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MG MGB Technical - pitted camfollowers
| Last week I disassembled my MGB engine. To my unpleasant surprise 3 out of 8 camfollowers were pitted. These followers and camshaft were only 2000 miles used. I have had similar problems with my previous camshaft and followers (also only 3000 miles old). In both situations I carefully bedded in the cam during the first moments of operation (15 minutes at 2000 - 2500 rpm, special Kent lubricant on the cam and followers) and I use standard valve springs. How can I prevent these problems? It makes me rather desperate. |
| P.Brokke |
| Define "pitted". Normally, pitting is the random removal of metal through rusting. When the rust is removed, you will have pitting underneath when the rust has been severe. Cam followers (tappets) should be of hardened steel and should be very resistant to rusting. It sounds to me like you have a problem with either the material the tappets are made from or the heat treatment. I would suggest you contact the manufacturer or retailer of the cam and tappets for guidance. Les |
| Les Bengtson |
| Les, The tappets are not pitted by rusting but are pitted during operation. Indeed tappets are made from hardened steel, but still they were pitted. Peter |
| brokke |
| Peter. It sounds like bad metal in the tappets or crud in the oil system. I can see dishing if the heat treatment is improper, but not pitting. You need to return the tappets to the retailer or manufacturer and ask them what the problem is. The only way I can see pitting happening is if the metal is not correct for the application. Who did you get your tappets from? Les |
| Les Bengtson |
| I've seen some pretty scary examples of "pitted" cam followers (even to the extent of "hollow ground" versions) and it does not necessarily have to do with faulty materials or grit in the oil. However, there have been a number of instances recently with poor quality control of the later cup type tappets and I don't know of any easy solution for that one. Sometimes the fault can be a poor location of the bore in which the tappet rides, or incorrect cam thrust clearance. If the lifter does not line up with the lobe properly, it will not be able to spin as needed and will wear more quickly than if it were lined up properly. Unfortunately, unless you have the means to blueprint the cam bores, there isn't much you can do about this but to ensure that the cam is shimmed up correctly and hope for the best. Another thing you can do, is to make sure that the bore has a proper finish. There are two ways to do this and my favorite to date is the flex hone of the proper size. 180 grit will work fine. The alternative is a small brake cylinder hone. I don't have the clearances in front of me, but I think they are in the range of .0006" - .0008". We are looking into the possibility of blueprinting the cam bores on all of our engines in the future and using Ford sized lifters. This will not only reduce the chance for lifter failure, but also allow a more radical cam profile for the same duration, both of which are a needed commodity on the MGB. If you are getting the parts from Kent, I'd call them and see what they say. Sean |
| Sean Brown |
| Some damaged lifters I removed from a spare engine from a parts car can be viewed at; http://albums.photopoint.com/j/ViewPhoto?u=817566&a=14002307&p=56494316&f=0 You will need to copy and paste to view the photo. The engine was recently worked on, new pistons, rebore and new camshaft. I'm not sure if the lifters were replaced because the work was done prior to my getting the car. The worst lifter came from no. 4 intake and the other was from the no. intake. The third lifter looks like it was not rotating because of the wear pattern it shows. The mechanic or person doing the work left some swarf in the engine, the oil pressure relief valve spring was too short and oil pressure was about 35# with engine warmed up. So the pitted lifters may have been due the poor quality work. For some additional information on lifters and their hardness and compatibility with Crane/Moss cams you may want to read the the following. Scroll down to, Camshaft Recommendations (Street Performance) and Camshaft Lifters: http://www.mgbmga.com/tech/mgb20.htm I recently purchased a set of lifters, they were in Moss packages, the packages had a made in England label on them. They really look like junk, that is not to say they are defective, they may be ok. Today I was helping a friend on a TR-8 engine and the lifters for it look like a precision item as they should, I realize they are hydraulic, but manual lifters should also be a precision part as they take a beating. Clifton |
| Clifton Gordon |
| Above should read as follows; The worst lifter came from no. 4 intake and the other was from the no. 1 intake. Clifton |
| Clifton Gordon |
| Hi Peter As I explained to you in an e-mail...the lubricating oils can leave somewhat to be desired! We always use a molybdenum disulphide based inorganic spray or organic based paste for our followers and lobes. Another reason for failure, which is very common, is caused during 'winter' storage. If the car is laid up with old oil any metal to metal contact under pressure (cam/followers, piston rings to bore) are subjected to some pretty vicious acid attack from the content of the oil...leaves lovely black pits! Cam followers can also be subjected to Herzian failure....a cyclically induced failure where lumps of metal leave the lobes/followers at the penetration depth of any metal hardening process. Peter |
| Peter Burgess |
| Hi, So far, thanks. I have forgotten to tell that I am using modified MGC followers in my engine. These tappets are larger in diameter. This was done after I have ruined 2 camshafts. The engine shop who did the work (Dymo Track in Holland) had good results in terms of reliability with this modification. But again, the followers are pitted (so actually it is my third camshaft/tappet combination). The Kent co. really likes me. I am also thinking of a cryogenic treatment of the followers. Are there people who have experience with this treatment. Peter |
