Fast road / race 1098 - your thoughts please.

Post by **Pandora** » Wed Mar 01, 2006 10:20 pm

Hello all,
I'm new to Moggy engines, (but have tinkered with the odd mini in the past) so am looking for a bit of clarification on some points in 'Vizard'....

I'm building a 1098 for my '60s sports racer (Mid engined, VW transaxle etc) It originally ran with a 997 engine in the 1100cc class.

I have a good 1098 engine, bought as a runner. I have also sourced a period 649 cam, a nicely ported 295 head which I'm planning to up the valve sizes on slightly and I've lightened the flywheel. The car will only have occasional road use, so I'm not too woried that it might not be the most tractable vehicle in Tescos carpark..... despite Vizards claims that the long stroke makes it more tolerant of the 649

My question is - where can I get decent pistons? Vizard recomends Powermax flat tops, but of course these are unobtainable. 998 A+ pistons would be ideal, but are the wrong length. What are the best of the standard dished pistons to use?

One thought I had was that if I was to get the block decked, I could machine down the piston crown as well - uping the comp ratio. How much can you machine off the block without hitting the water ways?

My worry is that to get the comp ratio i want (approx 10.5:1) I'd have to take a load off the head, and then it's no use if i manage to get better pistons later. (I have access to a spare block)

Any suggestions?

Also, I'm going to replace the standard bottom pulley with a damped one (If I can get the bugger off - the nut was fine but the pulley is stuck!!), but any thoughts on a safe rev limit for a 1098?

Cheers,

Alastair Brown
Nr Edinburgh

Post by **ian-s** » Thu Mar 02, 2006 10:51 am

Hi Alistair
You can get 1098 pistons with solid skirt and in race material from JP pistons in Oz : http://www.jp.com.au/
I had a couple of sets when I built a 1098 for my Formula junior racer. delivery is quite quick
. I'll send you some pictures if I can find them

Post by **Cam** » Thu Mar 02, 2006 12:50 pm

Get in contact with MED racing engines or Simon from Morspeed.

http://www.med-engineering.co.uk/home.php

http://morspeed.co.uk/

Both are experts in building A-series race engines and will be able to supply what you need. I got my Omega pistons from them after being told that they are no longer available.

Post by **Pandora** » Thu Mar 02, 2006 6:05 pm

"I had a couple of sets when I built a 1098 for my Formula junior racer....."

Any chance you could give me some more details of the spec you settled on?

What mods to crank/rods etc? comp ratio? rev limit etc.

Any info would be much appreciated, as it is efectively a FJ engine spec I am looking for (on a budget)

Post by **bmcecosse** » Thu Mar 02, 2006 7:50 pm

The 649 cam is really far too wild for a 1098 - it breaks if you rev it much beyond 6000 for any length of time, and so you will not the best from that cam. Far better with a 544 - I found this many years ago with a full race 998 I ran - tried the 649, lost lots low down and gained nothing at the top compared to the 544 - and i was revving it to well over 8000 ! Won a couple of Sprints at Ingliston (1 litre class) and then eventually rolled the car at an autocross in a field just opposite Ingliston, behind the BP filling station. You will also do far better to use a 1275 heda - the 12g940 or even a genuine S head (AEG 163) which is what I had on that engine. You MUST fit a crank damper and best mod by far will be to lighten the flywheel as much as seems sane - to help acceleration AND to help crankshaft life.
It would actually be a better bet to use a 948 crank and bore the block out to get extra capacity. That can be revved to around 8000 ok provided it has the damper and the light flywheel, and will ultimately give more power than the long stroke 1098.

Post by **Pandora** » Thu Mar 02, 2006 8:03 pm

Interesting.....

Is the 948 crank not weaker than the 1098? though I can see that the shorter stroke would help with rev limit.

Surely I'd need quite a large overbore to go out to around 1100 (perhaps that's where the orig 997 size came in?)

Am I right in thinking that with a 940 or 'S' head I'd need to pocket the block - not such a chore given the work going into the engine anyway, I supose

Any suggestions of pistons & rods to use with 948 crank. I see from Vizard that Imp pistons can be used, but you need to offset bore the block - and it'd take me beyond the 1100cc

Funilly enough, the guy who lightened the flywheel for me and built the parts to mate engine to transaxle used to be based just behind the BP station over the road from Ingliston! Small world....

There are a few more jobs coming his way as well!!!

Post by **bmcecosse** » Thu Mar 02, 2006 8:15 pm

Yes you would need to pocket the block - dead easy, and you can sell the 295 head for far more than a 940 costs. In fact I bought an MG 940 (bigger inlet valves) at Ingliston classic car show last summer for £20! The 948 crank is plenty strong - but must have the damper, and ideally should be balanced of course. The 948 rods are hopelessly weak (clamp bolt small end) - hence use the 1098 rods and Mini 998 pistons - at +60 these will give ~ 1060 cc - not significantly less than 1098 and far more revvy!

Post by **Pandora** » Thu Mar 02, 2006 8:57 pm

Excellent, Anyone got a 948 crank? +60 998 Pistons?

Off you all go to look under the work bench!

Seriously though, this sounds like a nice combination, but one further question - using this combination, will piston crown be OK with block deck face, or will either require machining down (other than pocketing block if I use a 940 head).

Is there a parts for sale section on this forum? I'm off to look....

Post by **Pandora** » Thu Mar 02, 2006 10:09 pm

Just sat down with Vizard and a calculator.......

Basically, as the stroke is the same, overboring a 948 to take 998 pistons will give me 998cc - the same as the original spec for the car, so that'll be easiest solution, rather than having to deck so much off the 1098 block and still have to find a 948 crank

Also, given the 'Historical accuracy' to the cars orig spec. I recon I'll stick to standard bore pistons rather than going for the +60s

It'll be lumpy with the 649 cam, but never mind

Anyone know what I should pay for a decent 948 engine? (anyone want to swap for a 1098?)

