I am rebuilding a 1.3L engine and have both a G13A and a G13BA that I have disassembled. I plan to put together one good engine out of the parts. I have been told that the 2 engines are practically identical and all the parts can be interchanged ...BUT....there are some differences after all.

Both engines have the same size bore (74mm), but the G13A is 1324cc, while the G13BA is 1298cc. Since the bore is the same, the stroke must be different. And sure enough, the G13A has a slightly longer stroke. (I know, 'cause I measured and compared the 2 cranks).

It was easy to decide which crank to use in my new engine; the longer stroke yields more displacement. So, I had the G13A crank polished. I also had the block bored and the head surfaced, the valves ground and then I lapped the valves into the seats.

Then, while reassembling the head I noticed that the cams looked ALMOST identical. The only obvious difference is that one of the cams (don't know which is which at this point) is stamped "R1" and the other is stampede "R2". Figuring that there must be some kind of difference, I measured the lift (lobe height) and sure enough the "R2" has a slightly higher lift (taller lobe height). Thinking that more lift means better breathing, I assembled the head with the R2 cam. A little more thinking made me realize that I may have made a big mistake here.

Since replacement pistons are all the same for the G13A and the G13BA, I assume that the original pistons are the same also, which means that the pistons mounted on a G13A crank must come to TDC a little higher in the cylinder than the pistons mounted on a G13BA crank (G13BA crank has shorter stroke), unless the rods are different length. I didn't measure rod length because the pistons are still stuck in the G13BA block and I haven't bothered to remove them.

The problem is, I don't know whether the R1 or the R2 cam goes with the G13A or the G13BA, but I bet the higher lift cam goes with the shorter stroke crank, and vice versa.

Great, here I dun put a higher lift cam in the head and plan on bolting it to a block with a longer stroke crank! Sounds like a case where "piston meets valve, piston bends valve, idiot buys new valve".

I asked a couple of guys who work on these engines and they didn't know there was any difference between the cranks and cams on these engines. They said "oh, it'll be okay. Just run it".

I'm not so sure. Any ideas?

if the pistons are identical then the rods have to be different lengths. The easiest way to check things is to assemble and slowly turn the motor over by hand on an engine stand. If you use the wrong rods with the wrong pistons/crank you will either have a very low compression engine or an engine where the piston comes up the cyl. too far and hits the head!

Then, while reassembling the head I noticed that the cams looked ALMOST identical. The only obvious difference is that one of the cams (don't know which is which at this point) is stamped "R1" and the other is stampede "R2". Figuring that there must be some kind of difference, I measured the lift (lobe height) and sure enough the "R2" has a slightly higher lift (taller lobe height). Thinking that more lift means better breathing, I assembled the head with the R2 cam. A little more thinking made me realize that I may have made a big mistake here.

The ACL catalogue shows the 1298 and 1324 pistons as being different. The 1324 is dished with 'smaller' piston cutouts. The 1298 is flat topped with larger piston cutouts. It may be an error but the piston cutouts are shown as being in different locations. There are also subtle diffrences in dimensions. Actually it'll be easier to grab a pic than explain it.

OK heres the pic. The forum resizes images so you need to save it to your PC.



I think you need to start by comparing the pistons to see where the cutouts are and how deep they are from the top of the piston. Then turn over your engine and see if the pistons are flush with the block. If everything looks OK then put the higher lift cam in the head. Place some thick solder (2mm) in the piston cutout, hold it in place with a little gasket sealant. Then assemble the head, back the valve lash off a fair way. Then rotate the cam checking that there is no resistance. Gradually reduce the valve lash checking for clearance each time. If you get to the correct valve lash and everything seems OK then remove the head and check that the solder hasn't been squashed.  If it has and its less than around 1.5mm thick then you have a problem. Also note that this won't guarantee that you still have a non-interference engine.
You may find that the rocker arm ratios are different between the heads so it could all end up as stock.
I have a 1324 head in the garage but I can't see any markings on the cam, I could try and pull it but the screws are pretty mashed.

Great advice. Definitely a way to check it out before blindly tossing fate in the air. Thanks.

Regarding the piston specs, what do you suppose the "clearance and position" and "comp height" refer to?

Regarding the piston specs, what do you suppose the "clearance and position" and "comp height" refer to?

No idea, unfortunately I can't see it defined in the catalogue. If I remember I'll send them an email tonight One of the Antipodeans might know, IIRC CJ posted the original link to that catalogue

Compression hieght is the distance from the Center Line of the wrist pin to the top most part of the piston, (MOST OF THE TIME) some munfacures measure alittle different but that will get you close!

Piston clearance could mean about 50 deffernt things so I can't help there.

Compression hieght is the distance from the Center Line of the wrist pin to the top most part of the piston, (MOST OF THE TIME) some munfacures measure alittle different but that will get you close!

That would have been my guess. Is that the height to the outside edge of the piston. (ie the bit that always flat) and not inclufing any dome or dish in the centre. I hope you can understand that.