| Peter Brokke |
| I found this an interesting thread, and in going out to British Automotive's site (see Clifton's posting above) I found this quote which seemed pertinent to the question at hand. "Camshaft Lobe Lifts "We recommend that lobe lifts be kept in the region of .290" max or less, remember that high lobe lifts come at the expense of reduced lobe heel diameters and also extreme pressures at the lobe nose/lifter interface.." If I understand this correctly, higher lift cam lobes will hammer the lifters harder because of the smaller contact area and faster momentum inherent in the shape of the cam lobes. If a hardened cam lobe/lifter has any weakness at all, or the pitting described by Peter Burgess, then my assumption is that you would get a similar accelerated wear as you have. In essence, the wear you are sustaining may almost be inherent in the combination of design elements used - IF this is anything like that which YOU are using. Just a thought. |
| Bob Muenchausen |
| Hiya Peter You seem very unlucky....what oil type and grade are you running? Tuftriding the cam and followers may be a better way of preserving them. Peter |
| Peter Burgess |
| Hi, I am using Penrite 20w50. I had planned to switch after 2500 miles to Motul synthetic oil (15w50). There are people telling me that Penrite is not the oil to use. But, there has to be more then 500.000 B-engines owners who are using the cheapest oil they can get. So?????? Peter |
| Peter Brokke |
| Hiya Peter I managed to denature fresh Penrite 20/60 oil in 60 laps around Cadwell on a test day....personally I prefer Silkolene Pro4 semi-synthetic. MGB ( and for that matter...most older engines I can think of ) have oil galleries more suited to the thick oil-types such as semi-synthetic...not fully synthetic...also bear in mind that gears need protection and synthetics were not designed for this job...results in lots of cam gear wear! Just a thought...do you have a crankshaft scrapper device fitted? Peter |
| Peter Burgess |
| Hi, There are people in the race business (english and dutch) who are very clear in advising Motul synthetic oil because it SAVES the camshaft gears, lobes and lifters !!!!!! It is becomming a little bit confusing....... What is a crankshaft scrapper device? Somehow I think the problem with my engine is a poor location of the bore in which the tappet rides. Some lifters look like they were not (not enough?) rotating because of the wear pattern they show. Others were 'correctly' pitted. I think Sean Brown is making a point here. I think of looking for an other block. Peter |
| Peter Brokke |
| Hi Peter I meant crankshaft scraper...not scrapper! It is for removing excess oil from the crankshaft...very risky though...as the cam is splash fed!!! We can only report our findings re oil...when an engine has been run on semi-synthetic we are finding very little wear after a season...when the engine has been run on fully synthetic we have found wear when we wouldn't expect it. I cannot see why you had problems with the newly bored holes for MGC followers as well as the original MGB holes. That is why I asked if you had a scraping device fitted. Have you fitted very strong valve springs? What cam profile have you run and what valve clearances have you used? I am trying to see if there is a pattern specific to your engine..... Peter |
| Peter Burgess |
| Hi, I am not using a crankshaft scraper (......I looks like I am using a cam scrapper......). The webs of the crank are edged and the conrods are also somewhat lighter (and polished to a certain degree). The only problem I can see with the bored holes for the C tappets is that the holes are maybe not in the correct offset position with the cam lobes. There has to be an offset between them, otherwise the tappets do not rotate??? However, it is very difficult to check this offset. One thing I observed is that the holes are rather large. I guess the clearance is 0.2 - 0.3 mm. That was the case for the B and C holes. I am using standard double valvesprings. The installed height is correct. All the cams were from Kent. The first a 714, the second a fast road cam from Brown and Gammons very similar to a 717, the last one a profile similar to a piper 270. Valve clearances were 0.4 mm (cold). Peter |
| Peter Brokke |
| Hi, There is another thing. I have alwsys found the valvetrain (tappets?) rather noisy. It was also irregular, sometimes the noise was there (tikking), sometimes it was less. This was from the beginning of operation. Peter |
| Peter Brokke |
| Hi The noise coming and going is characteristic of a worn camfollower...it gets loud when it rotates to a more worn part..( also shows your followers are rotating...at least on the worn lobes!!)...it might just be as you say ...you had a worn MGB block and the conversion to MGC follower has been given too much clearance. Peter |
| Peter Burgess |
| I designed most of Austin Rovers cams in the period 1985 -2000 including K series. The B series was a little before my time but I can remember examineing the calculations. The standard B series cam is a Multi sine wave design which was Austins own method devised by a great man Jack Bishop. There is an IMechE paper on the method if anyone is interested, also one by me on our later GCAM method. We really did lead the rest of the world by miles. All this methodalogy has fallen into the hands of Ford along with me curtosy of BMW. Ironically BMW's new V engine has probably still got a GCAM. To the question in hand, pitting is usually due to excesive contact stress ie the nose radius being too small and the spring loads being too high. The B series cam is hardened steel but the tappets are chilled cast iron a good combination from a tribology point of view. In fact this is the most commonly used combination in modern engines although its the other way round. Yes, as you increase lift the nose radius goes down and the eccentricity increases with the danger of running of the tappet. The B series cams are long period anyway so I would look elsewhere for performance increases. If Jack Bishop couldnt do it then it probably can't safley be done. I did a new cam for A series quite recently and ran into all of this. Before I sound too much of a smart ar*e, my B series has also knackered 3 of its tappets. |
