Help with Datsun A12 Engine

[MadTkas]

Hi Ratsun Forum.
I recently got myself into the adventure of buying a 1982 Datsun B310 Sedan (with the A12 engine).
It always smoked a bit on startup, so I went into the adventure of changing the valve seals, but after I changed them it got worse and after leaving the car sitting for a few days, when I opened the engine it had a few mm of oil on top of the pistons (all 4 cylinders).
The engine had a lot of coke on the pistons, I believe it has been running rich for a good few years.
I done a compression check, and they are completely fine (all 4 cylinders were giving around 200).
I have a few questions though.

1 - Right now the head is being machined at the shop and getting new valve guides (should be done tomorrow), in terms of the pressure for the head bolts, some places recommend 40-43 ft-lb while others recommend 51-54 ft-lb so im a bit unsure what the best torque setting is.

2 - Is it common for the valve guides to be changed on this engine? (at the machine shop they said they change them quite frequently due to the fuel being more acid nowadays)

3 - When the car is hopefully back up and running, should I put any additive to help with the fact fuel doesnt have Lead nowadays?

Thank you

[datzenmike]

Mechanics always have some excuse for their customers as to why things are the way they are. If true, all old Datsuns would be blowing smoke and they don't.

 

Look on the tops of the head bolts. If stamped 12 then 40-43.

 

If stamped 13 then 51-54 You likely have these.

[Stoffregen Motorsports]

Yes, valve guides are a common replacement part. Replacing them takes minutes and is worth the extra cost. Ok, maybe takes half an hour if the head is all apart.

 

While you have the head off, hone the tops of the cylinders with a dingleberry hone (ball hone). This will give the rings a bit more life, even if it's just above the pistons. Obviously you want to do this with each piston down at the bottom of the bore.

[datzenmike]

22 hours ago, MadTkas said:

I done a compression check, and they are completely fine (all 4 cylinders were giving around 200).
 

 

If really 200 PSI I would leave alone.

[MadTkas]

I have just got the head back from the shop (they put the new types of guide seals and guides).
Now I just have to put it back together, I have a small issue though.
I got told that the bolts that have 12 (thats what I have) are meant to have 40 to 43 ft-lb, yet on "Gregorys Service and Repair Manual" they say 51 to 54 ft-lb.
What one should I go for?
The head it has is the version M30 052 (if it helps anything).
Thanks for all the help.

[Stoffregen Motorsports]

There were different grades of head bolts used over the years. I forget the markings on the bolt heads. Maybe a circle around the bolt head or maybe a stamped number?

[datzenmike]

On 2/23/2024 at 10:32 AM, MadTkas said:

I have just got the head back from the shop (they put the new types of guide seals and guides).
Now I just have to put it back together, I have a small issue though.
I got told that the bolts that have 12 (thats what I have) are meant to have 40 to 43 ft-lb, yet on "Gregorys Service and Repair Manual" they say 51 to 54 ft-lb.
What one should I go for?
The head it has is the version M30 052 (if it helps anything).
Thanks for all the help.

 

 

Asked and answered. Read your replies...

 

On 2/21/2024 at 3:16 PM, datzenmike said:

 

 

Look on the tops of the head bolts. If stamped 12 then 40-43.

 

If stamped 13 then 51-54 You likely have these.

 

[Stoffregen Motorsports]

Sorry Mike, even I missed that...

 

[Dguy210]

On 2/21/2024 at 2:54 PM, MadTkas said:

Hi Ratsun Forum.
I recently got myself into the adventure of buying a 1982 Datsun B310 Sedan (with the A12 engine).
It always smoked a bit on startup, so I went into the adventure of changing the valve seals, but after I changed them it got worse and after leaving the car sitting for a few days, when I opened the engine it had a few mm of oil on top of the pistons (all 4 cylinders).
The engine had a lot of coke on the pistons, I believe it has been running rich for a good few years.
I done a compression check, and they are completely fine (all 4 cylinders were giving around 200).
I have a few questions though.

1 - Right now the head is being machined at the shop and getting new valve guides (should be done tomorrow), in terms of the pressure for the head bolts, some places recommend 40-43 ft-lb while others recommend 51-54 ft-lb so im a bit unsure what the best torque setting is.

2 - Is it common for the valve guides to be changed on this engine? (at the machine shop they said they change them quite frequently due to the fuel being more acid nowadays)

3 - When the car is hopefully back up and running, should I put any additive to help with the fact fuel doesnt have Lead nowadays?

Thank you

 

 

Bad PCV valve can do that smoking too and would explain the compression being good and the valve seals not making a difference.

 

The A12A engine is the higher strength bolt heads marked 13, one bolt will be different and needs to go in the middle in the correct spot for oil flow. No lead additive is needed. But do add an oil additive for zinc (ZDDP). 

 

Note the A12 engine used in the 1200 and what most people refer to as an A12 has several distinct differences from the A12 engine in the B310. The A12 engine in the B310 should be thought of more as an A14 engine with smaller displacement than anything else. 

Edited February 25 by Dguy210

[Stoffregen Motorsports]

RIght. There are some differences across the years. I don't know if this is accurate, but I've always thought that the internal differences came when they moved the distributor back on the block and the alternator to the passenger side of the block.

Edited February 26 by Stoffregen Motorsports

[Dguy210]

11 hours ago, Stoffregen Motorsports said:

RIght. There are some differences across the years. I don't know if this is accurate, but I've always thought that the internal differences came when they moved the distributor back on the block and the alternator to the passenger side of the block.

That is my understanding of it also. Some other minor things of course but those are the big ones. From memory a little bit of difference in the block to head oil passages too.