Which head gasket for 105TC head on 124 block?

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Lee67
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Which head gasket for 105TC head on 124 block?

Post by Lee67 » March 2nd, 2015, 5:08 pm

Hi all,

Hopefully there's a simple answer to my question: I'm using a Strada 105TC cylinder head on my 1592 block, should I use the head gasket matched to my block or the 105TC head?
My block is 80mm bore where as the 105TC uses an 84mm block (I think?) so what's the best solution?

All replies greatly appreciated.
Lee
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Guy Croft
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Re: Which head gasket for 105TC head on 124 block?

Post by Guy Croft » March 3rd, 2015, 2:06 pm

not 100% sure but the 84mm bore gasket might do the job. The gasket bore will be 85mm so the fire ring will stand 2.5mm away from the bores. The rest of the block is the same as the 1800 TC so cannot foresee any particular problem..

Important to note however that the larger inlet valves on the 105TC head will clash with the inlet valve reliefs so if you are on original 1592 pistons you could not fit it without enlarging the diameter of the inlet valve reliefs.

GC
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Lee67
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Re: Which head gasket for 105TC head on 124 block?

Post by Lee67 » March 3rd, 2015, 6:14 pm

Thanks for the advice Guy, I also have a complete 1608 engine which is in good order.
Given that to use the 105TC head I'm going to have to strip the 1592 down, would I be better off using the 1608 as a base engine? The head has been mildly ported and polished and I will be fitting a waffle manifold with 40IDF's along with the matching distributor and cambox.
I've heard people stating that the 1608 cams are the best of the factory cams, should I be looking to use the 1608 inlet cam in the mix?
Are pistons from 1608 and 1592 blocks interchangeable?

Thanks again,
Lee
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Guy Croft
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Re: Which head gasket for 105TC head on 124 block?

Post by Guy Croft » March 3rd, 2015, 8:16 pm

Hi Lee

you should have a read of some of these topics:

http://guy-croft.com/viewforum.php?f=3

The design of the 1608 piston VRs (valve reliefs) means they are only suitable for the 1608 - on that engine (and the 1438cc TC too) the valve centres are on bore centreline. On all the other others incl the 1592 cyls 1 and 4 have an offset and thus use a bigger diameter VR to allow use of the same basic head design as the 1608 on a longer block - if that makes sense. Effectively Fiat stretched the block to allow for bigger bores but kept the original patterns for the head. Albeit they also made some minor changes to the coolant galleries.

Irrelevant really but the 1608 and 1592 have different dome design. Different combustion chamber volumes. Different compression ratios - the 124 1608 ran 9.8/1, the 1592 ran 8.9/1 etc etc etc. All rather involved. There were three 1608 engines all with differing combustion chamber shapes and volumes - 124 and 125 and the Fiat Samantha too!

You cannot get new rings for those old designs now, all gone. You cannot simply put a used piston and rings in another bore and anyway pistons were size classed to individual bores as marked on the crankcase skirt A-E. Mix them up you are in trouble. The prep required on bores and pistons is so complicated you would frankly be better buying some GC forged pistons. I know how it is all done but I would never bother as it takes forever and don't let anyone tell you otherwise!

The 1608 cams are OK to use yes though I would not necessarily swap everything around.

Trying to figure out exactly what you have in mind really.

GC
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Lee67
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Re: Which head gasket for 105TC head on 124 block?

Post by Lee67 » March 4th, 2015, 10:58 pm

Hi Guy,

Basically I have recently bought a 124 Special T road car which I want to make a little quicker using parts that I already have laying around doing nothing.

It's currently fitted with a 1592 twin cam which as far as I know is standard (although it does seem to go very well for a 40 year old car with barely 100hp, it's almost as quick as my mate's 1600 MX5!), the car has covered only 33,000 miles from new.

Anyway, I have at my disposal a complete 1608 in good condition, as well as a 1995 in good condition along with a pair of 40 IDF Webers and factory manifold, the aforementioned 105TC head and a cambox and distributor from a 131/132. My first thought was "there's no substitute for cubic inches" so build up the 1995 engine with the head and carbs etc but have since read the negatives regarding installing this engine into a 124 - weight/height disadvantages, and the likelihood of it destroying my 124 gearbox ( I don't want to go to the lengths of fitting a 131/2 gearbox ).

So I now have 2 choices - build up my "spare" 1608 with the carbs/head etc and then pull the 1592 out and swap it over or pull the 1592 out, strip it and have the pistons machined and then rebuild with the IDF's and 105TC head.

The car is only to be used as a weekend fun car so fuel consumption etc doesn't really matter, I'm just keen to make the most of what I have available. I know full well that neither is going to give blistering performance.
Given the choice of a good 1608 or a good 1592 as a base engine what would be your choice?

Lee
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Re: Which head gasket for 105TC head on 124 block?

Post by Spider 1969 » March 5th, 2015, 8:49 pm

Lee,
From the engines you have available the 2L combined with the 105TC head and IDF40's should give you the most power and torque (130BHP as per 130TC which uses the same valve sizes and 40DCOE's) a so it would be my choice to overhaul and install this engine.
Regards,

Charles
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