My '84 944 just blew its head gasket so today I tore it open. I'd like the advice of the experienced on what other work I should do while I'm doing this. Last time I did a HG job I got a little carried away and ended up doing rings, rod bearings, pickup, pan gasket, BS housings, etc. I like getting carried away.

Well, this engine has about 180k miles. I did a compression and leakdown test before opening it up. The HG was blown on cylinder 4 so I didn't even bother trying to test that cylinder. My leakdown tester is an air pressure regulator from Home Depot set so that when I connect my air blower the gauge reads 0 psi with the blower open, and 100 psi (from my compressor) with the blower shut. The regulator connects to the hose of a bastardized compression tester. My compression tester is just a standard unit from Kragen.

Cyl 1: 175 psi / 14% leakage
Cyl 2: 174 psi / 8% leakage
Cyl 3: 175 psi / 7% leakage

I don't remember how much oil it consumed, but it was too much. I'd have to add a quart every time I borrowed it, which was about once or twice a month.

This is what I am already planning to do:
everything included in the HG kit
air/oil separator o-rings
oil cooler seals and o-rings
new belts (did the belts, rollers, seals and WP 5 years ago so this time it's just the belts)
I might send out the injectors for rebuilding
Considering new plugs and wires
head job (deck it, new valve guides, 3-angle valve job)

These are things I want to do but I know are just crazy:
BS housings (I can't tell if they're leaking or not, there's just gunk and grime everywhere)
pan gasket (definitely leaking)
while the pan is off, rod bearings
while the rods are opened and head if off, rings and wrist pins



Please chime in and tell me what else I should do while doing the HG job. Also talk some sense into me regarding going overboard.

 

Vacuum lines

 

you know youre going to end up rebuilding it anyways...so you may as well buy the full kit

 

Hmm...

So do I try that DIY cylinder lapping from that other thread? One limitation for me is I don't want to remove the engine from the car, so I won't do the main bearings, and no machinists. Is there anything wrong with that?

Another thought I had was to just bolt this one back together, pick up a spare 944 engine for like $300 and rebuild that one, and swap. Another can of worms, that is.

 

Go for it man and do the whole 9 yards. Once you get the head off you can check the cylinder walls for scoring. The head will have to be trued, valves ground and new sleeves. Belts and rollers or do you feel lucky? Front engine seals. You have to pull and clean the oil cooler, new seals there. Do you have the cooler alignment tool? You are doing the AOS Seals don't forget the Dip Stick Seal. Use Permatex Grey High Temp Sealer at the front and rear of the oil pan, plus at the rear cam housing cover to make it leak free. DO NOT LAP THE CYLINDER WALLS. Leave that Carbon Lip at the top of the cylinders. Might not be a bad idea to pull the radiator and have it prof flushed out to get out all the old crud. If you have not already done so, Replace the old FUEL LINES. They are a Fire waiting to happen at the worst of times. Dang, if it doesn't give me a flushed feeling spending your money for you.

Cheers,
Larry

 

Want a little more HP? You said you like to "While I'm at it" (my famous last words as well)
In a nut shell:
While the head is off and before it goes to a machine shop, why don't you port match in the intake and exhaust manifolds and match the throttle body as well. Even a basic de burr the roughest edges/casting marks of the intake and exhaust. A minor polish of the exhaust side is easy enough to do yourself. If your adventurous, polishing the combustion chamber can reduce the risk of "hot spots" that can cause detonation. I can't detail any combustion chamber reshaping or valve relieving as I have not had any detailed looks of a stock cyl head, but I'm sure there is room for improvement. (Give me a Datsun Z car cyl head and it would be a different story)

If you can do the work yourself, it would be free hp, and at a minium could improve flow and throttle response, and some minor gas mileage improvements.

That is what I would attempt "while I was at it"

Good luck with your project!

 

do the head refresh, everything you listed on top, check your coolant hoses and vacuum lines and the heater control valve. If your injectors haven't been cleaned since new it would be a good idea. Spark plugs yes (they're $2 each and you have them out anyway!) and wires are a maybe...what's on the car now?

You could throw a dash cam at it--those fly around for sale a lot. extra exhaust lift/duration.

 

Thanks Larry. Dipstick o-ring - good one. Roger on the gray silicone. Why should I not lap the cylinders? Are you saying I should just slap on new rings and put the pistons back in? And why leave the carbon ring at the top? The radiator is only a few years old. Fuel lines are a great idea.

is this something I could do with, say, a dremel? I'm with the school of thought that roughness in the runners and ports retains a boundary layer of air, and if I polish the metal it will either slow down the air or do nothing. What do you think? Polishing the CC - never heard of that one. Any downside?

the hcv is only a couple of years old, I think I changed that hcv hose too. I'll check the other hoses/tubes. The car has oem plug wires and they look kinda old. I think I'll keep the stock cam because this car is just a DD and I have other cars where the money:hp ratio is better.

 

my opinion - pull the motor- the amount of time spent supporting the motor, working under the car, trying to get to things you cant, you could have the motor out and back in by then. This would give you access to the clutch, rear main, balance shafts and anything else. I refuse to do much work on a motor without pulling it out.

 

+1

 

A dremel would do the job. You don't want shiny smooth on the intake side, but the roughness of a factory casting is too rough and some transitions are not ideal for smooth airflow.

The exhaust side is another story. Shiny smooth is good for flow, and does not leaving anything for exhaust debris to cling on to.
These are some old (15years ago) pics I have from one of my cyl heads. I can't recall how far into the process the close up pic is, but can give you an idea of the level of polishing that you want to get to. The first pic is of all the major parts after all work was completed. Rods and crank were all lightened, polished, shotpeened and balanced The cyl head was ported/polished, valve area (not combustion chamber) was relieved and transitions where smoothed then polished. Combustion chamber had some minor welding, and the areas around the valves and sparkplug were reshaped and polished to improve intake combustion and exhaust flow. Head was shaved slightly to increase compression, valves were reshaped and polished as well. This resulted in a 10.5:1 compression 2.9l Datsun Z engine producing about 100 hp per litre to the wheels with a 8000rpm redline. Basically a race engine. (triple weber DCOE 44's with 38mm chokes) for the intake in case anyone is interested.

 

Use solvent and small aluminum wire brush to clean top of cylinder walls and deck after head is off! Double check very carefully to make sure that head gasket failure did not crack or burn a hole in the top of blocks deck on cylinder!

If the cylinder walls have no gouges or large scoring and scratching and if the pistons skirts have no marring then I have had good luck with new cheap Deves rings from Pelican breaking in fine and then the motor does not consume any oil anymore?

Of course a rebuilt cylinder head is in order with valve job, deck and new guides and seals!

good luck

 

I paid $55 shipped from a guy on Pelican for the cam, lifters, cam tower, distributor adapter and rear cover. If it's worth 5hp that's only $10 per. I'm not suggesting some wild piece that won't idle--just the factory update. Turbo cars came with the old cam, and I should see a mild bump from the improved exhaust flow. You'll have it off anyway...

 

Can I get some comments on cylinder 4:









The black marks are right below where the HG failed. The brown staining / ring marks look weird, I'm clueless.

 

I don't think the staining would cause any harm as long as the area passes the fingernail test. If you do pull the piston out to do rings, have some measurements taken of the bore and see if they are within spec. I would carefully remove the carbon ridge at the top (if anything is left after piston removal) and then take a clean oil soaked rag and wipe out the bore before reassembly.