Building up a spare 1098

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Building up a spare 1098

Postby Monty-4 » Fri Sep 16, 2016 5:05 pm

Hi folks.

I'm going to be rebuilding a spare 1098 I'm picking up over the next few months to swap in as mine is a little tired.

The aim is to build something as torquey (high gearing) and reliable as possible. Are there any mods (e. g. centre main strap) or parts purchasable in higher grades to this end other than sourcing the block with larger mains (10CC)?

As documented on this forum I have the 12G940 head, HIF38 and 1.5" exhaust "bmc/Roy" style setup. :)

Thanks for any input.
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Re: Building up a spare 1098

Postby Panky » Fri Sep 16, 2016 6:06 pm

They're the mods I've done and they do make a nice difference :) I've currently got a Mini combined manifold to take the 1 1/2" carb but will soon be swapping that for an alloy inlet and Midget exhaust manifold - I'll let you know how I get on.
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Re: Building up a spare 1098

Postby Monty-4 » Fri Sep 16, 2016 6:42 pm

Centre main strap too?

Are there higher quality thrust washers, mains or piston sets available that'd put my mind at ease for 100,000 miles? Turbo pistons maybe? :)
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Re: Building up a spare 1098

Postby Panky » Fri Sep 16, 2016 7:09 pm

100,000 miles of trouble fee motoring? Better fit a Japanese engine ;)
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Re: Building up a spare 1098

Postby Monty-4 » Tue Sep 20, 2016 2:35 pm

Hah! Point taken.

I'll be going pretty standard then. Trying to avoid getting tempted by +0.60" bore and aftermarket cams.
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Re: Building up a spare 1098

Postby The vast minority » Tue Sep 20, 2016 2:50 pm

I own that car of BMC's now and before I did, my mate did.
On several trips round the Yorkshire sales, he could never leave me on any incline when flooring the pedal in the car, I stayed with him easily in my standard 1098.

Thus, I wonder if the mods do anything other than decrease MPG, the traveller was always worse on these joint runs than was Kermit the Mog in this department.

My observations for what they may be worth.

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Re: Building up a spare 1098

Postby Panky » Tue Sep 20, 2016 5:08 pm

That's the 3.7 diff on the modded engine, with a 4.2 he would have left you for dead on he hills. I've found fitting the 3.7, along with all the 'Roy' mods dulls the acceleration back down to where a standard engine with a 4.2 would be - but you get a more relaxed cruising at high speeds.
I've just removed the combined Mini manifold and fitted a Midget exhaust manifold and a Minisport alloy inlet, not tried it yet 'cos it won't start - no spark :roll: But when I do I'll report back.
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Re: Building up a spare 1098

Postby Monty-4 » Sat Oct 01, 2016 6:45 pm

Right. Getting to business now.

I've got a second block, a great standard crank (no visible scoring although yet to run my nail over it), a cam that also looks fine to my eye and an oil strainer assembly for a grand total of £30. My budget short-block build may be feasible. Now if I can pick up some con-rods and a flywheel cheap...

For the head, I plan to teach myself to port a 12G202 or CAM4810 from the yellow bible. Of course this will take me years so I'll swap over the 12G940 when the bottom is done.
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Re: Building up a spare 1098

Postby Monty-4 » Tue Oct 18, 2016 10:11 am

Got a set of cheap con-rods. My chosen machine shop - who apparently have a lot of experience with Mini engines - will tell me if they're junk, I suppose.

Now for pistons. I've been looking around and the options for 1098 seem to be standard 6.9cc dish or (mightily expensive) flat-tops. Would the 3cc dish 1098 pistons from a Sprite work?
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Re: Building up a spare 1098

Postby woodywoodchipper » Tue Oct 18, 2016 5:43 pm

yes, same block,
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Re: Building up a spare 1098

Postby Monty-4 » Wed Oct 19, 2016 2:40 pm

Maths.

6.9cc dish = 9.3:1 static CR.
3cc dish = 10:1 static CR
Flat-tops = 11:1 static CR.

+/- about 5% depending on overbore. E.g. 9:89 to 10:31 with 3cc dish from +0 to +60 thou.

I imagine 11:1 would be completely nuts?
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Re: Building up a spare 1098

Postby Panky » Wed Oct 19, 2016 3:48 pm

I'm told that the weak point on the 1098 is the crank so I wouldn,t go too mad with the CR
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