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MG Midget and Sprite Technical - 1275: Front cam bearing position.

Is the position of the front camshaft bearing correct?

Or should it have been installed flush with the face of the block?




Lawrence Slater

Here's another, looking up at the bearing from below.

Lawrence Slater

it needs to be positioned so the oil feed holes match up; from the 1st pic it looks as if it was flush with the block then the oil feed would be covered
David Smith

Hi David,

Yes I agree, it couldn't be moved forward any more because of the oil feed.

However when the cam bearings were fitted the front bearing was even further back, and the guy that fitted them, told me the oil feed should be in the center of the oil slot in the bearing.

But that meant that the front cam journal was only running in a portion of the bearing, and the back of the bearing was substantially covering the cam follower hole.

I moved the front bearing forward to it's position in the picture. But that still leaves a portion of the cam journal running in air.

I always wondered if this was the wrong cam bearing, meaning that it had to be fitted this way, in order to get the block oil hole, and cam bearing oil slot to line up.

What's the point of the full width of the cam journal and cam bearing bearing, if neither are in contact over the whole of their surfaces?

I've never seen an original factory installed cam bearing and cant find a picture of one.

I'm stripping this (spare) engine for a rebuild, and want to ensure this is right.
Lawrence Slater

I put cam bearings in my engine only recently and you should be able to centralise the journal and get both holes lined up. The journal will run on the entire bearing if it's installed correctly. Two holes in block and two in the bearing. If I remember correctly the holes are not central in the bearing so you may need to flip it over to get it right.

I remember having to think about it and measuring the hole positions to get it right. I think the bearing hole may go where you have the slotted hole because the hole is further back to match the block. Can't be sure though.

Greg H

Hi Greg, is that two different types of bearing set for a 1275 engine?

Anyway, That's what I thought. The bearings should be lined up with the oil holes, and centralised too. But I couldn't do that because the oil slot is central on the bearing rather than offset.

That's why I wondered if the correct bearings were installed in mine. (At least the front one anyway)

I can't tell from your pics if the oil slot is offset, but from what you say from memory they must have been.

The pics I posted, are from the engine before I installed it over 20 or so years ago, at least.

There is a background reason I ask about this.

It ran for many many miles before being swapped out, and currently is siting around awaiting a strip down.

There doesn't seem to have been any untoward effect from the bearings as installed in the picture, other than the one I describe below. -- Possibly--. And this is why I want to know exactly how the cam bearings should be installed.

Others have had sump oil sucked up through the timing cover, and into the carbs, via the crankcase vent pipe. I had exactly this problem myself, and could never work out why.

Prior to the engine rebuild with the bearings shown in my pics, I didn't have this problem. Then new cam bearings fitted, engine installed, and I am sucking oil into the carbs, when the oil is just getting warm.

It was never resolved, and I swapped engines for my current engine.

But I always wondered if the root cause of the oil being sucked into the carbs on my now spare engine, might have been that too much oil was allowed to get into the timing cover (which couldn't drain the excess fast enough), because the front journal of the cam shaft, wasn't covered fully by the cam bearing.

Did this cause excess oil, to squirt into the timing cover, and hence get sucked into the carbs, until the oil was hot(thin) enough, to drain fast enough from the timing cover and back into the sump?

It will also be interesting to see the wear pattern on the front journal and bearing.
Lawrence Slater

Not my bearings just got the pic off the net. My bearings are in my engine but the bearings in the pic are exactly the same as mine. i.e. a slot and a hole. The round hole is offset and the slot is central. Check one way and if it doesn't look correct flip bearing over so the bearing holes will go to the opossite holes in the block. So there's two ways it can go in.I think I put my bearing just as crap back from fluch at the front and the holes still lined up.

I'm not sure about whether less bearing under the journal would let more oil out the front into the timing cover. I think the oil flow through to the timing cover would be soley dependant on the clerance (size of the hole) and not how long it was i.e. how much overlap. Could be wrong though.

