15 replies to this topic

[JCP]

Morning guys,
Bit of a random question which I think I already know the answer to.
Is it possible to find out which cam is fitted to an engine while the engine is still in the car, without having to strip it down?
I ask as I'm recommissioning a 1983 998 Mayfair, and have found it has a 12g202 big valve head and a harmonic damper fitted. I spoke to the previous owner who fitted these, and he says he thinks he put in a 286 cam but can't remember.
I am inclined to believe him that it does have a sportier cam in it, 286 seems a bit wild tho, would there be any hints or give always that it does have a sportier cam that I can look/listen out for without stripping back the engine and visually looking i.e. Lumpy idle, shorter or longer rev range?
Thanks

[Spider]

Yes you can. You'll need to remove the radiator to do it with some accuracy.

 

When Photobucket finally loads up, I'll post a couple of photos

[Spider]

(3 days later....)

 

You'll need to fit and time in a degree wheel to the crankshaft

 

 

and a Dial Gauge to the valves. I do the Inlets first, then the Exhausts

 

 

Being an unknown Camshaft, I would suggest logging valve lifts every 5 degrees and you should be able to work it out from that.

[carbon]

Also as a first stage check you can measure the lobe lift of the cam - measure pushrod lift with DTI or similar on inlet lobe.

 

This does not tell you definitely which cam is fitted, but will give some good pointers. If inlet lobe lift is 250-265 thou then it may be a MD266 or similar. 270-300 thou is into SW5, Piper 270, RE13, MD276, SW10 territory.

 

Anything over 305 thou lift at inlet lobe is likely to be MD286 type profile. This will make for a very sporty 998 driving experience.

 

Valve lift at overlap also will give a useful pointer to type of cam installed.

Edited by carbon, 08 April 2017 - 09:32 AM.

[mini13]

As above, but as a quick shortcut you could just check the max lobe lift on an inlet and an exhaust lobe, and check against the 286 specs

 

ah beaten to it! lol ^^^

Edited by mini13, 08 April 2017 - 03:32 PM.

[JCP]

Thanks for the replies, great that I can check without the need to strip everything down, I did think that was my only option to find out. It'll be interesting to see what (if anything) I've got at least.

[mini13]

also, just a thought, but if your running a belt drive you would be able to whip the cover off and check the stamping on the end of the cam.

[Spider]

One other thing when checking - be sure to ONLY turn the engine over in the direction that it normally runs.

 

You won't hurt or damage anything if you don't, but the measured results will be way off.

[JCP]

Not running a belt unfortunately, thanks for the tip Moke spider that could of given me a headache reading the wrong results!

[ACDodd]

Far easier way which does not need a protractor is to use 2 dial gauges and measure the lift at split overlap on cylinder no.1 directly at the pushrod. Post back this figure together with the lobe lift fir the intake and I'll let you know how this cam will perform.

[JCP]

Hey all, I checked the lift at no.1 inlet on the push rod and got a reading of .273thou I then got distracted by the new born and ended up putting everything back together before I took any other measurements, Doh!
Anyway would I be right in saying that this is not a standard cam? Possibly 276, SW5 or equivalent?

[ACDodd]

Not standard, could easily be a worn cam. No use without the other figures.

Ac

[Spider]

Not standard, could easily be a worn cam. No use without the other figures.

Ac

 

Which is exactly why I suggested you'd be best off to remove the radiator, fit a protractor and used a dial gauge to map the cam profile. Honestly, unless it is known to be a fairly new camshaft, anything less is a waste of time and misleading.

 

The car that I posted the photos up of above ^ was reported to have very poor performance, given that is was a fresh build of a 1380. I suspected the way it drove that it had a cam profile problem and on measuring it, was found to have a hap-hazard ground cam.

[JCP]

Ah poop, ok when I get a chance I'll get back out and have a proper measure.

[Retroman]

(3 days later....)

 

You'll need to fit and time in a degree wheel to the crankshaft

 

 

and a Dial Gauge to the valves. I do the Inlets first, then the Exhausts

 

 

Being an unknown Camshaft, I would suggest logging valve lifts every 5 degrees and you should be able to work it out from that.

 

We all like some ingenuity....hows the cam degree wheel attached?