Race Engine Forum UK

Hello.
I own a 1969 Fiat 125 with the original 1608 twin cam with 80000 miles.
I recently had a full recondition of the engine with new oversize pistons etc. The head was reconditioned too with new guides and seals. The whole engine is "standard" other than Marelli electronic ignition from a Fiat 131 and the oversize Fiat pistons.
Since owning the car for 4 years I have always been aware of cam/bucket noise. The clearances were checked and maintained at standard 18 thou for inlet and 20 thou for exhaust.
I recently decided to fit 2nd hand 1608 coupe cam shafts (9.6mm lift from the original 8.3mm) to increase top end power and obtained a set which I fitted myself with the help of the seller who is a mechanic. He told me the cams were checked by a cam specialist who confirmed they are "good". The noise is now much worse than before and on checking the clearances have found them to be slightly less than specified in the 125 manual. Can anyone advise if the problem could be caused by the cams themselves being worn or the clearances being too tight? Any help would be greatly appreciated. The cam boxes have been machined at some point.

Too loose or too tight are equally degrading on the cams.

Too loose and the opening ramp won't interact with the bucket the way it should and the result is nose wear.

Too tight and the ramps get worn out.

You should aim to set the cams within +/-0.002" of specified setting but I have been setting all the OE cams at 0.016" inlet and 0.018" ex for years and years without any wear or noise penalty.

Beware that the noise 'coming from the cambox' can equally as well be coming worn rod bearings....

G

Thank you for your reply.
I will rest the cams at 16 and 18 and see what happens!
When inserting the feeler gauge how tight should it be when assessing the gap?

What you don't want to do is try and force the gauge through as you might well be pushing the spring down - that of course won't give a true measurement. Offer up a gauge that jsut slips thru with minimum force and then go one 'thou' (0.001") thicker and one thinner. If you picked the right gauge first time the thick one won't fit and the thin one will 'fall' through.

G

I have set the cams at 18 and 6 thou. All good now. Nice and smooth and quiet.
Thank your for your advice.

clayton4 wrote:I have set the cams at 18 and 6 thou. All good now. Nice and smooth and quiet.
Thank your for your advice.

I'm sure you miss typed and meant .016"?

Yes, typo, .018 and .016 inch
Thanks!

I feel I should know......., but don't. Should tappets clearance be checked cold or hot?

Regards, James

COLD

G

Decisive! Thanks

For interest, I have noticed that the clearances increase on a hot engine, ie from 0.25 cold to 0.30, maybe slightly more hot. I presume the aluminium cam carrier and head, expands more than the steel valves?

James

Interesting if you're right - I always assumed they closed up!!!

Ah well, you (I) learn something new every day!

G

Just checked mine cold today. All 0.25mm as per cam maker instructions.

Will check them hot in a few days and give you a definitive.

Regards, James

Checked HOT and were all at 0.35mm. A fair way from their 0.25mm Cold position.

For info the engine is a 1500 SOHC Fiat. The tappets are standard, and I am using a "Catcam" adjusted to the cam makers clearance spec of 0.25mm. The Hot setting will be factored in by the cam manufacturers I am sure.

Regards, James