Comparing Busso internals - 75 12v vs 916 GTA 24v

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mj2k
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Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

Another day, another speculative Ebay purchase. I found a cheap 916 gtv Busso block on Ebay, minus it's sump, conrods, crankshaft, liners, etc. The chrome trumpets looked in pretty good condition (except for one small dent) and I thought I could do a quick comparison between the 12v and 24v blocks before I binned the rest, so thought 'why not'?

When I went to pick them up it turns out the block isn't the sad remains of catastrophic bottom end failure, it's actually a near-immaculate low mileage block which has been used for speccing and measuring by an engineering shop who supplied parts for EBSpares :D

So if anyone needs a very nice 24v 3.0 block or heads, drop me a PM :)

But without further ado, down to the comparison...

Firstly, the really, really interesting bit. Looking at the casting for the 24v pump vs the 12v pump, you can see there are small differences in the cavity size, but the waterways and bolt holes match perfectly.

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And sure enough, a 12v pump fits into the space rather nicely, and spins freely when bolted down.

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Following through, I could see no discernible difference between the 12v and 24v heads' or blocks' waterways.

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And even more interesting, it looks like it'd be a simple job to remove the core plugs from the front of the 24v heads and block off the waterway at the rear end, to make it suitable for a front-mounted stat.

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Rest of block is extremely similar (24v would have an extra bit bolted on to hold the oil filter, though presumably the housing could easily be tapped to accept the older type oil filter if necessary). So, could it be, after all these years of commonly held wisdom, that the more modern 24v can easily be converted to have it's stat and housing at the cambelt side of the engine?

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However, there is one fly in the ointment - spot the difference:

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Damn. Though the bracket at the bottom could easily be modified to take an early 164 24v's pump, the casting the pump shaft would need to run through has been removed.

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The common way around this is either to modify a 75 sump to fit around the later 916-style oil pump, or to dry sump it. And I don't have the skill / expertise to do either of those, so sadly, despite it's lovely condition, this block's no use to me. I won't have any use for the 24v heads either, since they're lacking the necessary casting too.

However, it looks like all the bolt holes for fitting a hydraulic detensioner are still present, though I've no idea if it'd be possible to drill though to an oil gallery to supply the necessary pressure for it since the casting in that area has changed.

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Unless I've missed something or someone's tried similar experiments in the past and come a cropper, that opens up something really interesting for 116 GTV and 75 owners - theoretically you can easily convert a later-type engine so it won't foul the bulkhead. This means you could fit a 3.2 'GTA' type engine with minimal modification to the cooling system and none to the bulkhead at all! You would need to do some engineering around the oil pump issue, though that'd be no problem at all for a race engine since presumably it'd be dry sumped anyway.

One other interesting difference - the 24v block has extra drillings in the main bearings leading to spray jets mounted beneath the pistons, whereas the 12v doesn't. Wish I could reverse engineer that bit...

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Ok, on to other comparisons.

Unsurprisingly the inlet and exhaust ports for the 12v and 24v are completely different. 1-0 to the later 24v. Or is it?

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As are the inlets. But the injectors look the same, so I'm keeping those.
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12v and 24v plenums are exactly the same size, apart from the mounting and 'bling' the only difference is the later 24v has a different mounting flange for the throttle body.

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And now for the interesting bit in this; good for me, not so good for 24v owners. The 24v trumpet size exactly matches the 12v inlet, there is no step whatsoever.

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And also the 12v 164 inlet has exactly the same bore as the old 116 2.5 GTV inlet too.

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So that means the 3.0 24v which should theoretically be able to suck in much more air through it's extra valves and increased displacement, can only breathe as well as the venerable 2.5 12v! Bet a few horses could be easily released from a later 24v simply by fitting it with a bigger plenum and trumpets which actually fit...
Finally, the common bits. Everything from the front end of a 12v will just bolt on to a later 24v; that came as a surprise too.