Post by **rayofleamington** » Thu Mar 02, 2006 10:20 pm

I was under the impression that BMC was meaning to go for +60 pistons on the 998 size (ie 1.5 mm bigger than the 998 piston) to give 1060cc

948 engines are not too hard to get as many people opt for the 1098.
if you're going to bore out, change big end shells, cam etc.. then would you accept a 'rough' engine? They come a lot cheaper than 'decent' engines.

Post by **Pandora** » Fri Mar 03, 2006 6:05 pm

yes, I think ther'd be little point in paying the extra for a good engine only to strip it out. So I supose, all I really need is just Crank and Block from 948, I'll use 998 A+ rods as well as pistons. Pretty much everything else will be replaced or carried over from 1098 stuff I have.

Are Clutch / flywheels the same?

You are right, the suggestion was that +60 woult take me up to 1060cc, but as car was originally raced as a 998, I recon I'd stick to that (not least 'cause pistons are easier to get!)

Still not totally ruling out building the 1098 if I can get the pistons though, as Vizard recons it's more suited to the cam

I have always said I'd have a car with a 649, and if ever there was a car to have one, this is it!

Post by **rayofleamington** » Fri Mar 03, 2006 6:47 pm

yes, I think ther'd be little point in paying the extra for a good engine only to strip it out. So I supose, all I really need is just Crank and Block from 948

I've got a 948 engine that was 'rebuilt' by the previous owner but I didn't use it as I didn't have time to investigate it. He'd left the plugs out for many years - I'd expect some rust in the bores.

It's not really worth shipping - do you ever get down to the midlands?

Post by **bmcecosse** » Fri Mar 03, 2006 7:17 pm

If you use a 948 block with a fancy cam - you will need to fit cam bearings into the block which is a very expensive process. So use the 1098 block - it's otherwise the same, but has cam bearings already installed! I thought you wanted 1100 cc - hence the +60 suggestion - if you only want 998 then you actually just fit 948 crank and Mini 998 pistons and rods in the 1098 block - no need to deck it. If you insist on using a 948 block you actually need to bore it +65 thou to use standard Mini 998 pistons.
I can assure you the 649 cam will be a mistake - I ran my autocross/sprint Mini on a 544 and it was great, changed to the 649 and regretted it - changed back to the 544, much better again. The 649 loses lots low down and gains very very little at the top - especially on a small bore engine running a nice big-valve head where there is plenty of breathing capability. The extra lift of the 649 (and slightly longer timing) is more beneficial on the bigger capacity engines which are trying to breath through the same head - the breathing is more difficult and so every little extra lift/timing helps - but it's just a menace on the smaller engine.

Post by **Pandora** » Fri Mar 03, 2006 9:00 pm

Many thanks to ray of Lymington, But I'm afraid I'm not down south much, so will have to keep an eye out for a crank which can be posted rather than a full engine.

Spoken with JP Pistons in Australia - recon that's the way I'll go for now, with the option to rebuild in future with a 948 crank and Mini Pistons.

Here's to many nights in the garage! (until the baby arrives in a month, then who knows when I'll get round to it.....maybe for when it can drive!)

Post by **ian-s** » Sat Mar 04, 2006 9:58 am

If youre going to enter in an 1100 cc class you're going to have to keep to a standard size bore as even a .010 bore will take you above 1100.
The part number you want from JP is JP0553A , but get them in race material and solid skirt.If you send me a pm with your email address, I'll send some photos of the pistons.

Ian

Post by **Pandora** » Wed May 03, 2006 4:35 pm

Hi all,

Just had a thought......

I have recently found a set of original 998 D crown Cooper pistons and a set of Mini Miglia Slipper pistons (Which themselves are quite rare). As the compression height on both of these is too high for 1098, can i get away with machining down the crown? (approx 3mm to be taken off to face them with the deck of the block)

crown thickness on either type seems to be about 6-7mm, so would involve approx halfing this, and then on the cooper pistons I'd leave off the top ring as it'd be too close to the top face. I'm just a bit worried this will leave the crown too thin....

Has anyone ever tried this as a mod on a 1098? I just can't bring myself to spend the cash (about £180 by the time post, tax etc added) on a set of pistons from Australia without seeing them first if there is an alternative. It's not that I'm tight, honest!

I'd probably modify the Slipper pistons and keep the Cooper 'D' ones for a future 948/998 as discussed above, but before I go ahead I'd appreciate any words of caution bourne from experience.

Thanks

Post by **rayofleamington** » Wed May 03, 2006 5:53 pm

On a tuned engine, I expect it is a pretty bad idea to half the crown thickness. Not to mention the problems you'll get by loosing the top ring

I'm no tuning expert but bith of those suggestions seem very bad engineering practise!

Post by **ian-s** » Wed May 03, 2006 6:21 pm

It would leave the pistons very weak if you machine that much off the crown . If they could run with only a 3mm crown thickness they would have designed them that way. Far better put them on Ebay or sell them through the Mini7 club and buy the right pistons.

Post by **bmcecosse** » Wed May 03, 2006 9:01 pm

It sounds a bit too much to me. These pistons will fetch really good prices on ebay - or try Minifinity forum.
It's actually at bit more than 3 mm - 142 thou ~ 3.5mm. Too much.
Far better to get a 948 crank and use these pistons with con-rods from a 998 Mini. It will rev higher and give the same ultimate power as the 1098 for the same state of tuning.

Post by **RobThomas** » Thu May 11, 2006 6:45 pm

What about the later MG 1098 block with the larger crank journals and rods? Stronger than 1098 Minor engines.