Hello Datsun1200 members....1st post but very familiar with the site. I have come to the conclusion to transform my 72 MG Midget into a Japanese/British hybrid car. The A series engine is an excellent choice as suggested by many MG owners. I was directed to this site for expertise in rebuilding and identifying parts as I accumulate them. By reading numerous threads, I have definitely come to the right place and hope I get the help I need as I move along. My intentions are no more than 80-90 HP and a mild rebuild with twin carbs I picked up from an A12 motor. First order of business is fabricating motor mounts and other modifications to the chassis but want to get some engine information as the chassis work gets done so that it can go to a machine shop afterwards.

I have acquired an A15 engine from a 1982 B310 car (pic attached) which had about 200K miles and surprisingly the motor turned freely and the cylinders appear to be real good shape. Even the timing gears look to be in good condition. The H95 head will sit on the shelf and be replaced with a GX head (I think) from another purchase. Reading the 1200 tech data, it does appear to be the GX head. No numbers are stamped on top, only Japan Nissan. Also have the intake and exhaust manifold. This all came from a 1972 Coupe. My concern is that the engine does not have a dual point distributor. Is it a GX head?

My understanding is that the A series cylinder heads are interchangeable with the different blocks. I read on one of the threads that an oil passage hole has to be drilled if a GX head is used with the A15 block. Any information on this would be appreciated as well as camshaft modification and other rebuild advice. Can I use the lifters that were used with the H95 head? Enough said for now and will wait for replies and post more pictures later. Thanks.

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Hi TexasMidget, welcome to the club.

GX engine has special distributor, but it is not dual-points. It had a slower mechanical advance, so it is not very desirable. The A15 (USA) distributor is far superior since it is a high-energy electronic ignition type. Of course with any engine buildup you will want to recurve the distributor for maximum power.

If you use an A15 head on a GX block the oil passage needs to be drilled. But with newer engines like the A15 no mods are needed. See Head Interchanging.

Yes, that appears to be a GX head:
* Extra-large oval ports about 36 mm tall with large water ports below
* Has an oil hole between cylinder2 and cylinder 3 pushrod holes

* The GX setup (head, carbs & exhaust and camshaft) was good for 83 HP

* The 1981-1982 A15 was only good for about 75 HP , due to small oval ports & small camshaft (5600 RPM).

So to get 83 HP (at the engine, where all car manufacturers measure Horsepower), you will need:
* GX head, carbs, exhaust
* GX camshaft (6400 rpm)
* 1.75" exhaust (stock GX used 1.5" exhaust so don't overdo it)
* To rev the engine to 6400 RPM. It will make less HP at lower RPMs.

An A15 grind of the GX cam is Nissan part number 13001-H5700. But any camshaft company can make a cam to spec. Tell them you want a grind for max HP at 6400 rpm. Iskenderian is suggested as they have Datsun experience - call them by phone to request a custom grind (you won't find it in their catalog). You will also need the Nissan dual valve springs. Avoid if possible, aftermarket dual valve springs since they will reduce HP (they are very stiff for 9000 RPM use, you only need 6400 RPM springs). The stock A15 springs are good for 6000 RPM and start to float around 6400 RPM.

All A-series engine use the same lifters, but the lifters should not be reused. Use only new or re-faced lifters whenever you change the cam. Use cam lube and follow the cam manufacturer's break-in procedure.

By the way, the A12GX cam won't work in newer 1974-up engines as the oil-pump gear drive was moved.

Flat-top pistons were used on the GX, however they are not needed on the A15 (they gain about 2 hp, but are about $400/set).

average 2 door sunny sedans are worth mint Yen in Japan

Thanks DDgonzal! I have 10 more questions (for now....... :

1. If cylinder bore is ok, can I reuse pistons and simply hone and replace rings? No need to replace pistons with this size dish that is matched up with GX head?
2. Turn crankshaft and replace bearings. I have some end play, which will need to be repaired?
3. Replace camshaft and lifters as you noted. Install new cam bearings. Can I reuse the pushrods from the A15 cylinder head?
4. Do I replace freeze plugs?
5. http://datsun1200.com/modules/mediawi ... shaft_replacement....This link indicates more than 15mm extension of the tensioner replace the timing chain. If so, can I reuse the gears or replace both gears as well?
6. Replace oil pump?
7. Expect to replace all GX head valve springs?
8. Will plan to get the cylinder head rebuilt. Any advice here? History of A12 engine is unknown.
9. Will the GX exhaust manifold work that I show in the pictures? Is this the stock GX exhaust? I couldnt believe what someone was asking for this in the classified section.
10. Carbs will need to be rebuilt. Any additional information on these based on what you see in the pictures?

Any response would be greatly appreciated. I am sure I will have many more questions later on. I did have an opportunity to talk with Peter Zekert and he advised not to bother with dipping the block in any harsh chemicals when it goes to a machine shop and not to replace any freeze plugs. The A series blocks have longevity and dont require much if your wanting only a mild rebuild. Let me know what you think about that.

BTW, history on the 72 coupe is that the previous owner bought the car for the body only and put a 240sx motor in it and was parting with the A12 engine and transmission. Unfortunately its the 4 speed. I have read where the 5 speed GX transmission is very rare.

