CAM WEAR PROBLEMS

I alluded briefly to the CVH cam wear problem in the introduction. As this crops up so often on newsgroups and emails I'll expand on the matter. The CVH cam is lubricated by the oil that drips through little brass bushes next to the rockers. Even this limited supply can disappear if the bushes clog with carbon due to infrequent oil changes and cheap oil. Also the valve spring is extremely stiff compared to other engine designs. It generates a load at full lift of 220 lbs compared say to 125 lbs for a Pinto or Mini engine, 150 lbs for an MGB. This high spring load is necessary to control the heavy rocker and lifter and still only allows about 6,700 rpm before valve float starts. To compound the matter, Ford didn't use the best available material for the camshafts. "Chill cast" camshafts last several times longer than the induction hardened material used in the CVH.

Cam wear is therefore a fact of life with the CVH. Most other types of engine show little or no cam wear in normal use and if wear does start then it tends to accelerate exponentially leading to rapid failure. Standard CVH cams wear steadily from the moment they are fitted. I've never stripped a medium mileage road CVH engine that didn't have considerable wear on the lobes and lifters. The problem is worst on cylinder 4 next to the fuel pump lobe. This is nothing to do with the urban myth about cylinder 4 being furthest from the oil pump. Whoever started that one wasn't the world's deepest thinker. The oil supply runs up through the block between cylinders 2 & 3 so in fact cylinder 1 is as far from the pump as cylinder 4 despite being right above it. In fact there is a design fault in the engine which means that the cam lobes on number 4 are not properly positioned relative to the lifter bores.

Cam wear starts to take place about half way up the lobe. It then leads to dishing of the lifter base and loss of material over the cam nose. As the lifters dish, a sharp lip is created round the base of the lifter which means they often won't withdraw through the lifter bore. If this occurs then under no circumstances try to graunch the old lifters out with a pair of pliers. You'll score the lifter bores and ruin the oil pressure to the lifters. Raise the lifters until they are clear of the cam lobes, remove the cam and then push the lifters into the head and get them out through the distributor housing bore. Check every lifter bore for wear. On neglected engines the bores can wear and this means the head is scrap. Take a lifter and turn it upside down so you aren't inserting the lip into the bore - better still use a new lifter if you have one. It should just slide into the bore with no appreciable rock. Copyright David Baker and Puma Race Engines

There is NO, I repeat NO point in fitting new lifters to an old cam in the hope of fixing a noisy engine. The new lifters will be reduced to scrap by the worn cam lobes within minutes of starting the engine. Replace everything, clean the brass lubrication bushes and if the head is really badly clagged up (which they tend to be) then remove the head and have it chemically cleaned to remove all carbon deposits from the oilways. Then fit and run the new cam and lifters in properly - use plenty of cam lube on the lobes and lifter bases and don't let the engine idle for the first 15/20 minutes - keep the revs at around 2000 which gives the cam a chance to bed in and work harden. Change the oil and filter too (flush the engine out as well if you want to do the job properly) - all that material that wore off the old cam lobes is down in the sump gradually wrecking the crank bearings and oil pump.

Fix a worn cam problem properly and you'll get as good a life out of the new one as you did from the original. Get it wrong, leave the oilways blocked, fail to use cam lube or run in properly and you'll be doing the job for a second time within weeks.

http://www.pumaracing.co.uk/cvh.htm