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MG MGB Technical - Changing Cam Bearings ?

Hi Guys,

Has anyone managed to successfully change the cam bearings on their block without sending it into a specialist engineering shop?
Is there a tool you can buy to do this?

I have three blocks that require the camshaft bearings changing.

Thanks in advance
Mark Hester

A special tool is required for this task. If the oil holes are not aligned properly, you're looking at a very expensive rebuild. The actual removal and installation of the bearings, with this tool, is a quick and inexpensive job. One of those projects better left to the machinist. RAY
rjm RAY

The special tool I use is an old camshaft cut off a inch behind the centre journal and the lobes turned off.

the two remaining journals are turned down for a third of their width so that they just fit inside the rear and middle bearings.

this can then be used with a large hammer to drive out the rear and centre bearings and drive in the new ones - the centre bearing is split and needs to be clamped on the tool using a worm drive clip.

a flat washer the size of the front bearing slips on the tool to drive out the front bearing and the new one can be driven in the same way,

I always use the prefinished bearings which do not need reaming in situ - minor scraping is sometimes needed, but generally they are a good fit without.
Chris at Octarine Services

I use the same type of homemade removal tool that Chris uses. Works like a charm! Prior to installing new camshaft bearings, check to be sure that a 30 degree lead-in chamfer is present on the faces of their mounting bosses inside of the engine block in order to prevent galling which will distort their Internal Diameter. When installing them, take care to assure that the oil feed holes are properly aligned. Also make sure that the rear bearing is properly aligned with the oil passage in the engine block that feeds oil to the rear rocker shaft pedestal, otherwise the rocker arm bushings will be starved of lubrication.

Avoid the camshaft bearings as sold by Moss, et al, as they are formed from a flat strip and rolled into shape. Consequently, they require that they be simultaneously reamed with a special factory tool after installation. Instead, use a set in which each bearing is manufactured as a single piece and requires minimal fitting. The best of this type are the Dura-Bond High Performance camshaft bearings (Dura-Bond Part # DA-2).

The Dura-Bond camshaft bimetal bearings are constructed from a seamless steel tube with a thin layer of Babbitt material. Their seamless construction makes for easy installation, eliminating breakage and bearing surface interruptions. These high performance camshaft bearings offer more than double the fatigue strength of conventional bearings, withstand increased valve spring loads better, while maintaining the excellent surface characteristics of Babbitt. Babbitt’s superior embedability, conformability, and anti-seizure characteristics reduce camshaft failures that harder bearing materials can cause. Babbitt material will deform under overload conditions, sacrificing itself rather than damaging an expensive crankshaft. A very thin layer of Micro-Babbitt lining reduces the microscopic deflections that occur in a heavily loaded bearing and thus increases fatigue life, making these bearings ideal for supporting a high lift camshaft at their higher operating speeds. Rapid cooling of the Babbitt during the casting process creates a very fine grain structure. By leaving the structure as cast, tensile strength is almost doubled over that of an Original Equipment bearing. The resulting hard and high strength condition provides the “toughness” needed for high performance applications. Micro-fissures that can lead to fatigue failure are eliminated by cold working of the surface during the burnishing process. Their tolerances are held closer in order to control installed oil clearances, which reduces their required minimum operating pressure. These camshaft bearings are available with a Fluoropolymer composite coating that actually penetrates the surface. The primary advantage is that bearings with this coating retain oil on their surfaces, even under extreme heat and pressure conditions. Being a lubricant itself, the coating provides back-up lubrication in the event that momentary oil starvation occurs. This characteristic is especially important during startup because oil does not reach all critical components immediately.

Should you elect to install Dura-Bond camshaft bearings, remember that under no circumstances should you attempt to hone the Internal Diameter of camshaft bearings, as the honing process will impregnate their surfaces with grit. A bearing diameter of .618” (15.6972mm) with an optimum Diametrical Clearance range of .003” to .004” (.0762mm to .1016mm) for high performance applications should be accomplished by reaming. Afterwards, the camshaft bearing journals should be polished to a surface finish of 10 microinches Ra in the same direction as that in which they rotate under service conditions. The journal diameters of an Original Equipment camshaft are- front: 1.789” +/- .00025” (45.4406mm +/- .00635mm), center: 1.729” +/- .00025” (43.9166mm +/- .00635mm), and rear: 1.623” +/- .00025” (41.2242mm +/- .00635mm). The endplay (endfloat) of the installed camshaft should be .004” +/- .002” (1016mm +/- .0508mm).
Stephen Strange

Thanks for your input guys.

If you can't readily purchase a tool then I guess this is a machine shop task.

I here what you say Steve about the cheaper Moss bearings.

An mga twin cam Jack Shaft or half speed will run in the cam shaft hole, so the load on the bearings won't be as great but the bearing tolerance needs to be precise to get the backlash correct for the main timing gears.

Mark Hester

This thread was discussed between 30/07/2010 and 01/08/2010

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