Here's one to think about for a smokey engine.... Soon after buying my car many years ago I rebuilt the engine and I just honed it. Looked ok. It was already +0.060 and had been rebuilt before I owned the car. After I rebuilt it I always thought it was just a tad smokey for a new engine. So rebuiling it this time I took no chances and sleeved it back to standard and spent quite a bit of money on it. Now after I had done all the machine work a mini expert looked at my dipstick tube and told me it was upside down. I thought no it couldn't be because that's how it was when I got the car. I check here on the forum and everyone confirmed it was. The way it was installed the long narrow bit was out the top and the flare in the sump. This resulted in the top of the tube being nearly 30mm (1 1/8" for the yanks) higher and so an extra 1.3L of oil went into the engine to get full on the dipstick. The ring gap was just out of spec but I do wonder if all I really needed to do was put the dipstick in the correct way.
Greg H

Well if what you say is correct, and I have no reason to doubt you, then I have a dodgy front bearing in my engine then.

Is the widest bearing the front bearing?

If so, then my front bearing only has one oil hole (slot), whereas the ones in the pic you posted have two.

If that's the case, that's why mine are installed the way they are; wrongly

Small mistakes can have odd consequences that's for certain.
Lawrence Slater

Yes widest one to the front. The load is at the front so it has the wider bearing surface.

The oil comes form the main bearing through the bottom hole to the cam then out the other hole and up to the rocker gear. If the front cam bearing has only one hole then how is the oil getting up to the top of the engine to lubricate the rockers?

You had me doubting myself and so I checked my Vizard book and the oil flow is in there, page 400.

Maybe there are variations in blocks and oil flows? Surely someone else has some knowledge of this?

Perhasps the oil flow to the cam is set up so there's enough pressure to pump it up to the top of the engine but if it can't the extra oil goes out the front into the timing cover.

How did the rocker gear look?
Greg H

Hi greg,

Looking at the 2 pics I posted I can't see a hole going up to the rockers.

The rocker shaft is a bit knackered to say the least, looks starved og oil (I assumed it was blocked with gunk and muck), but there was plenty of oil floating around up there whenever I did the tappet adjustment.

So there must be oil getting there from somewhere, and if the only place it comes from is the cam bearing, there must be a hole, --- perhaps out of sight in the pictures I took.

Do you see the notch in the front of the cam bearing, in the picture I labled as "Here's another, looking up at the bearing from below"?

If there is supposed to be an oil hole, I can't see it, but perhaps it's just out of sight in the angle I took the pics.

I also dont see what that notch is doing and it doesn't appear in your pics.

I'll be sure to look when I strip the engine down.
Lawrence Slater

Lawrence

In Greg's photo, the set nearest the camera all appear to have the notch in them.

The small (rear) bearing seems shorter than the corresponding bearing in the other set, though.
Dave O'Neill 2

Hi David O.

Yes I see the notches now, --- on looking properly.:)

On the front bearing, the slotted oil hole appears to be 180 degress to the notch, and the round hole between them at something like 90 degrees or less from the slot.

If so, then mine could be just out of sight of camera view I guess.

I don't remember the hole. I shifted the bearing as far forward as I could, and still keep the oil hole uncovered by the slot. I'm sure I wouldn't have covered an oil hole if there had been another visible.

Well the only way I am going to know for sure, is to get the bottom and front of the engine apart. That's a job for the end of the summer though, as I've other things to do now.

This is probably not attracting much interest. Otherwise I am sure there must be somebody out there that has the definitive answer to EXACTLY how the front bearing is installed, and if mine were installed correctly or not.

What is needed is a factory drawing or photo, or pic of an original installation.

Thanks for those replies anyway.