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LooLooSud33Spider
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by LooLooSud33Spider »

Alternatively Marc you could always go dry sump . It isn’t too hard to convert and it would solve all your sump and pump problems .
Lou
Alfasud Ti 1984
Alfa Spider 2.0 Ts 916
Alfa Spider 20v Turbo

mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

LooLooSud33Spider wrote:Alternatively Marc you could always go dry sump . It isn’t too hard to convert and it would solve all your sump and pump problems .
Lou
I was thinking about that, but for a road car it wouldn't really be practical; there wouldn't be enough room for the oil reservoir in the engine compartment and you wouldn't want it in the passenger compartment, so it would have to go in the boot, which could be a recipe for disaster if you didn't carefully keep an eye on it (which I wouldn't do if I was using it as a daily driver).

Wonder if there'd be any way to do a 'moist sump' so to speak, and use a dry sump pump but keep the oil reservoir in the sump pan? Hmmm....

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LooLooSud33Spider
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by LooLooSud33Spider »

That is certainly a possibility Marc all you’d effectively be doing is replacing the internal pump with an externally mounted one. The Alfa Montreal had a similar system. It had a wet sump but also a had a separate external oil tank. I have a diagram of the Monty oil system That I’ll try to post so you can have a butchers. It May give you some ideas.
Alfasud Ti 1984
Alfa Spider 2.0 Ts 916
Alfa Spider 20v Turbo

mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

Thanks Lou, could be interesting to see :)

I reckon just fitting an extractor at the lowest part of the sump followed by a remote filter, cooler and single stage external pump feeding back through the normal oil filter fitting would do it, but even the cheapest external single stage pump is about £500 (unless you buy a random Chinese clone) so not a cheap option...

mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

Quick update and more proof the internals are very similar - with the correct front cover the 12v crank fits fine:

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As does the sump pan:

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So the only issue would be the oil pump!

However this has all become a bit irrelevant for me since I've just discovered the 'cavitation' on my 12v block is present on the near-new 24v block too, and since it doesn't seem to do anything, the weird holes must just be from casting. So assuming my forged 12v pistons turn up, no reason to go down the 24v route :)

mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

And the final one in the series - 2.5 24v crankshaft with 3.0 pistons and rods. Should be no issue at all since the conrods are the same length and sure enough, it isn't

3.0 crankshaft
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2.5 crankshaft
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So using the 2.5 crankshaft would give a low compression engine (roughly 7.0:1) ideal for turbocharging, and would have the advantage of making it a non-interference engine so less chance of catastrophic damage if the cambelt snaps :D

Don't think this 2.5 crankshaft would be much good as it is however - there is one vital difference between the 12v 3.0 crankshaft and the 2.5 24v - the bearing which the oil seal beds down on is missing from the later one:
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The space where it should be is normally filled by the oil pump drive cog. Anyone got one of those going spare which I can grind down by any chance?

mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

...And another little update, I saw a front crankcase cover brand new on Ebay for £20 for the later 24v, so thought I might as well get it so I could compare the old vs new covers, and this well and truly explains where the idea the 116-style sump won't fit on a 24v without drilling new bolt holes comes from:

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You can plainly see the bolt holes are in different places, but the rest of the crankcase bolt holes line up just fine with the sump. So to fit a 116-style sump to a late 24v or vice versa, you just need the front cover (excluding the oil pump issues noted above).

And also interestingly putting the new front cover on the old 12v crankcase clearly illustrates how the more modern solid cambelt tensioner is fitted - it does just bolt in place of where the hydraulic detensioner was fitted, just with a longer extension on the front cover to firmly hold it in place:
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And finally, some other goodies arrived today :D

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They won't be used quite yet (need to make sure the engine runs reliably as it is first) but the pistons are dramatically different to the originals, all are within 1g of each other, and they're considerably lighter too. But somewhat bizarrely, the gudgeon pins are also only within 1g of each other, and there's one more 'heavy' gudgeon pin than 'light' piston so might have to get one pin machined a little to make them balance perfectly.

Must... Resist... Using... Them!

