Technical camshafts

[brokenwrench]

i have a 71 124 spider, attempting to rebuild. machine shop says my cam bearing journals are .002" over spec. book says to replace if excessive wear. How much is "excessive wear"? can i run these cams , or do they really need replacement?

 

[Greyjag]

OK who is the expert? I would say the engine builder. Listen to their advice

 

[124BC1]

Here's the factory specs:-

Personally, I'd reuse the existing cams providing the cam lobes are still good and that the engine oil pressure was ok beforehand.

(excessive cam bearing clearances can contribute to lower than normal oil pressure, as can excessive auxiliary shaft bearing clearances along with the other usual suspects - worn crank bearings, oil pump etc.)

 

[s130]

Personally, I'd reuse the existing cams providing the cam lobes are still good and that the engine oil pressure was ok beforehand.

(excessive cam bearing clearances can contribute to lower than normal oil pressure, as can excessive auxiliary shaft bearing clearances along with the other usual suspects - worn crank bearings, oil pump etc.)

I'm inclined to agree with this if the oil pressure is good (at idle) and the rest of the camshaft and lobes are ok.

Generally speaking it is crankshaft wear/bearings that lead to loss of oil pressure. Also the forces involved at the crank are far greater than those at the cams.

If you don't plan on revving the nuts off the engine then some wear in most things is OK. How much wear is a different question. Noise and vibration are the usual factors.

All this said, if the cams are already stripped out and you are also having other refurb work going on then replacing the camshafts come down to price, availability and peace of mind.

 

[124BC1]

I'm inclined to agree with this if the oil pressure is good (at idle) and the rest of the camshaft and lobes are ok.

Generally speaking it is crankshaft wear/bearings that lead to loss of oil pressure. Also the forces involved at the crank are far greater than those at the cams.

If you don't plan on revving the nuts off the engine then some wear in most things is OK. How much wear is a different question. Noise and vibration are the usual factors.

All this said, if the cams are already stripped out and you are also having other refurb work going on then replacing the camshafts come down to price, availability and peace of mind.

Well said.
I had written a lengthy response for post#3 but deleted most of it (didn't want to put the 'listeners' to sleep > ).
Op didn't say whether he was having the entire engine rebuilt or just the cylinder head, so I assumed that as he had only asked about the cams, he was only doing the head.
On those twincam engines, both the bearing bores in the aluminium cam housings and the camshaft journals can wear, so fitting new cams (which currently seem to cost $400 - $500 or more, I saw a set of 'sports' cams for $1424!, from suppliers in the U.S.) might not bring the cam journal to bearing bore clearances back to spec. So then what, fit new cam housings as well? - afaik, new cam housings are no longer available? and second-hand ones are pricey and may not be any better than Op's existing ones.

I recommended re-using the existing cams with the same provisos as s130, plus reckoning that the cams could always be changed later without disturbing either the engine or cylinder head in the car if it proved necessary to do so.

Also, in my experience, those older twincam engines didn't have great oil pressure possibly due to the oil pump being driven from the auxiliary drive shaft, (i.e. at the same speed as the cams) at half crankshaft speed (unlike more modern engines). It wasn't unusual to see the oil pressure warning light flickering when the engine was at idle speed after a fast run or in very hot weather (iirc ,the w/l comes on at < 7 p.s.i.) and the dash gauge wasn't very accurate either.