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MG MGB Technical - Cam damage
|I removed the engine from the 1970 B I purchased a year ago in order to repair oil leaks and to install an overdrive transmission. Although timing cover and rear main seals were the suspected culprits, the leaks were from the timing cover gasket due to loose and missing bolts and at the rear, to a bad transmission input gear seal and to a leaking oil pressure gauge hose. The previous owner indicated that the engine had recently been rebuilt.|
This car has always had a rough idle. The carbs have been completely rebuilt, pertronix fitted and new engine valves installed. Compression is 127 PSI straight across.
Suspecting that the idle might be rough due to cam damage, we pulled the lifters and found that three out of eight lifters are badly pitted. The other 5 lifters were pristine, with a mild circular pattern demonstrating that they have been rotating properly. I am therefore replacing the cam with a stock unit. Are the uprated "short" lifters indicated to replace the taller vented lifters that were stock in the engine? Would the rough idle be due to a rounded out cam?
A few months after "SL" oil was released, my "A" Series midget started to lose power. When the engine was disassembled, all was in order except for the cam and lifters. All 8 cam lobes were rounded and the lifters were all badly pitted. Use of oil with high ZDDP content has kept the A healthy since. I assume that the previous owner of the B may not have been aware of the need to use specially formulated engine oil. The question is, why would some of the lifters be in perfect condition while the others were so badly worn? Would this be due to oil, improper engine lube at assembly or fate?
|Poor lifter material. As I remember, there were issues with these some years back.|
|Bruce TD4139 Cunha|
|Glenn: since you are going to replace the cam, go ahead and get a performance cam. You can have best of both worlds.|
Rough idle in my 79 B was found to be intake/exhaust manifold nuts had loosened and created a severe vacuum leak. Check the nuts that fasten the carburetors to the manifold also.
|Glenn, when a new cam/lifters are installed a special cam oil (more glutinous, looking at the oil with my Kent cam kit)is recommended, as on initial start up the new/freshly installed cam is starved of oil. Maybe this was the issue? The short lifters (cam followers in Blighty) should, I think, have been standard by 1970. As I understand it, these were stronger and lighter and borrowed from the Mini Cooper.|
|P A Allen|
As well as using a cam oil on ALL the contact faces when assembling. Make sure that the clearances are set according to the cam manufacturers specification, which may be different to standard. Also and this is important; run the cam in for 15 to 20 minutes at 1500 to 2000 rpm not letting it idle. If you have to make adjustments switching off and re-starting is OK. Low revs put greater pressure on the follower/cam interface. Cam suppliers usually recommend using a ZDDP additive as well, but always use a "Classic oil" which has a decent ZDDP content.
As PAA mentioned the later "SHORT" followers superseded the longer variety. I think with the arrival of 18V. The push rods were also longer.
|A pal bought a fully restored including engine MGB from a local garage, and had them maintain it for him. 20k miles later it was running very poorly and the cause was found to be badly worn cam and pitted followers. The oil they had always used was SL, and they neither knew about or seemed interested in ZDDP issues. Since having the cam and followers replaced he has used SE. Could be oil, could be poor quality cam and followers, could be poor rebuild technique. But since replacing the cam and hydraulic followers in my V8 I've done over 30k on SF and SJ, and am not aware of any problems. I didn't use a cam lubricant, although I did put a drill on the oil pump immediately before the first start to ensure oil at normal working pressure got everywhere, and I did run it at 1500-2000rpm for some minutes. |
More and more oils of suitable viscosity for our engines have had their phosphorus and zinc content reduced in the last few years, changing to SL from SJ which is becoming harder to find, including those suitable for Diesel engines as well as petrol (Diesel engine requiring more protection).
|Gary, Do you have a particular performance cam that you recommend? I would prefer to sacrifice some performance for a smooth idle. I have an A/C unit adapted to the car so at idle in the heat things tend to get a bit rough anyway.|
I have been using a specialty oil from a small blender in the Midwest, Central Petroleum Company. The owner specializes in oils for old farm equipment and as a British car owner himself, has a racing oil that is blended with approximately twice the ZDDP that came in SE. I have been using their straight 30w for about 5 years in the Midget with no problems. I suspect that the PDO of the B was using something off the shelf, no doubt SM.
|Glenn, the camshaft, in a flat tappet engine, receives the most wear of any internal engine component. The surface pressures are extremely high and without the proper lubricant, the camshaft will indeed be short lived. When I put together my spare 18GB engine, back in '93, I used the later short lifters and long pushrods. I installed a Kent 285 camshaft that has been proven to be an excellent choice. It delivers a smooth idle as well as increased power. I've owned my '67 B since '72 and have always used Castrol 20W50 oil. Whenever I go to adjust my valve clearance, I'm amazed that very few of them need any attention at all. Nowadays, with the constant changing of ZDDP levels in the oils on the market, I use Castrol 4T 20w50. It's designed for 4 cycle motorcycle engines and has a higher detergent package than regular oils. It even gives me an extra 5 psi of oil pressure across the board. RAY|
|I went with an APT VP12 Cam for my 67 GT rebuild. Idle is a bit higher (1100) but smooth, and the power increase is nice.|
|Bruce TD4139 Cunha|
|Glenn: My cam was spent at 97k. Former PO's had abused the engine. I went with a Crane 270. I get a smooth idle, good "pull" in the 2500-4000 range. |
Car is running fine with 127k on it.
|I am amazed at how smoothly the Piper HR270 idles in my car. It pulls really strongly at low revs as well. You can get them from Peter Burgess. It replaced a reground Oselli that was worn to about 1/3 of its nominal lift after 30k miles. I posted a link to some pictures including cam followers looking like the surface of the moon. 1000 ppm of ZDDP for my car now.|
I have some dashcam footage I can email you a link to if you want.
This thread was discussed between 20/02/2016 and 27/02/2016
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