39 replies to this topic

[Spider]

I've done a few builds similar, though not for some time now.

The biggest issue with building any 1098 these days is finding pistons that have a small crown or even flat tops. You can go for the standard big bowl types that there seems to be plenty of and skim the head a long way down, that will help with CR but you won't gt the best from it though as it won't have much squish area. The other issue I found last time I went looking for pistons is that none in current offerings are a high performance design, with those available being a 4 (or might have been 5) ring type and split skirts.

BMC did have a Sprite piston that had a very small dish, 3 or 4 rings and a solid skirt. If you look around, there's likely some NOS sets still around.

While I think most of the other items have been covered already in this thread, just as an FYI, the stock 1098 cam was a different grind to the 998 too, it had the same profile as the low end 1275 and MKI Cooper S.

[Lplus]

I've done a few builds similar, though not for some time now.

The biggest issue with building any 1098 these days is finding pistons that have a small crown or even flat tops. You can go for the standard big bowl types that there seems to be plenty of and skim the head a long way down, that will help with CR but you won't gt the best from it though as it won't have much squish area. The other issue I found last time I went looking for pistons is that none in current offerings are a high performance design, with those available being a 4 (or might have been 5) ring type and split skirts.

BMC did have a Sprite piston that had a very small dish, 3 or 4 rings and a solid skirt. If you look around, there's likely some NOS sets still around.

While I think most of the other items have been covered already in this thread, just as an FYI, the stock 1098 cam was a different grind to the 998 too, it had the same profile as the low end 1275 and MKI Cooper S.

Keith Calvert does flat top 1098 pistons from +40 upwards.  Two ring and oil control rings.

 

Also Minimania in the states appears to sell pistons for the 8.9:1 CR midget/MG100 engine which used the 12G295 head. https://www.minimani...Mg-Midget--Mini

 

[stuart bowes]

oh well the bid was beaten in the end anyway it went just higher than I was willing to pay ( for a total shot to nothing when I don't even know if we need to bore the block yet )

 

I'll keep an eye out and if another cheap decent one comes up I'll have another go on it

[stuart bowes]

So I found a crank for £28 plus shipping, which is the right sort of price for me considering it's still a possibility and not a real plan at this point.  it looks nice and clean at least. beyond that obviously not a lot you can tell just by looking at it 

 

I had it measured before giving over the money and it's already ground down to -20 on the mains and big ends, so I guess I'll have to make that -30

 

what's the best way to go about that (just thinking WAY ahead really) do you buy -30 bearings and give them to the workshop to make them fit, what if they ring you and say actually we had to go -40 for some reason, then the bearings were a waste of money

 

or would you send just the crank in on it's own and when they tell you what they did, then order the bearings and just assume the right size ones would be a perfect fit.  just in terms of logistics really what makes more sense

 

is -30 / -40 too far to go really or is that still well within decent reasonable useable range

 

also, just to confirm if I've got this right... 998 stroked to 1098 and -40 re-bore to the block, does that make it a 1130 ? or have I worked that out wrong (it doesn't really make a lot of difference just curious to be honest)

 

this is all totally new to me I'm working this all out as I go along obviously

Edited by stuart bowes, 25 September 2023 - 09:02 PM.

[Spider]

You can just send the crank off for grinding to the next standard size without shells, however 2 'things' here if I can suggest;-

 

1. Have it crack tested. You can do a 'ring' test yourself, but that's not conclusive. If it doesn't 'ring' almost certainly it is cracked. If it does 'ring' it may have a crack starting. To do this, stand the crank on end on a decent flat surface, then dong a web with a decent size spanner, the crank should ring like a tuning fork. All the same, if it rings, have it properly tested.

2. When having any crank re-ground, find a shop that has a grinder that will hold the crank between centres. On that, they can not only correctly re-size the journals, but also correct the indexing. There's many shops about that use a chassis type centreless grinder. These will re-size the journal, but will also accentuate any errors, which can be considerable, especially on a longer stroke crank.

 

3. - OK, not on my original list ! - I'd suggest not going 'tight' on the final re-ground size. There's a tolerance range that the journal can be, aim for higher clearances/ I usually specify 3/4's towards the looser side in these ranges.

[timmy850]

You can use the website below to check the static compression ratio and the cc of the engine. A 1098 bored 040 comes up at 1132cc

https://www.classicm...cal/compression

I’ve been using a 1098 bored out 080 for a few years and it’s a really nice road engine

[stuart bowes]

brilliant thanks for the feedback I'll definitely give it a 'ding' tonight and see what happens before wasting any time or money on it then, the cost so far was definitely 'taking a punt' money so it won't be the end of the world just a bit annoying if it was duff

 

then I'll have a good ring around the local machine shops (when it comes to it) and check what machinery they use, sounds like the key thing to ask for is this indexing then, presumably they would know what I'm saying if I ask that and if they sound confused at all I should ring someone else

[Spider]

This is a chassis style grinder, though this particular one isn't but still operates on the same principal. I suggest, these are best avoided (jump to the 7:50 mark to see the action of it);-

 

They clock the wheel off the journal and each journal individually. So, where ever the average of the Crank Pin is, is where it ends up after grinding. When you take in to account where the wear is on the Pins, the end up all over the place and with odd strokes from one cylinder to the next. I think there was a thread here recently where someone experienced this. Not only do stoke lengths vary, but also just where on a 360⁰ plot, the Pins end up at too.

This is what I view as a proper style crank grinder. On this type, the whole crank is clocked in, then fixed, so the Pins all end up exactly where they should be, regardless of how they were worn;-

[stuart bowes]

I hung it by a bolt hole from one of the garage rafters and gave it a good smack with a spanner, it dinged like a bell and rang on nice and clear for like 15 seconds until I grabbed it to take it down. Seems like a good sign to start with at least

Edited by stuart bowes, 26 September 2023 - 04:46 PM.

[Spider]

I hung it by a bolt hole from one of the garage rafters and gave it a good smack with a spanner, it dinged like a bell and rang on nice and clear for like 15 seconds until I grabbed it to take it down. Seems like a good sign to start with at least

 

Sounds like you're off to a good start there