| Paul Hollingworth |
| I am a victim of the Crane/Moss cam/lifter problem discussed by Doug Jackson on his British Automotive site mentioned by Clifton Gordon above. I shall post more about this at a later time when more of the dust has settled. Right now, however, I thought I would mention that the mechanic fixing my problem (for a variety of reasons a different one than the one who rebuilt the engine last year) is going to install lifters that have been "triple chill hardened" from England and apparently used in race Minis. |
| David Cushman |
| Peter, (Brokke) I agree with Mr. Burgess and think you have a clearance and/or alignment problem, .2-.3mm seems quite a lot. You may ask around to see if you can find a shop capable of sleeving the bores, or again going to an even larger lifter.. Paul, Excellent post! Sean |
| Sean Brown |
| Hi, I checked the clearance in the bore. It is very difficult to measure, but I think it is more in te region of 0.1 mm - 0.15 mm. I can also see that there is a clearly offset between the cam and the follower. I think Paul Hollingworth is making a point. The followers of the B en C engine were never designed for high(er) lift cams. That in combination with the poor quality of todays tappets almost must give problems. The solution is simple; find a good quality tappet. Why is that so difficult??? Peter |
| P.brokke |
| The following web site provides some good information about cams and lifters: http://www.webcaminc.com/ Click on cam Terminology. Clifton |
| Clifton Gordon |
| Regarding the hardened lifters I mentioned above, I emailed my mechanic, and the precise information is: The lifters are from Mini spares, their part Number, C-AEG580. they are in the London area. Their parts book says 3 heat treatments among other things. I would assume they would then have to cool them 3 times, but they do not say triple chilled lifters. |
| David Cushman |
| Really interesting stuff, this. Peter, I think there is an option which you have not considered - fit a standard camshaft. I quote Paul Hollingsworth in the message above "The B series cams are long period anyway so I would look elsewhere for performance increases. If Jack Bishop couldnt do it then it probably can't safley be done." When I bought my "Fast Road" head from Peter Burgess he recommended sticking with the standard camshaft. Seems like good advice to me. Mike |
| Mike Howlett |
| I had the same prob after 18000 miles on major rebuild. I consulted a shop that builds MG engines for vintage racing. He has the lifters rockwell tested for hardness, any thing less than 60 on the scale he throws away. About half the lifters he buys are too soft, these are the same lifters you and I are buying from the normal suppliers we do business with day in and day out,quality does not seem to mean much any more. By the way after he saves the best lifters he also drills them for better luberation. The cost on these are about eighty dollars a set. If it saves the cam and lifters its worth it to me BOB |
| Bob Swain |
| 'lo all... Has anyone ever gone nuts and drilled enough holes to feed hydraulic tappets in a B-series? I think of doing it every time I start my engine and have to wait for oil to get to the top end to stop the rattles :o) ttfn, -- Oliver Stephenson |
| Oliver Stephenson |
| For what it's worth - most of the engines I recondition come in with pitted cam followers and usually number three cylinder's inlet lobe on the cam badly worn. I am convinced that as well as the points made above, the longevity of the cam and followers is determined at initial start up and running in for the first 20 mins. I always run the engine at 2500 + rpm for 30 mins and whilst I rarely see my engines back again my own car's engine had done 150,000 miles and there was no pitting on the followers - just a circular even wear pattern. I only use 20/50 non synthetic oil, but also build the engines using Graphogen to generously lubricate the cam and followers - this graphite assembly lubricant also stays in the oil until the first change at 500 miles. |
| Chris |
| Hi Paul Interesting comments re MGB camshafts. Some years ago we were experimenting with a camshaft where the negative acceleration was too high and the follwer dug in to the nose of the camshaft lobe. I had an interesting chat with Bill Nicholson about the problem. He suggested tuftriding the cam would 'cure' the effects of the profile problem...apparently common practice in works racing circles where the performance envelope is being pushed to the max. We find MGBs respond very well to cam changes, especially in conjunction with an improved efficiency cylinder head. Cam and follower wear does not seem to be discerning as to profile. Billet cams wear the least, 'seriously' reprofiled cams that give even higher point loadings seem to wear fastest...especially with very heavy springs. The original camshafts also seem to be made to a very high quality..did Lydmet make the original cams? Re the 'K' series...tell us about the prototypes pushing out 140 bhp as a 1400 and 160 bhp as a 1600 for road use....how come the management detuned them when we understand the above figures were road driveable, well behaved and reliable? Peter |
| Peter Burgess |
This thread was discussed between 17/11/2001 and 23/11/2001
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