Fiat DOHC cambox compatibility.

[miro-1980]

We have faced issue of cambox compatibility on Fiat DOHC 2.0 liter engines .

I have done research on this (with GC assistance) and here are some tips which members might find useful:

Please correct/add/comment as as required:

First of all 124, 131 and 132 camboxes were compatible and can be applied across all these models 2.0 DOHC models.

Actually the camboxes used in 124, 131 and 132 had makings either : "124" or "132". Note: no 131 markings at all. .

See an example of 132 numbering:

C.jpg (39.97 KiB) Viewed 4746 times

.

There appear to be two problems trying to apply a galleries from different models ( i.e. Ritmo or Lancia) which of course which had
transverse positioned engine often tilted as much as 20 degrees.

One : the oil drains were propositioned differently, which was to adjust to the tilt so that the oil flow would be proper.

For instance using cambox from Lancia will cause the camboxes to overfill (excessive accumulation of oil in the camboxes).

NOTE : GC indicated that increasing the diameter of the oil drains will take care of the overfilling problem.

See an example of a cambox from 132 and a Lancia (I believe).

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The other problem are size and positioning and shape of oil channels on the bottom of the camboxes.

I have no picture of the ones which - I am told - are positioned differently. (ADDITION OF A PICTURE WELCOME !)
The problem of these applied to a 123,131 or 132 is a good risk that the head gasket will not keep the coolant and oil separated which as well all know can
be quite hazardous FOR THE WHOLE ENGINE .

See example of the "proper" look of these for 124, 131 and 132.

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Another element to look for are openings in the back of the cambxes.

See examples fit for 123,131 and 132 and not.

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And finally please remember that the factory tolerance for the cambox oil bearings are very tight ! 0.02 mm

See the picture showing specific numbers:

measurements.jpg (49.38 KiB) Viewed 4747 times

On the top of this GC has brought up a very good simple and quick test.

These camboxes are often used beyond application, especially for hi performance. The tolerances are really very small , far too small to be
assessed with a naked eye. We often have to make the decision to buy
or not based on a picture only.

The way to do it is to look/ask for presence of any scratches on the oil bearings (supports for the camshafts), especially on the rear one.

The rule seems to be : scratched is scarap. !


Comments corrections, additions very expected!

Miro

[Guy Croft]

Good article Miro, it's nice to see a member posting a 'GC style' 'How To' for no other reason than to help others.

Scratched is scrap? No.

Some scoring/scratching is quite usual and is the result of:

- dry start
- dirt in the block oil feed galleries being pumped into the cam front housing (very common esp if the block has been 'dressed' with carborundun paper and the holes not plugged or cleaned out)
- cam belt too tight (often in conjuction with dry start)
- oil contaminated with gasoline or 'never' changed, ie: worn out with contaminants..

A used front cam journal housing should always be cleaned up either with a fine FlexHone (240 grade or finer) or some coarse then fine Scotchbrite mounted in a little mandrel (wooden dowel with a slot in the end will do perfectly well) and spun with WD40 using a hand drill. The direction of rotation should be the same as the cam, ie: clockwise from front (as polishing a crank) so that the process doesn't raise the metal in direction of rotation. Bit like combing an animal's fur, brush one way and it flattens, the other causes it to stand up. If the scoring is reasonably localised it will not cause any problems, the main thing is to ensure that there aren't any 'raised' areas that will rub on the cam: sub surface is OK. This is true of cranks too and used cranks often exhibit scoring or grooving. Judging what is fit-for-use and what is not is really a question of experience but I have only ever junked about 3 cam boxes in my life, so when I say scoring isn't too much of a problem you can be sure I mean it.

It is also important to use a flat carborundun stone to 'dress' the cambox lower mating face and that area of the head too. I don't recommend machining them, the parts distort in service and they distort together. If you machine one the cam may bind when you try to turn it. I don't recommend machining the cambox to fit cams with small base circle simply because most engines I see get 'retuned' later on (with cam swap) and it can be a real problem if the cambox has been machined - in other words, a bit like milling the head to death (to try and raise the CR) - it's an irreversible op you'd be well advise to avoid. If you don't dress the mating faces you might miss a score across the region that the gasket has to seal. If you have a deep score that gasket will leak unless you put a bit of silicon sealant in that area.

If you get oil leakage from the cam nose seal, there is a very good chance it has been caused by debris in the cam nose journal. Even the minute amount caused by 'pickup' betw cam and housing will wreck a cam seal in minutes.

I could write a whole book about 'dressing' and prep. It's 'fitting' in the old sense (as used in the trade qualification 'fitter/machinist'). I deburr camboxes all over these days, use fine Scotchbrite wheels in the cam bucket housings, do the center and rear journal housings with the Scotchbrite/drill too. And that is only after decarbonise, clean, beadblast. So prepping a cambox 'GC style' takes about 2 hrs if you do it my way.

And I still get folk coming here expecting my shop to be, dunno, a 'reconditioner' and when they see what really goes on here they stand there saying 'Oh, I won't be racing it', as if to say there should be a second (rate?) standard of work from me on his engine just so he can save a few bob. I do get fed up with trying to justify what I do..

Dressing and prep: Nothing at GCRE is done for cosmetic reasons, and there is a reason for every op I perform with 20 years of exp behind that call.

GC

[miro-1980]

Guy,

Thank you very much for kind words and your additional detailed explanation on the scratching issue.

I have benefited so much from your articles, responses, advice and detailed explanations to my questions as well as those posted by other members that I have felt only too happy to make but a small contribution to the forum.

After all we cannot expect (as we all do anyway) that you will answer all the questions and cover all issues at any given time. DOHC being an ingenious construction is as simple as it is a complex machine makes this impossible. Especially as this is run by one man and in his spare time from business. I rate this forum as an extremely valuable, public service to the DOHC community. For this we are all very grateful.

I have to say the dealing with a variety of engine specialists over some 40 years, I have never encountered anyone who - like you - is openly sharing his experience gathered over some 20 year of rebuilding and modifying these engines. As far as I am concerned you are the only one. No wonder this forum is an Elite Place and the name of GC is known and respected by all those who know anything about DOHC’s.

I would never risk writing anything really like your - "GC style" "How to article" but the issue I wrote about seemed simple enough and at the same time seemed useful to others I decided to share what I learned. I am glad you did not treat my article as trying to step to your shoes.
I wish I had your knowledge and experience, but the fact is that I will have to remain just a student of yours!

Miro

PS: The 8 valve head prep DVD set I have recently received from you is absolutely stunning. Even though there is some 5 hours of film on it I have watched it all in one afternoon/evening. Could not get my eyes off of it. Having studied both your book very thoroughly, and having read and studied practically all your articles on this site I though I new a lot. Well the DVD's proved me wrong.[ Only watching it gave me a real idea of how to do it the right way.

I did not realize for instance there are so many elements that go into simple head cleaning, let alone flow testing or valve guides removal and installation, valve seat preparation, and most of all that porting took so much detailed care. Having seen a life example of the regime you apply in head building I am beginning to appreciate why the CG engines perform that well in sports!

Your step by step instruction backed up by you actually showing how you do were crystal clear. I have neither the time nor facilities required of a proper garage. If I did , I would not hesitate doing it myself! I was truly amazed and fascinated watching it.

Thank you again for the DVD production. In my view anyone who has not seen it cannot claim to have any real knowledge on how to do it the CG way.

PS: Guess who's gonna build my next engine! Having seen how you do it I want nothing less then the GC standard. I am too poor to go for second best !

M