Help on pistons and cams please??

Road-race engines and ancillaries - general discussion
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nabihelosta
Posts: 94
Joined: December 14th, 2010, 5:37 pm
Location: Lebanon

Help on pistons and cams please??

Post by nabihelosta »

Hello Mr Guy and all this forum's members...
I am new to this awesome website, I am from Lebanon.
I have a '80 Fiat 132 2000, which I restored recently with a full bodywork. I won't talk anymore about it here, as I will soon open a new topic about it in "Readers Cars".
I am rebuilding my engine soon, and I need some advice and guidance, since I am an electro-mechanic, but I am specialized in BMW.
I currently have an Argenta Vx engine on it, but I omitted the Volumex ever since I bought the engine. For I have the AC compressor interference problem, plus I like going N/A :-) The engine has now its original setup, compression and camshafts, but runs on Weber 40 IDFs, on original waffle manifold. Lately, I doubted hearing the sound of a burnt valve, I checked the compression, the 3rd piston had only 40PSI, while all the others have 160PSI. So I'm overhauling :-D
Attached are the photos of a piston, which a friend of mine provided me with a set of 4 (for free, thank you Abbas). I don't know from what car they came. The dome is only 3mm high, but covers 75% of the piston's face. They are 84mm std, original Fiat/Lancia, and carry the following part#: 7589233. Any Idea from where they came? And how much compression do I expect on the Volumex head? (more than 9:1?)
I found also a set of camshafts, in a very nice condition, which I checked the serial numbers over the net, and doubted they came out of a 124 1800 sport, the ones with the 15/55 55/15 profile. The numbers are: 4333582 (intake), 4334852 (exhaust).
I also bought a set of adjustable pulleys online, so I'm dismantling soon, with the first thing on my mind, full balance of the bottom rotating parts.
Are my parts good enough? any horsepower expectancy on Weber 40s??
(N.B: I have the 131 Racing gearbox, short throw gearchange, and 4.1:1 ration diff from the 132 1800)
Thank you guys, I appreciate your advice :-)
Excuse me for the photos low quality, although viewable. I'm buying a hi-def cam on Christmas :-D
Top View
Top View
pist1.JPG (24.35 KiB) Viewed 9906 times
Side view: Dome height
Side view: Dome height
pist2.JPG (24.53 KiB) Viewed 9906 times
Last edited by nabihelosta on December 22nd, 2010, 12:48 pm, edited 2 times in total.
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Guy Croft
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Re: Help on pistons and cams please??

Post by Guy Croft »

Welcome & I can help but first please delete those oversize poor quality photos and replace with high quality under 400kb

See:

http://guy-croft.com/viewtopic.php?f=5&t=586

G
nabihelosta
Posts: 94
Joined: December 14th, 2010, 5:37 pm
Location: Lebanon

Re: Help on pistons and cams please??

Post by nabihelosta »

Done! Hopefully they are good enough :-)
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Guy Croft
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Re: Help on pistons and cams please??

Post by Guy Croft »

Be aware that although the bores are referred to as 84mm they are generally not exactly that and you are proposing to fit a set of class A pistons that are, well, sized for 84.00mm class A bores. The bore size class is stamped on the udnerside of the crankcase where the sump bolts up.

You better read this before you go any further:

http://guy-croft.com/viewtopic.php?f=3&t=254

GC
nabihelosta
Posts: 94
Joined: December 14th, 2010, 5:37 pm
Location: Lebanon

Re: Help on pistons and cams please??