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1. If cylinder bore is ok, can I reuse pistons and simply hone and replace rings? No need to replace pistons with this size dish that is matched up with GX head?

Yes. CC the pistons and the head to determine the compression ratio. Up to 11:1 is OK for premium gasoline.

2. Turn crankshaft and replace bearings. I have some end play, which will need to be repaired?

End play needs to be fixed. Turning the crank is rarely needed unless the crank is damaged.

3. Replace camshaft and lifters as you noted. Install new cam bearings. Can I reuse the pushrods from the A15 cylinder head?

Negatory on the cam bearings. They last the life of the engine. If you do replace them it requires machining.

Yes, reuse the pushrods.

4. Do I replace freeze plugs?

Only if they are damaged, pitted or soft. It's hard to tell so most replace them regardless.

5. camshaft_replacement....This link indicates more than 15mm extension of the tensioner replace the timing chain. If so, can I reuse the gears or replace both gears as well?

From your photo, you have less than 10mm extended. But if more than 15, swap the A12 gears and chain onto the A15. It's the same. The factory Datsun double-roller chain is super strong and virtually never wears out.

6. Replace oil pump?

Not usually. Not unless it is visibly worn. Disassemble and view the insides. If it doesn't look worn, reuse it. If you see any wear or scoring, then replace it.

7. Expect to replace all GX head valve springs?

Depends. Inspect them per the factory service manual for length and pressure. 40 year old springs are still turning to redline.

8. Will plan to get the cylinder head rebuilt. Any advice here? History of A12 engine is unknown.

Not usually needed. Inspect the head per inpecting a used head

9. Will the GX exhaust manifold work that I show in the pictures? Is this the stock GX exhaust? I couldnt believe what someone was asking for this in the classified section.

Yes it's worth $600. And better than a tubular header for general all around street use.

10. Carbs will need to be rebuilt. Any additional information on these based on what you see in the pictures?

Su-type carbs are super-simple. Only need rebuilding if the shafts are no longer tight. Otherwise "rebuilding" means cleaning and adjusting. See Twin Carb adjustment. If your goal is to make them look new, Z-Therapy can do it. Otherwise just use them and enjoy them.

Yes, 5-speed is very rare. And not strong enough to use with an A15, so use an A14/A15 heavy duty transmission.

Much thanks ddgonzal! The following is a continuation of the previous questions....

1. Is there a link on this forum for measuring CC?
2. Replace crankshaft main bearings? Do the piston rods have bearings and replace them as well?
3. OK
4. OK
5. Measured 11mm. So go ahead with swapping out the A12 gears and chain? Should I replace the tensioner?
6. OK
7. http://datsun1200.com/modules/mediawi ... ?title=Valve_springs...is this the link for checking the springs?
8. OK. I would expect to replace valve guides but will use the method described on the link. I did use a straight edge and couldnt see any gaps. It looked real flat. Will get a more accurate straight edge and use the feeler gauge test. Does the rocker assembly require anything?
9. OK
10. OK

Do I take the engine block to a machine shop and have them dip it into a solvent tank to clean the inside? Will that harm the cam bearings?


Also........I have been rummaging salvage yards in the North Texas area and came across a cylinder head from a 1974 B210 car (80 HP engine). I know about the H72 head but this one has 4 digits H7240. Does this mean anything? My intentions are to accumulate hard to get Datsun parts that are worthy in the event I want to take on another project. There aren't many Datsun cars left.

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1. Is there a link on this forum for measuring CC?

CCing

2. Replace crankshaft main bearings? Do the piston rods have bearings and replace them as well?

Inspect. Replace if scored or worn out of spec. Usually they last over 200,000 miles. See Bearings


5. Measured 11mm. So go ahead with swapping out the A12 gears and chain? Should I replace the tensioner?

No need to replace. It's well within the 15mm service limit.


7. Valve_springs...is this the link for checking the springs?

We have no link, the process and specs are in the factory service manual.


8. OK. I would expect to replace valve guides but will use the method described on the link. I did use a straight edge and couldnt see any gaps. It looked real flat. Will get a more accurate straight edge and use the feeler gauge test. Does the rocker assembly require anything?

No. As long as the rockers pivot freely it's OK. If they bind, replace the shaft.


> Do I take the engine block to a machine shop and have them dip it into a solvent tank to clean the inside? Will that harm the cam bearings?

Yes, generally hot-tanking will damage the bearings. Unless the block is unusally dirty, don't have it dip-tanked.


> I know about the H72 head but this one has 4 digits H7240. Does this mean anything?

H72 casting is machined in various version. For USA, it machined for anti-pollution gear with air passage drilled through the exhaust ports. OK head but prone to pinging.

1974: 1.3 liter engine, 75 HP smaller oval port cylinder head
1975: 1.4 liter engine, 80 HP oval port cylinder head
Some H72 are round-port heads (65 hp).

Unknown which one the H7240 is. You can measure the intake port dimensions and let us know.

I should say that I don't have the specs for the GX valve springs. The testing process is listed at Valve springs, but it only shows the regular spring specs.

I tried to translate the Japan factory service manual (Page 123) for the dual-spring specifications.

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