i bought myself a dead stock little 120y a couple of weeks ago to use as a cheap daily. it does have some rust but only on the panels and bottom of the doors none around the windows or in the sills. i just had the intention of bogging it up and painting over it to keep it nice and cheap but since then things have changed lol. i was out driving it one night and noticed that it was getting a bit hot so i stopped to check it out and saw that it was overheating due to a dodgy radiator. so i took the radiator out and replaced it with the one from my 1200 ute while the original one was being recored. i got the radiator back all fresh and new and was about to put it back in when i remembered that i had a spare reground cam sitting at home doing nothing so i decided to put it in, completely forgetting about the lifters and not realising how much work was really involved. so one thing lead to another and now im fully rebuilding my little A12. i would have gone for a bigger A15 but as i am on my ps that would require changine the engine number and getting it engineered and that would mean i couldnt drive it anyways. so im just gunna do a lot of internal work that cant be seen and as for the big webers 'sorry officer didnt they come like that?' haha
for starters i had an A15 oval port head at home that had been severly worked and ported and polished. so i took the head down to the local engine reconditioners and i was told that it had been shaved a huge 3mm which will be doing wonders for my compression. to complete the head im looking into some nice little parts from japan including double valve springs, retainers to suit, collets, and new valve guides which should make my head almost perfect for me.
as for the block i am having it bored out to 76mm to lift the capacity to about 1270cc. i will be getting some bigger pistons as well with a higher compression ratio hopefully lifting it to around 11:1 or about that. i will also be adding a heavy duty timing chain and adjustable tensioner from japan to handle it.
to finish the motor off i will be adding a couple of small 40mm webers and some 2" extractors. i will also be looking into a nice heavy duty clutch and 5 speed box or reconditioning my old 4 speed or maybe even a celica 5 speed depending on my funds. and then i can move onto the body work
i will add pictures of my progress and updates along the way. any help would be greatly appreciated from anyone

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Hi there,

Nice car, good to see another datto salvaged. Sorry to hear about the cam scenario, these little engines are fairly simple but they can get quite complicated if you don’t know your way around them. It’s probably a good thing you didn’t manage to get it in. If you install a fresh cam without freshly radius’d/faced tappets to suit you’ll wipe those lobes clean off with the old tappets. Well you run a very high risk of doing that.

First of all a few suggestions, you can save your self a whole lot of cash by simply shopping around, double valve springs can be sourced locally, personally I think the ones Crowe supply are the best for the money, try stay away from the ‘Competition’ brand ones, which are often advertised as competition double valve springs, making you think they’re for racing or something, they’re okay but for a little extra you can get the good-uns.

A 'severely worked head' isn’t the greatest thing, in fact it can have the opposite effect in a street car particularly if it has been heavily ported and had larger valves installed. I am running an ex-race engine in my car and although I have tamed down the head by using a stocker oval port, it is still an absolute dog to drive (but fun……ish).

As for milling, get the chambers cc’d and let us know what they are, I think each cc counts for half of a compression unit (let me confirm that) so yes, 3mm is pretty substantial across the chambers, but it just may make it. Beware, very high compression ratios will cause trouble, unless you have the access to high-octane performance fuels (and a wallet to match).

Stock retainers, stock spring seats, stock collets are all fine for a mild to hot street engine, so if you want to save some cash leave the bprojects bits for later on when you build an all out race motor. There are some small modifications you can do yourself to the retainers to lighten them and prep them (refer Datsun Competition manual in the wiki)

Boring out the engine 1.5mm should be okay but you’d need to find a good candidate, but coupling high comp pistons with the milled head would need some careful calculations before hand. The A-series engine is fairly robust in taking big bang comp ratios but be careful how you do it (no sharps edges, burrs or likely hot spots, chamber polishing to reduce carbon build-up and eliminate hot spots etc etc).

Heavy duty timing chain wouldn’t be necessary for a streeter but would be great on conscience (not that I’ve ever had a timing chain fail….ever) an OEM newbie would suffice.

Small 40mm webers? That’s about pushing it with the little A12/13 streeter. 40DCOE’s and some nice small chokes will keep the engine fairly economic and rsponsive(I use the term economic very loosely).

So there it is, just a little help. By the time you cut most of the unnecessary import performance gear out, you would almost certainly be able to afford a 5 speed.

But yeah work with what you got before you go the add-ons, do your calculations and double check your measurements and by all means don’t invest in the big-buck parts unless you’re building an absolute weapon of an engine, if you’re throwing all the good bits on an engine that doesn’t need them, you’re only spending more than you have to.

thanks for the help. as for the dual webers i was hoping to find a single manifold for it but i am yet to see one so i may as well use the twins.
also i was hoping i could get some advice on the cam regrind. the one i already have does not have any marking to say what it is so i am not really keen on using it but instead getting the stock one reground. and with the lifters would you recommend getting the stock ones machined or buying some new ones from jb racing? also with the bigger cam wouldnt i need double valve springs to increase the pressure to handle the bigger grind? and what if any modifications would i need to do to my pushrods?
i have not found out the head cc yet but hopefully i will know by this afternoon

Single manifold? There is one available on eBay, let me know if you want the link.

I'm running the Wade 224A which is a bit of a speedway preference, no good for road (I should say not ideal). The other that is getting good reports from Leigh AKA Lagwagon, Aidan AKA dat141 and a few others is the Wade 140, you need to double check that though that it’s suited to you. That's my next preference of camshaft when I pull this one out.

No need for JB lifters, if you want some broader faced lifters then I'm pretty sure some Navara ones interchange. Otherwise just machine the ones in there.

You don't NEED bigger valve springs, I'm running singles on my H75 and my GX has singles as well. They do increase performance but they’re only a necessity when high RPMS are involved.

Push rods do not need any work, maybe a polish to prep them a bit but that is about it.

All this lightened performance gear offered to the general public creates the impression that the stock parts are not adequate. The crux of the matter is that when you're wringing your A-Series over 8500rpm for extended periods of time, lightened tappets lightened push-rods and all that gear simply reduce the wear on your gear essentially letting you keep your engine that little bit longer. But for a street engine, the factory parts are quite tough and resilient.

Save you’re money on all the bling race gear and get the engine balanced, the flywheel lightened a nice heavy duty clutch and an oversize on the bores. Some cheap flat top pistons from an A10 could be used instead if you keep the stock bore.

In my opinion your best bang for buck is to buy and engine that has already had the work done to it. You never get your money back when you build them yourself.

yeah that single manifold link would be really helpful.
and what heavy duty clutch would you recommend and where from cause im finding it hard to get a hold of a decent one?
well im getting bige to help me with the pistons and gaskets and stuff so i should have no problems there

Ebay manifold looks to be round port. But its the cross flow type which is a good design. Speak to bige about it.

I'll send you the link.

i would have no hesitation in payin that amount for it but im looking for an A15 oval port single. if anyone has one that they dont want pm me!

block has just been sent away to get machined and bored out. and the rank has been sent to get done too.
so no one has a spare single A15 manifold???

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They do exist but are fairly uncommon. If memory serves me right, the US is the place to look for these "oval port singles"

yeah thank. well im thinking i should just get an A12 Single round port manifold and boring out or something to match up to my A15 oval port head. hopefully it can be done and works well