Post by nabihelosta »

In fact Guy they are not exactly 84mm, I refered to them as so, just to make a notice that they aren't oversized (84.4, 84.6...). My machinist measured them and found tolerances going from 83.97 to 83.98.
Anyway it's a machinist job, as I'm intending to slightly polish the bores if tolerated, and work on the higher side of clearances tolerated for piston-cylinder wall, and rod bearings clearance. I already read a lot of technical topics in your website, I even printed the factory measurement sheet I gave it to the machinist so no worried there :-)
I just wanted to know about their CR, much more the engine expected CR if possible, on the Volumex head. I'm polishing the ports too, I think for a hot street build, I don't need more than a polish right?
And a small hint about the camshafts if possible too.
By the way, stamped on the pistons' faces the following: 3 pistons with the letters (C1), and one piston with the letters (D1). Are they of any importance?
Thank you Guy, I really feel you are interested and giving me attention :-)
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Guy Croft
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Re: Help on pistons and cams please??

Post by Guy Croft »

Nabil, hi

you should try and get a 'handle' on the process of detemining the CR, the attached download can be used to 'fill in the blanks', essentially you enter bore, stroke, deck height, gasket thickness and diameter, burette the head and piston dome, measure the compression height of the piston crown and valve reliefs etc etc. I've put in what I know, like Vx head volume. You enter a CR and adjust it till the piston dome matches the one you have and I don't know what it is exactly, ex Lancia Delta 1600 maybe, say around 10cc. You can estimate the dome volume from this calculator:

http://grapevine.abe.msstate.edu/~fto/t ... /cone.html

Don't forget to enter radius, not diameter.

Thos piston codes may well be the broe size classes and you want a maximum of bore-skirt clearance of 0.002" really, more than that and you risk cracking the skirts and ending up massive ring end gaps. You should try and match pistons to bores to get the best minimum clearance but this needs a bore gauge and micrometer. Beware of the worn section of the top of the bore, the ridge there will knock the new rings to pieces and it should be carefully smoothed with coarse then fine carborundun before honing at 180 grit FlexHone, if you don't have one buy one because any other bore prep method will make the bores tapered and so oversize the engine will 'drink' oil. Cleaning the bores with string detergent and hot water is vital, not to mention drying and oiling to prevent corrosion.

I am not a fan at all of putting new std pistons in old bores, I have done it more than most but am very reluctant to advise on it. I think there is probably enough in the GC V/W to guide you but you have some reading to do. I could write a book on lost-cost overhaul methods but the results will never match the more expensive (eg: rebore) way..

I can tell you the CR will be OK, at least. It might be worth machining the block down if the pistons don't run flush, get rid of that typical 0.5mm clearance they have in OE trim, though where they will sit not being from a 2 liter unit I don't know. Cams from any normally aspirated 2 liter will do. I'm not going to guess the power, sorry, too much will depend how well you prep and set it up.

An awful lot of 'long-distance guesswork' needed by me here. I strongly recommend you try and study the subject of engine rebuilding, much is written here and I have published 2 books & there are many others and the techniques are common to most engines. Far too get over-excited about building up as fast as possible skipping vital steps many plunge in with little knowledge and expertise and end up with a pretty second-rate unit that pleases no-one and wastes money.

GC
Attachments
Nabil.xls
(20.5 KiB) Downloaded 435 times
nabihelosta
Posts: 94
Joined: December 14th, 2010, 5:37 pm
Location: Lebanon

Re: Help on pistons and cams please??

Post by nabihelosta »

thank you Guy.
I will have all these in mind when starting to dismantle, and let you know everything and guide me step-by-step
Thank you :-)
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nabihelosta
Posts: 94
Joined: December 14th, 2010, 5:37 pm
Location: Lebanon

Re: Help on pistons and cams please??

Post by nabihelosta »

Hello Guy...
Hope you enjoyed Christmas with your family.
Just a thought to treat when you'll be back from your holiday:
I own a rare SEAT 132 1920c.c. crankshaft, having a 86.5mm stroke. Just a thought passed by my mind a moment ago...
What about building a hi-spec SQUARE engine?? 86.5mm stroke, 86.5mm bore? Is it possible to do? Are there any pistons useable out there, or can I order a set from CP pistons? (By the way I'm a regular costumer at CP, I order a fairly big amount of BMW pistons each month). Does the block allow to be bored to 86.5mm?
Would it revv better than a 90mm stroke engine? What about cylinder head gasket, and combustion chambers?
Surely a great project to do, only if you think it's do-able!!
Happy holidays :-)
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Guy Croft
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Re: Help on pistons and cams please??

