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Discussion Starter · #21 ·
Can I just check.... looking at the photo / image you posted 3 weeks ago with the 2 pistons sectioned through, is a 16v piston dished - as shown in the image? I thought from memory they were flat across the top?? :confused:
 

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Discussion Starter · #22 ·
http://i.ebayimg.com/00/s/MTIwMFgxNjAw/z/5Q8AAOSwxYxUwumX/$_57.JPG

Ah, no... I can see now that there is as you say a slight dish. Not the best image (from eBay) but with the sellers other images you can in fact see that the top of a §6v piston is dished. Silly me!

(sorry - you would have to copy and paste the image address into your search bar if you wanted to view it - its from eBay so doesn't copy exactly as a clickable link)
 

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Yes the 16v piston is dished, just not as much as the 8v, like the picture suggests :)
I'm doing the same calculations as i have a project motor 8v to be bored to 89mm to accept Nissan pistons (from for example 240SX) that are in all other ways compatible but have 1mm lower compression height (distance piston pin to top of piston) and I will be using reworked 1.5 105HP heads that have the same valves as the 1700 8v heads but are almost flat where the 1700 heads have a compression chamber, it's like the same puzzle as yours and in the end I think I will have to do the measuring with paraffin.
 

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Discussion Starter · #24 ·
Yes - on my other project engine I have 89mm bores but with high compression roughly 12:1 CR pistons.

They certainly weren't cheap! I have bought fully working cars that are cheaper.

Will stick a photo up in a while.
 

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Hi Ed

This may help.

I've made a note that the id of a 16V gasket is 88.15mm. Compressed gasket thickness I have as being 1.4mm at 65lbs/ft
Cylinder head capacity is 28.8cc
With these figures you should be able to back calc the capacity of a 16V piston

On my rallycar engine we had pistons out of block by 0.37mm
I reckon on a std bore for every 0.1mm the piston is above / below the block the CR will change by 0.11. Standard CR is 10.1:1


rsfruitbat
 

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Yes the 16v piston is dished, just not as much as the 8v, like the picture suggests :)
I'm doing the same calculations as i have a project motor 8v to be bored to 89mm to accept Nissan pistons (from for example 240SX) that are in all other ways compatible but have 1mm lower compression height (distance piston pin to top of piston) and I will be using reworked 1.5 105HP heads that have the same valves as the 1700 8v heads but are almost flat where the 1700 heads have a compression chamber, it's like the same puzzle as yours and in the end I think I will have to do the measuring with paraffin.
Hi, this post is very interesting.
So you mean 105HP heads with 40mm in-valve and with almost flat (little) chamber.

Are you searching for heads from older boxer with mechanical tappets
or could be usable also the more easy to find heads from 1350-1490cc
1990-94 (hydraulical tappets)?
They also have 40mm valve and I think quite flat chamber,
non sure if less or equally flat respect to older 105HP motor
with mechanical tappets, some-one have compared them?

Also the 1490cc twin carb hydraulic tappets 1990-92 have 105HP
but I think with more all-around camshafts than old mechanical tappets 105Hp
(in 1990-94 camshaft and 40mm-33mm valves are the same for 1.3-1.5-1.7 8v).
 

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The heads from the 1.5 105hp Sud TI QV/early 33 QV have mechanical tappets with shims and a pair of those I will be using. They have 40mm inlet valves but the channels are normally for 36mm carbs. My heads came with a lot of other parts and they have inlet channels 40mm. Not sure if there was a factory 1.5 with 40mm carbs or if this was done by a previous owner. I prefer mechanical tappets instead of hydraulic and besides, I have a pair of C&B fast road cams for mechanical tappets. In the first pic, compare 1.5 105hp head with 1700QV/IE head. Second pic the inlet channels, look how smooth the 1.5 105hp channels are compared to the 1700.
 

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Discussion Starter · #28 ·
https://fbcdn-sphotos-g-a.akamaihd...._=1435331483_5b4913fe55811367e39470d4fd4da6ed

I thought this was a really interesting image.

You can see the shape of the 16v chamber - what is interesting for me is noticing how close to the edge of the chamber the valve starts from. It seems that the valve starts from almost the very edge of the chamber. I am just trying to think (in a not very scientific way) just how much more volume there is in an 16v head - compared to a 8v head. May need to take some volume measurements.
 

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Discussion Starter · #29 ·
Thanks for that RS Fruitbat,


Looks like I may have to get my calculator out.....:)

Does anyone happen to know the cylinder head volume of an 8v cylinder chamber, just out of interest?

Hi Ed

This may help.

I've made a note that the id of a 16V gasket is 88.15mm. Compressed gasket thickness I have as being 1.4mm at 65lbs/ft
Cylinder head capacity is 28.8cc
With these figures you should be able to back calc the capacity of a 16V piston

On my rallycar engine we had pistons out of block by 0.37mm
I reckon on a std bore for every 0.1mm the piston is above / below the block the CR will change by 0.11. Standard CR is 10.1:1


rsfruitbat
 

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I also will search on forums for the volumes of 8v chamber..

