One ConRod Different - Should it matter?

[Sam_Finlay]

Advice required - Bought a scrap, seized, 1098 Midget Engine last year to rebuild as a spare. ( The engine number plate is missing ) Stripped it down & freed it up last night / this morning. Been inspecting & cleaning the parts prior to replacement if required before the rebuild.

It was seized on the third pot with all the pistons at TDC. A couple of the bores are stained but I can't see or feel any significant pitting other that maybe a little bit in one area where the rings had fused to the liner in cylinder three. The block has been rebored +20 in the past but all the white metal bearings look fairly clean and unworn with only very minor scoring in the odd place.

The ConRod that came out of pot three is marked - MOWOG 12G 127 A 51, has thinner bolt heads at the big end bearing and just looks lighter & newer than the other three that are marked - MOWOG 12G 124 A 8. All the rings are fused on pot three but free on all the others.

Big Question. Should I just glaze bust the bores, stick a new set of +20 rings on them all, put it all back together and hope for the best OR replace all the ConRods, Pistons & Rings and have it rebored to +30?. The main bearings also look OK but ??????

The later option sounds potentially a tad expensive. Thanks

[bmcecosse]

You should have 2 X 12G 124 rods, and 2 X 12G 127 rods in the engine. Check again.....

[Sam_Finlay]

- Should have checked all 4 rather than just looking at the ones either side of the lighter coloured one in the photos.

So I might as well just stick a new set of piston rings on, clean it all back up and put it together. - Thanks[frame][/frame][frame][/frame]

[MarkyB]

The one with the seized rings needs special attention, it looks different, and the rings seized.
Is the oil-way up the rod clear?
Any sign of cross hatching on the bores?

Actually the crankshaft journals look a bit odd, the one on the left looks fine as do the mains, the middle two look a bit unbalanced.

[bmcecosse]

The big-end shells are knackered - can't see the mains shells - but the journals look quite marked. An exchange crank from Bull Motif is an amazing bargain - be sure to fit a new oil pump too. You must get any sticky rings off - and check if the piston lands have been damaged.

[chrisryder]

an exchange crank may not fit as the OP said it's a 1098 midget engine, not minor. so the mains will be bigger on the midget engine.

[bmcecosse]

Not with these con rods !

[chrisryder]

does the big mained midget 1098 have different conrods too then?

[chrisryder]

these are the rods that came out of my big mained 1098, but they don't look standard to me!
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[bmcecosse]

Hmmm - these just look polished up - I was expecting 'big mains' 1098 Spridgets to have Cooper S type con rods (well, AEG 625 rods anyway) but I guess not if these definitely came from a big mains block . So the earlier comment re exchange crank maybe not fitting does indeed need checking out !! Of course - only the later 1098 Spridgets had the big mains block/crank combo.

[Sam_Finlay]

Sorry - been in the garage cleaning up the block and trying to free the fused piston rings etc. this evening. No luck so have left to pickle overnight.

I am guessing that it's an OLD 1098 midget engine based purely on how rusty everything is but no idea really. The block is marked - MOWOG 4 with 207 ( vertically at 90 degrees to this ) and 12G 432 ( offset to the right ).

Yes, the journals are marked but I didn't think they were that bad as I can't feel any lips anywhere but I'm no engineer. Hence the request for advice. As for the bores - well they are stained & I can feel the odd bit of pitting where the rings were fused. I was hoping to get away with just scouring it and fitting the new rings but can see that it could be a false economy now that I've seen what a full gasket set is going to cost.

Based on the comments this evening then should I be leaning back in the direction of a crank regrind, a rebore and a new set of shells all round? If so, any recommendations for a local Midget specialist in the South West?

[MarkyB]

My comment about the journals was about the dark line around the middle where the oil feed emerges.
It appears to be missing or offset on 2 and 3 which makes me wonder how accurately the crank was ground.

Any engine reconditioner should be able to check it, for the price of a beer if you are lucky.

[Sam_Finlay]

Thanks MarkyB, but all of this may be a bit academic now. I have found what feels like a vertical crack in one of the liners. Its not a score mark. Starts more than half way down and ends at the top of the bore. Might explain why it was scrapped.

I'll have the grinding guy look at the crank and the block and give me an opinion before I do anything else as you suggest. As a side note it has been interesting to see how much more expensive 1098 Midget parts are compared to 1098 Morris parts from specialist suppliers servicing each. There's a +£40 difference for a set of MG pistons and rings.

[bmcecosse]

There may be a good reason for that price difference...... If the liner is cracked (IS the block linered? Not common on 1098 engines) then indeed it's probably just scrap. The crank regrind price will be FAR more than the exchange crank from Bull Motif. If nothing else - save the camshaft - it's a v good upgrade for a 948 engine!

[chrisryder]

i believe you could save the crank, if the mains are 2 inch diameter, and if not badly worn, it can be used for 'stroking' a 1275 engine. but other things would be required to get the piston crown to deck height correct.

[Sam_Finlay]

I really should be working.

The mains are 50.78mm ( Cheap Vernier ) and the bores are about 64.52 'ish mm. Which means not a lot to me other than yes 2" mains but you lost me with the "stroking" reference.
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[chrisryder]

the 'stroke', which is the difference in piston height from TDC to BDC is governed by the offset of the centrelines of opposing big end journals. alternatively it's double the distance between a big end journal centreline, and a main journal centreline.

1098's have a longer stroke than 1275's. effectively the 1098 has a 'wider' crank if you lay the two down next to each other. you can increase the stroke of a 1275, and therefore increase its capacity, by fitting a 1098 crank. you can't normally do this with a normal 1098 crank as they don't have the same main journal diameter, so it'd flap about a bit in a 1275. with a big mained 1098, you can fit that crank in a 1275 block as the mains are the same size.

the only problem with that is that the crank then pushes your pistons further up the block, and then the crown of the piston would pop up from the deck face of the block! your head wouldn't last long which is why you'd need to remedy that if you were planning on doing that. i presume, as all conrods are roughly the same length, you would have to get pistons with the right gudgeon pin to crown offset. you will notice that 948 pistons have their gudgeon pins quite a way down from the crown compared to 1098 pistons, this is to overcome the shorter stroke of the 948 and make sure the piston gets all the way up to the top!

i hope that makes sense!

[Sam_Finlay]

Yes that makes perfect sense Chris.
So how rare are liners in a 1098 then Bmcecosse? Worth relining if such were findable?

Cleaned the head up last night and was amazed at the amount of white crud baked onto and around the exhaust valves.Would that be from using unleaded petrol as all I had expected to see was black carbon deposits?

[bmcecosse]

Well! It certainly IS a 2" mains block (and crank) so WELL worth doing all you can to salvage it!

[Sam_Finlay]

Good news. The experts ( I hope ) recon it's unlikely that the liner is cracked, just scored, but don't recommend taking out to more than +30 from its original bore. So a +10 hone is a possibility but I will need to source a set of +30 pistons and rings. I'm looking at what that'll cost before I do anything else. Would 1098 Mini ones do the job?

The crank would benefit from "a polish" but should I go for a full regrind? Oh! - And I've bought David Vizard's very thick book as a bedtime read.