Kegsti66
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by Kegsti66 »

This thread is really interesting and I am sure very helpful to many people.
You have really looked into some useful issues here, thanks for sharing.
Great stuff, and good luck with the build.

mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

I managed to crock myself a month and a bit ago stupidly trying to lift a transaxle out of my car without an engine hoist (did some damage internally somehow, not a bad back!) so I haven't been able to do anything with the engine proper, but I have sold most of the 3.0 24v bits now, except the cam covers.

But I picked up an original 116 GTV 2.5 v6 crankshaft for a song including postage, so thought I'd share the comparison between the 2.5 v6 24v crankshaft and the original 'long' 2.5 12v shaft.

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Suffice to say never the twain shall meet! Creating an extra shim for the flywheel and creating an extra bearing for the front cover (in place of the 24v's oil pump drive) would be a ridiculous amount of work and would probably result in a heavier, weaker crankshaft with some seepage from the front cover, so as effectively non-interchangeable as the block and heads.

Which also raises the question - since creating a shim to fit the earlier 'long shaft' flywheel to a later engine would put the shim further away from the bearing (this increasing the mechanical force and risk of the shaft being out of balance) than the original crankshaft (which effectively has the shim cast right next to the rear bearing), would this mean using the earlier type flywheel with the later type crankshaft could possibly lessen engine life a little?

mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

Time for more comparisons...

I picked up a 2.5 12v engine which is either from a gtv6 or a 75 2.5; by the looks of the serial number and long crankshaft the former is more likely, though it does have loosely bolted on 75 ancillaries which I plan to transfer to my 3.0 12v project.

Pulley bolt came off incredibly easily - knocked out the staking and hit it with an impact wrench and off it came!

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Also took off the pipework on top of the thermostat housing; you can clearly see here the difference between the 'stat housing on the 164 and 75:

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Pipe outlets are on opposite sides

And then stripped off the inlets / fuel injector rail (which look identical to the gtv6 ones I've got already):

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Then finally stripped off the flywheel cover, battery earth strap and flywheel:

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Flywheel is the old gtv6 style and it's a 'long' crankshaft, which is a little disappointing; I was hoping it was the modified 75 ype so I could put it straight on the 3.0 block. Oh well.

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Further stripping down revealed it's in pretty poor condition internally, surprising given the plugs were left in and it was regularly rotated / treated with WD40, which is yet further evidence this is most likely a gtv engine which has been sitting for a long time:

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So the engine's not as useful as I hoped - it's in need of a rebuild and the flywheel isn't really much use if I stick to the 3.0 shaft.

Next steps will be to do some more comparisons between the 3.0 and 2.5 v6 blocks, etc (I suspect there won't be many differences to note), followed by a trial fitting of the better of the two 2.5 crankshafts.

Once that's done I'll either break the remains of the 2.5 engine for spares, or reassemble it and sell it on cheap as needing a rebuild once I've claimed the bits I want off it. Give me a shout if you either fancy a 2.5 in need of a little TLC for around £150ish or need parts from it (e.g the heads which look good, the crankshaft which looks OKish, good looking block with rusty liners, etc) since that'll help me to make up my mind what to do with the block.

Edit: Oh, and here's another interesting little factlet - the early 3.0 24v from the 164 has a different water pump housing to the 12v to stop it fouling the oil pump drive pulley on the earlier 24v heads. And since the cambet tensioner is a drastically different design I suspect a 12v tensioner won't bolt on to an early 24v block either. Which suggests there's less parts interchangeability between the early 24v and the late 24v than there is between the late 24v and the 12v....

And here's the proof of the difference between the 12v pump and early 24v pump:
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Many thanks to gussiegtv off Ebay for that pic :)
Last edited by mj2k on Fri Sep 06, 2019 12:33 am, edited 2 times in total.

mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

Well, that was more interesting than I thought - the 2.5 'long' crankshaft fits straight into the 3.0 12v block with no adaptations wahtsoever, even the bearing caps fit straight off!

