39 replies to this topic

[Retro_10s]

Don't forget that the main characteristic of the 998 will completely dissappear, that being the reviness.
1098's are noted for their torqueyness,... My std one would pull in 4th from 20mph healthily, they just don't like to rev as hard as the 998's, but you can help this bit with some choice lightening of engine components.

Personally I love 1098's to pieces. lovely motors and often overlooked.

[cap'n crunch]

1098's are noted for their torqueyness,... My std one would pull in 4th from 20mph healthily, they just don't like to rev as hard as the 998's, but you can help this bit with some choice lightening of engine components.

thats one of my main reasons for doing this, looking for a more torquey road car than a high revving car ( i rarely if not never get over 5500rpm)

Personally I love 1098's to pieces. lovely motors and often overlooked.

exactly, people often go for a 998 or 1275, hence i thought i would be different and convert my 998 to 1098.

By the way do you think a 998 cooper head would be a good addition rather than a standard 1098 head?

[Dan]

The 998 Cooper head was also standard fit for the MG versions of the A series 1098 engine, so yes. The 295 is better than the 206 version but it is now getting hard to find one that is in useable condition and they are all very old and tired lumps of iron. Unless you use the specific pistons for use with this head it will need the chamber volume matched to the engine to raise the compression ratio. It may be that standard 998 flat top pistons would work in a 1098 with this head unmachined as they may project from the block just enough at TDC but this would need very careful measuring and would do odd things to the squish band.

[fikus01]

was guna say the same, cooper heads often have low compression, mine has the maximum 60thou skimmed off it and it was ages spent making sure i could go that far with it! having said that, my 1098 hasnt lost its revvyness, ok when i built it i used arp big end bolts to make sure it all stayed together but the kent 256 cam worked wonders in it, pulls me to 6500rpm and is just as fast as a 1275 in standard form!

[stuart bowes]

apologies for thread revival if this has been covered more recently (I found this one with google)

so.. just as a sort of thought experiment:

let's say I have a 998 A+ which seems to be in good condition other than a reported loss of compression which 'might have just been the head gasket'

and I've already sourced a 202 head which I'm going to have skimmed to the right CR, and I'm getting the valve seats sorted and new guides, some porting, etc

I haven't really spent a lot of time looking a cams but lets say it ends up with an EVO1 and standard rockers

 

probably not directly relevant but I'm hoping to get it running on twin HS2's which I've already found cheap and need rebuilding

 

other variables are to be factored in no doubt but anyway

 

the question part
=============

if it turns out that it needs a rebore anyway, and lets say that +40 is sufficient, and I like the idea of more torque and im not overly interested in revs (for every day road use) and I've seen a 1098 crank on ebay for sensible money

do I then buy 1098 +40 pistons, rods to suit (or are my existing rods ok?) have the crank reground and buy crank bearings to suit (or, buy the bearings and rods and give everything to the grinder-man with with the crank and say make these fit please)

I'm a complete noob with engine building so just wanting to sound it out long before actually doing anything and see if it all makes sense / if there's anything glaringly obvious I've missed out

 

obviously I will be taking my time with it and doing a lot of reading, following step by step instructions, etc
 

this is all based on the possible outcome that a rebore ends up being necessary anyway, and just doing something a little more interesting than just rebuilding it as-is

Edited by stuart bowes, 13 September 2023 - 02:53 PM.

[stuart bowes]

and the other thing is, are all the external parts then interchangeable (pulleys, timing chain components, clutch end bits, etc)

Edited by stuart bowes, 13 September 2023 - 02:35 PM.

[DeadSquare]

1098 rods are 998 rods and "the outside bits" are the same.

 

Don't shave the head, today's fuel doesn't like it.

Don't "hang there, waiting to overtake" in 3rd at about 5,000rpm, the crank doesn't like it.

 

A 731 cam is too hot to "get off the line" in snow.