Post by Guy Croft »

The biggest I've done (Gp4 124 16v) is 86.10mm bore, so I figure 86.5mm is do-able.

You'd have to get forged pistons made, sure, allow at least 0.5mm clearance from piston to gasket fire-ring or it will hit. You can'tget 86mm bore gaskets so you will have to use one at usual 85mm fire-ring bore and I have some heavy-duty ones for that, I'd definitely use my race bolts with it though.

Remember that the bigger bore reduces the amount of contact between block and fire-ring.

G
Attachments
putting together a Gp4 16v 124, the block and head are genuine Fiat-Abarth, the bores are 86.1mm and owner Mick Wood had one Astadur 86mm bore gasket for it. I CANNOT get these anymore.
putting together a Gp4 16v 124, the block and head are genuine Fiat-Abarth, the bores are 86.1mm and owner Mick Wood had one Astadur 86mm bore gasket for it. I CANNOT get these anymore.
MW_16v 02 block build (3).JPG (116.58 KiB) Viewed 9721 times
nabihelosta
Posts: 94
Joined: December 14th, 2010, 5:37 pm
Location: Lebanon

Re: Help on pistons and cams please??

Post by nabihelosta »

Hello Guy
Hope you had the best holidays ever, and wish you a very happy new year.
While I was making my tour in the local market to gather all necessary parts for my rebuild, I found by pure chance a very rare (at least here) head gasket with the following inscription: Spesso Racing, Ritmo 130TC, Gruppo A. The part advisor (which is a friend of mine), told me that it's a rare item, he once ordered two of them, one was used on a hillclimb car, and the other is laying here dusty for some 10 years. I told him to keep it for me for a couple of days, just the time needed to ask you about it :-) It's priced at 75$.
Is it worth its price? Is it really this good and a necessary plus for my hi-comp engine? Is it too much thicker than the OE gasket that it will drop my compression?
Please advice, before I buy!
Thank you.
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Guy Croft
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Re: Help on pistons and cams please??

Post by Guy Croft »

I never get into discussion of the influence of gasket thickness on CR, I measure and put the info into the CR calculator.

The stronger gaskets are usually quite thick. Nothing wrong with the Spesso item, but included in the price will he tell you the recommended head bolts and settings as I would?

G
nabihelosta
Posts: 94
Joined: December 14th, 2010, 5:37 pm
Location: Lebanon

Re: Help on pistons and cams please??

Post by nabihelosta »

I don't think so... After all he's a part seller not a mechanic.
Is there any special head bolts to be used? I thought the OE were OK i don't know... never been through that rebuild on a Fiat ever!
You mean some special made bolts or just original items from another cars maybe stronger?
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nabihelosta
Posts: 94
Joined: December 14th, 2010, 5:37 pm
Location: Lebanon

Re: Help on pistons and cams please??

Post by nabihelosta »

Reviving this thread just some days before dismantling and starting to build my engine.
I bought today another set of pistons, standard bore, with the 6mm height dome, out of a Lancia 1800 engine. They look extremely new and in excellent condition. Anyway I'm getting them measured by my machinist on monday.
Question: I found a 130TC head, fully ported and polished, with 46mm/38mm valves from BMW M30B35 engine (535i). The guy would give it for 200$. Logically, it needs dismantling, cleaning, valve stems, checking for bend, and (if ever I bought it) new TRW valves, same as fitted (which I have on the shelf). Does it worth 200$? Couldn't I do the same job on my head, or going this BIG is really useless? Is the 130TC head really "better" than the Volumex one? Does it have bigger chambers? What do you advise Guy?


Thank You :-)
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