Ps.: I have seen last photos from Bert and I was wrong,
the heads for 1.3/1.5 of years 1990-94 (hydraulic tappets)
are not "quite flat", they seams exactly same chamber form
as the 1,7 8v head in the last photos..I also put two photos

I'm a bit interested to know which are the differences
between 1.7 heads (1988-1994) and 1.3-1.5 heads (1990-94),
if are important (for ex. like different in-out channels) or minimal..

I know heads for 1.7 are specific (they have one
different alfa spare code respect 1.3-1.5 1990-1994)
so some details must be different, I was thinking it
was a different chamber, but now I really don't know?

Apparently 1.7 heads have same specification of 1.3-1.5 heads:
- similar (identical?) chamber (see photo attached)
- same 40-33 valves (same alfa spare code)
- same camshaft (same alfa spare code)
- same (hydraulic) tappets (same alfa spare code)
- same water/oil passages disposition/diameter
- same inlet channel diameter (see photo attached,
about 37mm diameter at (upper) surface, but 33mm
effective diameter some mm below surface
)

- may be have different diameter out-passages?
For 1.3/1.5 out-channel are 30mm diameter
measured at the head (under) surface,
may be in 1.7 heads are bigger?

An so, if chambers are similar, to fit higher 72mm stroke,
pistons of 1.7 8v must be 2mm lower than 1.3-1.5 pistons?
 

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Capacity in std 16v piston is 9.7cc. Just found a note.

From memory the 8V head dish was very small maybe 8cc. A little bit of skimming and it was gone.

rsfruitbat
 

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Discussion Starter · #32 ·
Well .... here is the latest plan.

I have sent off a 16v piston - and asked the engine builder to cut the rim of the 8v piston to match the cut out positions of the 16v piston top. I can't imagine there will be a great deal of cutting to do, as very quickly the cut out will disappear in the deeper well in the top of the 8 valve piston. Anyway, that is the plan at the moment. Let's see what he comes back with.....
 

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Discussion Starter · #33 ·
does anyone know....

deep in the head - below the 2 springs there is a flat metal base plate with a rim on it, that the 2 springs sit on. It seems that there is also a flat washer sat in that base plate. Does anyone know for sure - is it a flat washer in each and every valve pocket, or just the inlet or exhaust, or some random pattern?
 

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Discussion Starter · #34 ·
Ok.... so recent progress.

I took the 8v pistons to the engine builders and had them cut to represent the 16v pistons - if that makes sense.

Here is an 8v piston that has been machined to take a 16v valve configuration. Was unbelievably expensive to have this done - but considerably cheaper than buying completely new pistons. Any thoughts......

http://i997.photobucket.com/albums/af95/edwardgurhy1/IMG_1877_zps0oebnkbr.jpg
http://i997.photobucket.com/albums/af95/edwardgurhy1/IMG_1878_zpsikvox4cq.jpg
 

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Ok.... so recent progress.

I took the 8v pistons to the engine builders and had them cut to represent the 16v pistons - if that makes sense.

Here is an 8v piston that has been machined to take a 16v valve configuration. Was unbelievably expensive to have this done - but considerably cheaper than buying completely new pistons. Any thoughts......

http://i997.photobucket.com/albums/af95/edwardgurhy1/IMG_1877_zps0oebnkbr.jpg
http://i997.photobucket.com/albums/af95/edwardgurhy1/IMG_1878_zpsikvox4cq.jpg
Hi, very neat work!
it is my impression or you have request a very deep space for valves,
visibly more deep than standard 16v pistons? 2 mm more deep?
are you planning to use big cams or because you'll have to skim the heads?

Ps.: after you say it was an expensive work I was trying to imagine
how similar work could be done DYS using non professional tools,
like a mill on a vertical drill used on pistons blocked on angled support,
but it would require some time to build the support and probably
the work wouldn't end with the same neat results..
 

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Discussion Starter · #37 ·
Hi.

The pockets are no deeper than a normal for a 16v piston, I think what makes then look deeper in the photo is that the rim of the 8v piston is much thicker. We did look at taking some of the thickness away from a 16v piston and using that, but it would have just made them too thin.

It was expensive in my mind to make 16 holes. We agreed on £180 for the work. A friend has a father who has quite a good garage engineering set up and it was perhaps suggested that he could do it. My thinking after speaking to the engineering shop was that the difficult part according to them, was creating the jig to hold the pistons in exactly the correct position, centre, hight and angle. I thought that seeing as I had obtained the pistons for nothing - and only having one shot at this per piston set - I would go with the engineering shop option.
 

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I also think your pockets are too deep, well, in your pistons :)
It's not that the rim of the 8v piston is higher, it is the middle that is lower than the 16v, see my pic in the second post in this thread, the pistons are lined up there at equal pin height. With standard cams you needn't to go deeper as with the 16v piston.
I heared of a DIY way of cutting piston pockets, it involves a spare head and probably block. A cutting tool is made by trimming an old valve leaving a sharp cutting edge and then spin this tool around in valveguide in the head with a drill, while the head is on the block with the piston fixed in the right height and orientation.
 
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