 

Always have all the parts / work done by the same company, then there is no one else to blame.

[stuart bowes]

I'm not sure I understood some of that lol

 

thanks for confirming re: interchangeable parts

 

surely I have to skim the head to get down to the right compression?  (talking about the 'new' 202 head, not the original one whatever that is)

 

the crank thing are you saying that's a downside of the 1098 crank, or the original 998 crank

 

is an A 731 the same as an evo and what's snow got to do with it ..

 

and yes it probably would all go to the same shop I suppose if nothing else it's more convenient

Edited by stuart bowes, 13 September 2023 - 03:05 PM.

[DeadSquare]

I'm not sure I understood some of that lol

 

thanks for confirming re: interchangeable parts

 

surely I have to skim the head to get down to the right compression?  (talking about the 'new' 202 head, not the original one whatever that is)

 

the crank thing are you saying that's a downside of the 1098 crank, or the original 998 crank

 

is an A 731 the same as an evo and what's snow got to do with it ..

 

and yes it probably would all go to the same shop I suppose if nothing else it's more convenient

I think you may mean, "up to the correct compression",  but if you have bigger 'pots', there is more gas to compress, so the compression ratio gets higher.  Shaving the head makes it higher still, and although that was fine in the days of 100 or even 105 octane fuel, not so good with E10 fuel.  Also, some boy-racers go mad and cut so much off the head that the valves hit the block.

 

Unless well balanced and dampened, the longer stroke of the 1098, compared to the 998, whips ( vibrates) more, and sometimes would brake, or brake the centre main cap.

 

An Evo would probably be a pleasant cam.  The 731 let the engine breath well at up to 7,000rpm, but lost all the lovely low torque.

 

Snow was slippery white stuff that often used to get dumped on the roads in winter.  The 731 didn't 'pull' much under 2,500rpm, and if you let the clutch out, even gently, at those revs, the wheels just spin.

[stuart bowes]

Ah ok the snow thing makes sense now thanks

 

I was thinking more like as you cut 'down' into the material you get closer to the right ratio, but up is more accurate fair enough

 

interesting thought about the balancing though that might be a good reason to avoid the whole thing to be fair then

[Cooperman]

A 1098 crank should be ok up to around 6200 rpm. It will go straight into a 998 block with 998 rods.
The gudgeon pin to block deck dimension is smaller so 1098 pistons are required.
Do the CR calculations after the trial build to get the combustion chamber volume correct.

[stuart bowes]

well I took a punt. saw a crank on ebay someone put starting bid £30 and it looks real clean on the bearing surfaces, so what the hell

 

I'll have it sitting there ready if we do need a bore, can give the block / crank / flywheel / rods + bearings to the same machine shop all at the same time, get them all matched up and balanced

 

and if we stick with 998 maybe someone else will take it off me for £30 or I'll just make something artistic out of it lol

Edited by stuart bowes, 16 September 2023 - 02:30 PM.

[DeadSquare]

well I took a punt. saw a crank on ebay someone put starting bid £30 and it looks real clean on the bearing surfaces, so what the hell

 

I'll have it sitting there ready if we do need a bore, can give the block / crank / flywheel / rods + bearings to the same machine shop all at the same time, get them all matched up and balanced

 

and if we stick with 998 maybe someone else will take it off me for £30 or I'll just make something artistic out of it lol

Now paint the crank all over with lots of engine oil, wrap it first in news paper, then in cling film ------  and so that your children know what it is, tie a label on it.

[stuart bowes]

well I do still have the bucket of old oil I drained out of the engine ready to be accidentally kicked over at some point. I knew it would come in handy for some other purpose

 

I keep meaning to decant it into bottles and take it to the tip, next time I do a change on the volvo I'll have at least one empty bottle to hand

Edited by stuart bowes, 16 September 2023 - 03:59 PM.

[Cooperman]

I have a friend who needs a 1098 crank for an 1160 cc project. If you don't need it let me know.