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1098 Engine Project - Take 2 - Big Bore/Short Stroke
https://ausmini.com/forums/viewtopic.php?f=5&t=99579		 Page 1 of 4
Author:  timmy201 [ Sun Jan 05, 2020 7:48 pm ]
Post subject:  1098 Engine Project - Take 2 - Big Bore/Short Stroke
Time to plan and scheme for the next project!

The previous 1098 engine & gearbox project is now running and driving really nicely. It took me about 5 years from start to finish as I took my time collecting parts and getting all the work done.
viewtopic.php?f=5&t=85524

So, this time is something completely different... The normal Aussie 1098 engine is a long stroke (83.8mm) and small bore (64.6mm) engine, and shares the engine block with the 998. The long stroke engines traditionally have better bottom end power and less top end power, and small bore engines can limit the size of the valves that you can fit. They also have a higher piston speed due to the distance they have to move each revolution

What I've planned for the next engine is a short stroke (68.4mm) and big bore (70.6mm) engine. This configuration was used on the 1071 Cooper S to compete in the 1100cc class. Later on in South Africa they made short stroke crankshafts so that they could make both 1100cc and 1275cc engines from the same engine block. I'd heard of a few guys in the UK turning these into fun little engines, and it sounded like something I'd like..

So the starting point:
1100S Auto block - standard bore
12G940 head - standard 9 stud
12G2827 crankshaft - standard/standard grind (2.0" main and 1.75" big end)
1100S standard rods and pistons

So this engine will be built up as a high rpm revving engine. I think the block has all the modifications done to convert to a manual gearbox, the head will need a service at a minimum and I'll consider getting some bigger valves installed. The crank will need to get ground to at least 010 undersize but they are considered one of the strongest cranks available due to the large journals and overlap between the main and big end bearings. The rods have the heavy caps on them, so will need to be lightened at a minimum before I use them.

I've still got lots of decisions to make regarding the final spec, and this will take another few years to get the parts for and the machining work done. I'll have to add in a disc brake kit before I get this done too

Attachment:
130EA2DE-6AC2-4EE8-B2BE-DDA08113FD15.jpeg


And why not just do a 1275 engine? I guess just because I can and want to do something different :D
Author:  braad [ Sun Jan 05, 2020 11:09 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
This sounds interesting! I’ve never heard of someone doing this with a 1275 before


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Author:  9YaTaH [ Mon Jan 06, 2020 7:30 am ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
Nearly square...so should spin like a top :!: :D
Author:  TK [ Mon Jan 06, 2020 10:46 am ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
Tim,
I have a few South African cranks in the shed and I will be doing a similar build to you. I will be using Innocenti rods though just for strength and lightness.

EDIT: Vizard confirms in one of his books that the A series is most efficient with a small stroke.
Author:  timmy201 [ Mon Jan 06, 2020 8:11 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
braad wrote:
This sounds interesting! I’ve never heard of someone doing this with a 1275 before


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I haven’t actually heard of anyone running one here in Australia. If anyone has done it here I’d love to hear about it
9YaTaH wrote:
Nearly square...so should spin like a top :!: :D

Yep, this one will be an undersquare engine which is the opposite to most A Series engines.
TK wrote:
Tim,
I have a few South African cranks in the shed and I will be doing a similar build to you. I will be using Innocenti rods though just for strength and lightness.

EDIT: Vizard confirms in one of his books that the A series is most efficient with a small stroke.

I’m still deciding on how to sort out the rods. It’ll definitely be interesting to see how it performs once it’s done, hopefully nice and smooth and revvy :D
Author:  jpodge [ Fri Jan 10, 2020 8:12 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
Sounds like a cool project there Timmy and I am sure we will enjoy reading this thread just as much as we did with your last one.

What's your plan for carb set up? OORRRRRR because it's going to be

timmy201 wrote:

something completely different...


are we going to see an injected setup :D :D :D
Author:  timmy201 [ Fri Jan 10, 2020 9:04 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
jpodge wrote:
Sounds like a cool project there Timmy and I am sure we will enjoy reading this thread just as much as we did with your last one.

What's your plan for carb set up? OORRRRRR because it's going to be

timmy201 wrote:

something completely different...


are we going to see an injected setup :D :D :D

Thanks Joe :D - not everything will be completely different!

Of course I'd love to do something crazy like a Twinky head or injection, but this one will have to stay to a reasonable budget. I think the head will just get some larger intake valves and a quick clean up. I have the 40mm Dellorto on the 1098, and in the garage I have a pair of Cooper S twin HS2 and a single HS6 SU. I do like the Dellorto as it's easy to tune, but I like the look of the twin HS2

I am planning on reusing the existing 4 synchro gearbox and flywheel (although maybe an uprated diaphragm) and possibly going back to a remote shift. I have a standard diff at the moment, so a twin pin diff would probably be a good addition.

There's some potentially big progress with the engine block to come in the next few months, so stay tuned...
Author:  timmy201 [ Wed Jan 22, 2020 4:35 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
I’ve got the crank over at St George crankshafts for a check and regrind. Then I’ve got to sort the rods so I can get the block decked to suit..

I’ll probably be looking for some A+ or Innocenti rods and sell on the 1100S rods I’ve got now
Author:  braad [ Thu Jan 23, 2020 6:29 am ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
Nice work Tim. I stumbled across your thread on the Mk1 forum, it’s a very interesting read. Seems anyone who has done this type of engine really enjoyed it, that’s got to be exciting!
Author:  timmy201 [ Thu Jan 23, 2020 7:59 am ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
Thanks Brad, the guys on the Mk1 forum are the inspiration to go down this path!

The main reason that I’ve started thinking about this project now is to collect parts as they come up for a good price, and also so I’ve got it completely planned out so I don’t have to buy things twice when I change my mind.

This week I received a high capacity water pump, set of collets and double valve springs - all brand new for less than buying just the springs locally (the guy I bought them off had them leftover from his engine build). The valve springs are the ones rated to 8000rpm, which I’m hoping the engine will have the capacity to test out!
Author:  TK [ Wed Jan 29, 2020 11:43 am ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
depends on the cam. I'm using a factory sprint cam in mine. see how it goes with an alloy head too

EDIT: Please tell me your not using C-AEA527 springs.
Author:  timmy201 [ Wed Jan 29, 2020 12:06 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
They are C-AEA526 springs. What’s the issue with the 527?

I’ve been recommended a couple of different cams, I will also need to decide on the rocker assembly before I pick anything
Author:  TK [ Thu Jan 30, 2020 6:11 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
Good mate. 526 is what you want. The 527s are crazy stiff, will rob you of power and take the tip of your cam lobes off, and stuff the tops of your valve stems. Speaking from experience.
Author:  68Rusty [ Fri Jan 31, 2020 6:40 am ]
Post subject:  Re: 1098 Engine Project - Take 2 (Big Bore)
TK wrote:
Good mate. 526 is what you want. The 527s are crazy stiff, will rob you of power and take the tip of your cam lobes off, and stuff the tops of your valve stems. Speaking from experience.
I can second that, broke top off valve and worn cam lobes from springs stiffer than required.

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Author:  timmy201 [ Fri Jan 31, 2020 7:10 am ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
Thanks guys, that's good to know. It's always unfortunate when you learn things the hard way
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