Alfa Romeo Forum banner

1 - 19 of 19 Posts

·
Registered
Joined
·
1,659 Posts
Discussion Starter #1
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.




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



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




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.






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




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.




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.
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #2
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.




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...




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?






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.





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.




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



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.

 

·
Vendor
Joined
·
46,002 Posts
Cheers mate, interesting read. I've never done much with the old 12v, there are barely any left now. I've probably seen more of them in old Hawk Stratos replicas than I have in Alfas.
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #4
Cheers mate, interesting read. I've never done much with the old 12v, there are barely any left now. I've probably seen more of them in old Hawk Stratos replicas than I have in Alfas.

No probs, I'm having trouble finding bits and bobs for the 12v because of their rarity, which is why I thought it'd be a useful comparison to make - common wisdom says they're completely incompatible, but it looks like there's a lot of parts interchangeability apart from the heads / oil pump, and presumably the crank.

E.g people often say the sump from a 75 won't fit on a later 12v, but from what I can gather, excepting the oil pump issue, the main problem is the front panel with the crankshaft seal in it. But if the panel from a 12v will just bolt on, that's not such a problem after all :)
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #5
Quick update and more proof the internals are very similar - with the correct front cover the 12v crank fits fine:



As does the sump pan:





So the only issue would be the oil pump!
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #6
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



2.5 crankshaft



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:



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?
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #7
...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:



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:


And finally, some other goodies arrived today :D



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! :nono:
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #8
Final note before I get on with bolting the 12v bottom end together and sell the unused 24v bits - there wouldn't be any advantage swapping to the later cam tensioner on 12v / early 24v and in fact it might make it more likely to skip a cambelt tooth since the detensioners allow the engine to run a tighter cambelt on startup. But later cambelt tensioners are cheaper / easier to find so might be a good temporary swap whilst searching through hen's teeth for early tensioner parts.
Right, time to sell off all these 24v bits and get on with doing something useful :)
 

·
Registered
Joined
·
230 Posts
The 3.0 24V injector plates are 42mm ID. The bug QV runners are 45mm OD, same as the GTA runners. The 2.5 24V ones are smaller, maybe the same size as the 12V. That's why even on the Squadra tuning site it specifically mentions that anyone with a 156/166 2.5 24V who wants to install the 45mm QV runners need to get 3.0 injector plates. The runners are also smaller on the engine injector plate side, unless you get the 24V QV or GTA.

Not sure what size the GTV runners are, but the 164 Super 24V has small runners, but the injector plates are the same compared to the QV ones.

Maybe the engine you got had swapped injector plates and runners? Sometimes it's possible used engines get all the goodies swapped.
 
  • Like
Reactions: mj2k

·
Registered
Joined
·
120 Posts
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.
You'd probably get a few more horses but only at the top end. The 24v was tuned for a relatively flat torque curve to assist in low speed tractability. Narrower intake dimensions assist in low speed torque as airflow velocity is increased; of course at some point you restrict top end power. Increasing intake port diameter could actually reduce low speed torque.
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #11
You'd probably get a few more horses but only at the top end. The 24v was tuned for a relatively flat torque curve to assist in low speed tractability. Narrower intake dimensions assist in low speed torque as airflow velocity is increased; of course at some point you restrict top end power. Increasing intake port diameter could actually reduce low speed torque.
Interesting, and makes sense now I think about it, otherwise there'd be no need for twin plenums on some normally aspirated performance cars. It'd follow the same would apply to turbocharged cars too, smaller intake ports would assist low-end torque and at mid-range onwards the forced induction would take care of airflow, which explains why most road-going turbo cars have relatively restrictive inlet manifolds.
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #12
The 3.0 24V injector plates are 42mm ID. The bug QV runners are 45mm OD, same as the GTA runners. The 2.5 24V ones are smaller, maybe the same size as the 12V. That's why even on the Squadra tuning site it specifically mentions that anyone with a 156/166 2.5 24V who wants to install the 45mm QV runners need to get 3.0 injector plates. The runners are also smaller on the engine injector plate side, unless you get the 24V QV or GTA.

Not sure what size the GTV runners are, but the 164 Super 24V has small runners, but the injector plates are the same compared to the QV ones.

Maybe the engine you got had swapped injector plates and runners? Sometimes it's possible used engines get all the goodies swapped.

Sorry, didn't notice your post, yes it's entirely possible it already has all the 'goodies' - it was a part-finished project which was supposed to go in an Alfetta track car, but it looks like the project ground to a halt when the hybrid 75/164 oil pump proved to be an obstacle.
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #15
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.

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





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?
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #16
I got hold of an old (aka rather knackered internally) 75 / gtv6 engine with some nice ancillaries, so thought I'd do another set of comparisons between the 164 and the gtv6. Everything fitted just as you'd expect, but there was one interesting bit - 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





 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #17 (Edited)
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 (12v below):


You can plainly see the greater curve on the left hand side of the 24v's pump, which makes me wonder if the early 24v's waterway on that side has been redesigned too, and then returned to the original layout for the later 24v in the 916 gtv, 156, etc.

Many thanks to gussiegtv off Ebay for that pic :)
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #18 (Edited)
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)
  • Conrods will fit
  • Oil pump will fit if it's driveshaft is swapped
  • 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 with appropriate pulley swaps (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 mixture 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 there is virtually no parts commonality between Busso generations came from.
 

·
Registered
Joined
·
1,659 Posts
Discussion Starter #19
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.
 
1 - 19 of 19 Posts
Top