MG T-ABC

Hi all,

I'm looking for data on camshaft life. Some people seem to run a standard "flat tappet" camshaft forever, while others wear them out quickly. Just recently I installed a new camshaft in a relative's XPEG and it failed almost immediately, before the break-in was even completed. The tappets looked like they had 100K miles on them (it appears they weren't hardened properly) and the camshaft itself appears to not have enough offset to promote rotation of some (but not all) of the lobes. That has me wondering, is the reputation of these engines eating camshafts undeserved? Is the problem the camshafts themselves? More specifically, certain brands of camshafts?

When I install a camshaft I always check for tappet rotation, but surprisingly I've learned that not everyone does. Nor do most people ever remove the tappets to make sure they're healthy, no matter how many or few miles on them. When I discussed this failed camshaft with the retailer, he contacted his manufacturer (who he has not told me the name of) and they seemed shocked that anyone would inspect the parts after installation. I've always treated this as SOP. They have since admitted the problem and are changing the design of their camshafts. I shudder to think how many of these defective cams and tappets are out there, with the owners completely unaware their brand new tappets are falling apart while they drive.

So my question to the members of the group is, how many miles are on your camshaft, and do you know what the state of the tappets currently are? A make/model of camshaft would also be useful data.

I know about roller camshafts and their pros/cons, but prefer to keep the topic on traditional camshafts.

PHOTO: The tappets below had 30 minutes of break-in on them, nothing more.

I cannot prove the mileage but I have no reason to believe the standard camshaft that came out of my engine was not the original one. In which case it will have done 25,000 miles and shows no appreciable signs of wear. I replaced it with a new fast road camshaft which is more substantial ...but whether it will last as long only time will tell.

I have since learned that contrary to the advice I was given at the time, the original cam would perform just as well with a supercharger, so I may have wasted my money.

hi Steve - those tappets definitely look suspect! We have discussed this many times over the years: the originals were cast iron which was heated up (don't ask me to what temperature, others or Mr. Google will know) then placed on a cold iron (or maybe steel) plate in a process called Chill Quenching: this hardened the bottom and can sometimes be seen as a different coloured band. This was often nearly 1/4" wide, and meant that they could be re-ground (several times) without going into the softer material. Yours look as if they were surface-hardened (typically 15-20 thou deep) and might very well be steel. I have removed many tappets which were not rotating (they had the butterfly pattern showing that they were merely oscillating), and reground them. There was also talk about putting a slight dome on them to encourage rotation, although I never got around to doing this.

We had a talk about cams by a certain Mr. Newman, several years ago at one of our T-register Rebuild seminars: this was discussed. I cannot remember all the details, and AFAIK there was no record made, but I think he said that they were making tappets from tool steel. But their website (newman-cams.com) lists chilled iron ones at 72GBP for 8, or induction-hardened and nitrided EN19 steel for 144GBP a set. These are for "competition" use but would probably last almost for ever in a road car. They also offer 6 types of cam and valve springs

Roger

The vendor isn't saying who the manufacturer is, but I'm pretty sure that it's Newman. The tappets pictured above are the expensive upgraded ones, so something definitely went wrong with them.

It could be that the vendor did not send you what you ordered.

According to WKF Wood (p8 of 54) http://www.ttalk.info/WKF-Wood-XPAG-Engine-Book.pdf
The lifter bore should be .906 inch (23mm) and the tappet clearance should be .0015 inch. In other words,
the tappet dia. should be .9045 inch.

I found a lone non-rotating tappet to be .905 inch. A single replacement tappet ordered from AS matched the other
rotating tappets at .9045 inch. When the replacement tappet of correct diameter was installed, it rotated.

Hi Steve,
I suggest you all stop guessing and find a frendly metalurgist who will give you a report by sectioning your now scrap tappets typically you need a minimum of 0.040 inch deep case to support bearing loads like the camshaft produces. As Roger says it looks like a shallow case. Did you check by the way that your valve springs are not getting coil bound you need a minimum of 0.010 inch between coils at full lift.If it proves shallow go for a refund!!!
John

Thanks for the data. The cause isn't much of a concern, all the parts are going back to the vendor. They can spend the time and money on it if they like. The old tappets were rotating so I figure that eliminates the block as the problem. The main concern is how many camshafts fail in short order in these engines. All these years of having a bad reputation, and I wonder if incorrectly designed camshafts and/or tappets have been the issue all along.