And the 2.5 gtv flywheel fits straight on, as does either the gtv, 75 or 164 crank pulley

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mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

So in summary...

164 3.0 12v -> 75 3.0 12v (and vice versa)
Almost everything will swap over, including the pump / distributor / sump with no issues as long as you have a donor engine with the correct flywheel, ancillaries, etc

Alfetta (or 75?) 2.5 12v -> 164 3.0 12v (and vice versa)
Ditto. But you'd need to swap the crankshaft (giving you a low compression 2.8) or create a 4mm spacer and get the flywheel balanced with the 3.0 crankshaft / pulley to avoid the engine becoming unbalanced if you used a 2.5 flywheel, and you would need to fiddle with the starter mounts to ensure it lines up correctly.
Pistons / heads of course won't swap over because the engines have a different bore, but conrods are fine

75 / 164 3.0 12v -> later type 3.0 24v (from 916 GTV, 166, etc)
Pistons won't swap (different cutouts) but conrods will.
Heads won't swap without work (you'd end up with a big hole in the left hand head where the oil pump drive went, which would need closing up)
Crankshaft / sump will swap, but you'd need to fit the appropriate front cover and you'd need to create some alternative oil pump drive / pickup using a dry sump pump.
Water pump / waterways should fit with a little adjustment (see above posts)
Timing belt detensioner won't fit - it'd need a feed from an oilway, which probably isn't routed in the same place on the later 24v block
Ancillaries might need new mounting holes drilling but should work with the correct front pulley

Later type 3.0 24v (from 916 GTV, 166, etc) -> 75 / 164 3.0 12v
Pistons won't swap (different cutouts) but conrods will.
Heads won't swap without a lot of work - you'd end up with a big hole in the crankshaft where the oil pump drive went, which would need closing up, and you'd need to create some alternative oil pump drive / pickup using a dry sump pump.
Crankshaft / sump will swap, but you'd need to fit the appropriate front cover and you'd need to create some alternative oil pump drive / pickup using a dry sump pump. Also you'd need to knock off the oil pump drive cog and create a shim / spacer to replace it
Water pump / waterways should fit with a little adjustment (see above posts)
Timing belt tensioner will fit, just a matter of blocking off the 12v tensioner's oil feed
Ancillaries might need new mounting holes drilling but should work with the correct front pulley

164 3.0 12v -> 164 3.0 24v (and vice versa)
Ancillaries might fit (unknown)
Oil pump will fit if it's driveshaft is swapped
Conrods will fit
Almost no other parts in common, and block is sufficiently different to make parts swapping tricky

164 3.0 24v-> later type 3.0 24v (and vice versa)
Conrods will fit. Pistons might fit (unknown)
Ancillaries might fit (unknown)
Almost no other parts in common, and block is sufficiently different to make parts swapping tricky

Alfetta (or 75?) 2.5 12v -> later type 2.5 24v (from 156, 166, etc) and all other combinations
Not tried, but presumably will be a misture of 2.5 12v -> 3.0 24v and 2.5 12v -> 3.0 12v, etc. Doubt it'd be worth all the work though...

Weird how the early 3.0 24v is so different to the rest, maybe that's where the commonly held view that nothing will fit came from.

mj2k
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Re: Comparing Busso internals - 75 12v vs 916 GTA 24v

Post by mj2k »

I've given the 2.5 block a quick cleanup and lightly glaze busted the bores to see how bad the rust really was, and it's not too bad over all. I haven't checked the rods for straightness or crankshaft for ovality, but it turns nice and freely now the surface rust is out of the way.

Realistically the bores will need honing to get rid of the rust residue (it may be cheaper to replace the liners though, depending on what bargains you find on t'internet) and it'd be silly not to replace the bearings and polish the crankshaft while you're at it, but it looks perfectly useable so I've stuck it on Ebay:

https://www.ebay.co.uk/itm/293222519210

Drop me a personal message if you fancy it, and I'll knock another 20% off if we arrange collection through here.

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