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1098 Engine Project - Take 2 - Big Bore/Short Stroke
https://www.ausmini.com/forums/viewtopic.php?f=5&t=99579		 Page 3 of 4
Author:  timmy201 [ Wed Apr 01, 2020 2:03 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
simon k wrote:
where did you get the crank? I'd love to build one of these motors

I swapped it with a guy in South Africa for some parts. They’re a bit tricky to find now as most of them got turned into 1275 engines

There will be little progress in the next few months for obvious reasons, the next couple of stages are:
Buy some A+ conrods, get them refurbed & buy new crank bearings
Take the block for a dry build and get it decked to suit the shorter stroke
Once that’s done I’ll get the short block completed and then work on the head
Author:  TK [ Wed Apr 01, 2020 4:35 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
Hen's teeth now.
I sold two to a fella from Warwick a while back and my stock numbers are very low.
Author:  timmy201 [ Fri Apr 17, 2020 4:31 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
I tracked down some A+ rods from a running engine. They look like they’ve had an easy life as they still have factory standard size pistons and bearings fitted. They definitely are much lighter than the 1100S ones with the big lumpy caps, and are apparently lighter than the Innocenti ones too

Attachment:
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Author:  simon k [ Sat Apr 18, 2020 3:27 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
any reason not to have the journals machined down and use S type rods?
Author:  TK [ Sat Apr 18, 2020 5:33 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
why?
Author:  simon k [ Sat Apr 18, 2020 5:53 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
TK wrote:
why?


I guess that's probably a good question... and I can assume the answer to my previous question is "because there's no need to"? unless you wanted to shorten the stroke even further? edit: -3mm stroke = 1024cc

I didn't realise there was so much difference between A+ rods and 1100S-type large journal rods
Author:  TK [ Sat Apr 18, 2020 6:51 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
I don't think that you should shorten the stroke on the crank. Leave it good and strong as is. I think that if you want a 1024cc ish, then bore a 998 and put a 1275 head on it.

I think that a big bore using the stock stroke of the SA crank is a better way to go. 1250ish would be better than the 1024cc.
Author:  TK [ Sat Apr 18, 2020 7:03 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
I'll be using polished Innocenti rods.

In standard form;
Innocenti made from EN19 and weigh 675grams,
1100S large journal made from EN16 at 750 grams,
A+ made from EN15 at 650 grams
Author:  timmy201 [ Sat Apr 18, 2020 8:25 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
I had thought about swapping to the smaller journal rods, but all the guys in the UK run the 1.75" ones, and I didn't really see any good reason to get the crank ground that much. Maybe on the 3rd or 4th rebuild I might have to consider it! I think that more surface area on the bearings will give more service life too. I also don't have any S type rods, and these were probably cheaper than an S rod in similar condition.

Vizard's book has the stock Cooper S small journal rods at 690g, so heavier than the A+ and a bit more than the Innocenti ones (of course they were also made with a higher grade of material than the regular 1275 rods).
Author:  TK [ Sun Apr 19, 2020 10:33 am ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
Agreed Timmy.
Author:  simon k [ Sun Apr 19, 2020 10:51 am ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
thanks guys, sorry for the ignorant questions/comments - I've only ever worked with small journal 1275 engines... I heard about the south african cranks a few years ago but didn't have any detail
Author:  timmy201 [ Sun Apr 19, 2020 1:18 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
Don’t stop with the questions! I’ve got a very limited knowledge or these engines too, and I’m learning as I go
Author:  Scoop [ Mon Apr 20, 2020 8:40 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
Totally agree Timmy, don't stop the questions! I'm learning heaps out of this and would absolutely love one of those cranks. I will have to keep an eye out for one.
PS great work on your other engine. Looks spot on!
Author:  GR [ Tue Apr 21, 2020 9:53 pm ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
Hi Timmy
If you are going to build a short stroke engine you will have to rev it to make it go, as the 970 1071 engines really don't make a lot of power.
If you want to build a strong short stroke engine de stroke a big journal down to 1.625 size this gives you less surface area less friction, and a lot less weight to turn around at rpm.
Bore the motor to 73.5 mm this will give you 1328 cc I have built a few of these engines for people and they perform really well good torque and power.
Don't put a 1275 head on a small bore engine as they are to big for the little engines, on my formula junior race car 1100cc I have a 202 head on that making 121 HP and 93 ft lb of torque much better spread of power than the 1275 head.
Graham Russell
Author:  TK [ Wed Apr 22, 2020 10:22 am ]
Post subject:  Re: 1098 Engine Project - Take 2 - Big Bore/Short Stroke
Thank you GR.
Yes we know that the engine will like a rev. that's why we are building them. Cam choice and head etc also will come into play here in regard to power/torque band.

I certainly wouldn't be de-stroking or using small journal rods with my engine. If we want to reduce weight at RPMs I guess a lightened flywheel will do the job.

Oh you most certainly can run a 1275 head on a small bore Mini (note: not a Formula Junior race car) with great results. Nice and usable around town too.

EDIT: "there was a one-off type of engine, of which only around 40 were made, built for John Cooper’s Formula Junior race cars. It is not well known, but worth having a look at. This was based on a 950cc A-series block, with a bore of 2.661” (67.6mm) and stroke of 3” (76.2mm) – giving a capacity of 1095cc – and produced 98 hp at 7,800 rpm with a 40mm Weber. The first version used a smaller cam and twin SU carbs, and produced 94hp.

It was dry-sumped and had special rods, but the best part was the cylinder head. This engine had a small-bore head (with two casting numbers – AEA626 and 12A185) which was almost the same as the 12G295 head"

Thank you again GR
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