or is the #3 exhaust valve burnt out?

Was a compression or leakdown test done?

[ggunder]

I did not do a leakdown test since I was pretty sure it was a head gasket problem. The #3 exhaust valve is actually missing a small piece from the edge. I measured the head thickness as best I could with a caliper at the four corners:
Pass. Rear 4.483"
Drivers Side Rear 4.485"
Pass. Front 4.460"
Drivers Side Front 4.465"
So it appear that front to rear there is a 0.025" difference in head thickness.
Frankly I don't know what to do since I can't repeat whatever error was made previously since the engine rebuild was so recent. I guess I need at least some new valves and maybe a whole new head. Hopefully I can use most of the previous parts except some valves and seats?
Thanks for your help on this. Today was perfect roadster weather.

[notoptoy]

I thought that I was seeing a hole in that valve, but chalked it up to carbon build-up and the photo. So then that leads to my second thought, is the top of the corresponding piston burnt? It looks like it?
If you have one valve that failed, I'd have to be suspect of the whole lot. If the top of the piston is burnt as it appers, you'll probably want to replace that too. There is no doubt why it was runnign poorly!

[spyder]

The head's #2 does not look too bad but the picture of the piston in the block looks troublesome. I'm not sure I have a good enough picture to tell if the piston is damaged. I would clean it off to see what shape it is in. Cylinder #3 does look like it has had coolant in it. Did a sudden introduction of coolant damage the exhaust valve?? The exhaust valves are cooled by their time on seat. Is it possible the valve lash was too tight? If the head is cut too much and the compression is too high you might experience pinging or knocking. Not sure if that would damage the valve. Rings seem to be more vulnerable. Timing might mitigate this issue along with enriching the fuel. I had a test head which was cut too much and placed the valves too close to the flat top pistons. Sometimes it would knock hard if I lugged it at low rpms when hot but had lots of power. I missed a shift and bent a couple of exhaust valves. Went back to a more normal thickness head with domed pistons with valve reliefs.

[Gregs672000]

What a bummer, after the motor was rebuilt and all... very disappointing I'm sure. Detonation will quickly melt a piston since the aluminum is the lowest melting temp metal in the mix. Burnt valve would be caused by improper lash not allowing it to seat in the head and transfer heat. A head cut that much will continue to cause problems I fear. As painful as it can be financially, it would likely cost less over time to get a better head, or work very carefully with an expert on how to make this head work and seal properly with the copper gasket. I bought two bare heads off ebay years ago, one of which I know is cut a lot, the other looks a lot better but I have not had it looked at. It would need everything I am sure (seats or at least cut, valves, rockers, seals, springs etc., but it is clean). You could likely use most of your valves assuming they were good in the first place (who knows what was put back in). If you want to consider a different head I could have my friend (head guru) take a look at this one. I'm in no rush to sell it but I'm also not looking for big $$... it's just sitting in my shed for just these reasons. You would have to be patient cause it will take a bit to have it looked at, and I have no idea what shipping would be. PM me if you're interested.

[K1200 GT]

It looks like to me that your head gasket was leaking almost from day one. The extra holes in the head gasket in picture one at the top show signs of black combustion marks at # 1 & 2. While the three extra holes over the 2 & 3 cylinders are clean. Coolant leak there or...? Also a burnt valve can be caused by an exhaust leak at the header pipe. Cold air getting into the hot combustion chamber. So make sure you use a good exhaust gasket and check your header pipe for flatness. IMHO

Richard

[fj20spl311]

I have a concern about this area. (green circle)

Does the head gasket stick into the chamber?

Is there a corresponding mark on the piston top?

What caused this?

[ggunder]

Here are a couple of observations:

The tops of the pistons in all the cylinders appear to be in good shape. The deposits will wipe or scape off pretty easily.

The head gasket does on protrude into any of the cylinders.

The marks on the head as noted in the previous post will wipe off.

Thanks to all for the diagnostic advice. I will post on progress since my son is coming to visit on Mar. 18 and I want this vehicle to be running.

Gary