MA-U-H 180898 engine

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Clampit
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MA-U-H 180898 engine

Post by Clampit »

I have a spare engine and the id plate says 10 MA-U-H 180898. I understand this is a high compression engine. The markings on the piston tops are m2007 mowog N38 and both the pistons and block are marked 2 (Assume means standard size)
The head has 23453 12G202 MOWOG and the number 4 and letter B written on the top across the rocker area.
Can anyone tell me please, is it the block and head that make it High Compression or just the Head ? Also, do you use the standard available head gasket for this engine. Thanks and best regards.
philthehill
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Re: MA-U-H 180898 engine

Post by philthehill »

The pistons make for high or low compression and is determined by the amount of dish in the top of the pistons.
High and low compressions 1098cc Minor engines have the same height blocks and in fact are the same in every detail.

The 2 on the block and pistons indicate the sizing of the bore and pistons.
Even with the best of intentions the bores may not be the same diameter on all four cylinders - so selective piston sizing is used.
You can have 1, 2 or 3 graded pistons fitted to the same block.
If they are the same it was bored on a good day. :D

The 12G202 cylinder head is a standard 1098cc Minor cylinder head.

A standard 1098cc cylinder head gasket will suffice.
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Clampit
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Re: MA-U-H 180898 engine

Post by Clampit »

That was helpful thank you, they all have the same “2” marked on each piston and there is little sign of wear but the head shows a lot of wear in that three of the rockers have probably 3-4mm side movement that suggests its done a few miles. The block is painted Gold while the head is, well no colour really. This is the reason for my question “what makes it high compression” Anyway that is what I wanted to know thanks.
philthehill
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Re: MA-U-H 180898 engine

Post by philthehill »

When you say that the rockers have 3 - 4 mm side movement do you mean that they rock on the rocker shaft by that amount or do they slide sideways on the rocker shaft by that amount?
The rockers in good condition should not rock on the rocker shaft but they can slide sideways by that amount.
You will most likely find that the rocker shaft is worn out and needs replacing. It is very rare for the rocker bushes to wear out which is a blessing in that you can reuse the rockers. Pressed steel rockers should not be re-bushed.
It should be noted that the oil feed to the rocker shaft and locating peg is on No: 1 rocker shaft pillar. With later shafts - No: 1 rocker shaft pillar with locating peg is moved to No 2 position and No: 2 pillar is moved to No: 1 position and may need to be drilled to allow the oil to flow from the head to the rocker shaft through the new No: 1 pillar. See drilling picture below extracted from the Vizard book Tuning the 'A' Series.
The hole in the foot of the drilled pillar needs to be countersunk to ensure that the hole in the head and rocker pillar are not obstructing one another.
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Clampit
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Re: MA-U-H 180898 engine

Post by Clampit »

I will study this thank you. Out of eight rockers four rock on the rocker, the others seem ok. The rocker shaft is probably worn out so I will take it apart to see what’s going on. :lol: I will also take a look at the valves and guides and decide what to do now I know it’s a normal 1098 head. Well done & thanks.
David W.
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Re: MA-U-H 180898 engine

Post by David W. »

Phil
When you say the pressed rockers should not be re-bushed, were they bushed originally?
I've noticed that my pressed rockers are bushed, but that the oil hole doesn't line up with the hole in the shaft.
20180605_102429.jpg
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The yellow markers show the oil holes in the shaft, and the white marker shows the location of the hole in the bush. The location is the same on all 8 rockers.
David
philthehill
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Re: MA-U-H 180898 engine

Post by philthehill »

The pressed steel rockers do have a bush but factory fitted.
If the bush is replaced without the correct equipment there is a good chance of the rocker distorting and being made useless.
It is rare that pressed steel rockers need to be re-bushed if at all - the rocker shaft wears out but the bush wears very little.
The hammer tip is where the main wear takes place and if the wear passes through the case hardening the rocker is scrap.
As you can see in the picture above the rocker is made up of a wrap round piece of steel spot welded together coming together at the hammer.
The oilway that is indicated by the white tie wrap goes up between the wrap round plate to the adjuster screw and allows oil through the hollow centre of the adjuster screw to the ball and then down the push rod to the cam follower and back to the sump .
The hollow adjuster screw was latterly ditched by BMC for the solid screw with no oil way but the oilway in the rocker was retained but made redundant.
If you have hollow waisted adjuster screws they should be replaced with solid non hollow waisted screws. There are several types of adjuster screw so make sure that the correct ones are obtained.
The important thing is that oil is getting along the rocker shaft and out of the shaft to the rocker bush.
There was also originally a top oilway in the rocker but when blocked keeps oil away from the valve stem.
The small 'O' ring valve stem seals are next to useless - the top hat seals with the correct valve guides are best.
BMC originally fitted a shroud over the spring to keep the oil way from the valve stem but it was found to be ineffective and was soon discarded.
Phil

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