Lawrence Slater

And what does the notch do anyway?
Lawrence Slater

Lawrence,

As a number of the bearings shown earlier appear to have some form of notch a guess would be that they are to aid alignment when placing them in the block with a production tool.
David Billington

Ah yes thanks David B. That makes perfect sense.

So notch is likely irrelevant as far as cam installed position is concerned. Any maybe mine are installed properly anyway.

But my feeling is that they are wrong.

Why would the bearing have been designed to sit recessed from the front face of the block, and protrude into the interior of the block, so that the journal of the cam is not wholly within with the cam bearing?

The bearing and the journal, are both the same width, so they must have been designed to have been lined up when installed.

Or maybe not?

Does anybody know if there are design drawings for the cam and bearings on the web anywhere, or anywhere for that matter?

Lot of Davids on here :)
Lawrence Slater

I do know EXACTLY how they are installed but no idea why you've had problems. When your engine is apart and you have a new set of bearings in hand I'm sure it'll all be self explanatory.

The notch on the small bearing (the rear) is how the rear bearing gets its oil. There is a pin hole on the back of the oil pump. Oils sprays out of the pump goes around a gallery in the back of the pump until it gets to the notch then goes into the cam bearing.

I believe the notch on the front bearing is used to get oil onto the cam sprocket. Remember the triangle camshaft retaining plate? It has a hole in it. It can go on three ways but only one way is correct otherwise the oil that sprays out the front cam bearing won't get out through the hole to the sprocket.

The first set of pics where mini auto and manual bearings which I think are different.

Greg H

Hi Greg,

Thanks for explanation of the notches.

Whoops. When I used the word EXACTLY in my previous post, I didn't explain that very well. :)

What I meant was, in exactly what position the front bearing should sit. I should of said where, and not how. I've found loads of references to how to install them, even on a DIY basis with cut down camshafts as a drift. But I can't find a reference to positioning. Perhaps it's just so obvious that it needs no explanation.

Anyway. You've given me enough info I reckon to see how it should be, when I take it apart.

The memory plays tricks over the course of time, but I just don't remember seeing that other round hole in my front bearing. However, as you said the oil has to get up to the top somehow, and there was definitely oil up there. So logically if there is only one oil path, the hole must be there.


Lawrence Slater

EXACTLY understood :)

Yes aligning the holes is fairly obvious but I was stumped on the rear for a little while because there was nothing stating where the notch should go. I later realised it didn't really matter as long as the slot was at the back and aligned with the gallery but when there is no clear statement you keep looking for something to be sure.

If there's oil up top the holes must be lined up but I suspect still in back to front which is why to line the holes up it had to be further back. Next time try both ways and I'm sure the correct way will be clear. I know because I almost made this mistake.

One job where if you haven't got the right tools it's not a lot of fun! I used a long threaded rod, straight through from front to back. With a piece of wood say 6" long on each end. Bearing under wood then by tightening up the nuts was able to pull them in but you really need something to stop them skewing. If they go crooked it doesn't work but once you get the first 1/4" in square they go in ok. Was quite a bit of stuffing about to get it done.

I would have normally got the machine shop to do it but had already picked up my block when I later decided to do them. It would have been a bit of a hassle to take it back. Plus I'm a tight ar*e and saved a few dollars. If your block is going to the machine shop it may be easier to just give them a few pounds. I enjoy building engines but this is one bit where if you haven't got the tools it can be a bugger of a job.
Greg H

Hi Greg,

Thanks for the tip using wood. I did wonder about doing myself some way.

My pics were of the bearings fitted at a machine shop. Well actually, after I moved the bearing toward the front face of the block, as I thought they were wrong.

That's partly why I want to know the details, so that when I get them done again, or do it myself, I want know how they should be.

But I reckon I will get a shop to do them, from what I hear it's pretty cheap still, and quite a bit easier than trying myself.

On the other hand, I too like to save money :):):):), and also like the challenge.

Cheers

Lawrence Slater

This thread was discussed between 02/08/2011 and 05/08/2011

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