27 replies to this topic

[tommc92]

Ok here's the plan:

• 998cc A series Pocketed Block (Painted red )
• 276 or 286 camshaft
• Flat top pistons
• Ultralight Flywheel
• 12g940 head (unleaded seats, 33.3mm inlet & 29.4mm exhaust with 30° back chamfer to aid air flow, double valve springs, combustion chambers have been de-shrouded around the exhaust and inlet valves to aid air flow)
• HS4 carb
• Pressed steel rockers
• Megajolt ignition

Compression ratio will be around 9.6:1


What cam shall I go for? The 276 or 286? I'd like a bit of oomph, not bothered about a lumpy idle.

It will be in a 'daily driver' but not used in heavy traffic.


I'll keep this thread updated nice and often



Cheers, Tom

[RossKnight]

I only read about one person using the 286 in a 998 and I don't think it worked out too well, a 276 would probably be much better

I'll keep an eye on this thread, similar spec to what I want minus all the headwork and megajolt

[jaydee]

Up the CR to 10,5 really, 9,6 is too low, espescially if you're putting a hot camshaft in..
And the Hs4 is too little..i'd try an HIF44 or even twin Hs2 if you're needing some low down pull.

[PhilipGCaldwell]

hif44, if its a well ported 940 with a hot cam
go 276

[tommc92]

Okay I'll get hold of a 276

I'm going to stick with the HS4 for now as I already have one in perfect condition, but once the whole mini is done and has been running for a while I'll probably go for a HIF44

I also might see if funds allow for futher head skimming to increase the CR a bit more


I pocketed the block the other day




And also gave it a clean in the sink! Don't telll mum...

[miniman92]

I take it your buying new rings for the flat tops......... Have you managed to get hold of any, and if so where from? Are you going to hone the block yourself using a de-glazer or are you getting a machine shop to do it?

Nice progress by the way, looks like you've got the pockets nice and uniform!

[tommc92]

I am Getting them from minispares, only £33!, in +020 oversize then I'll file them down to get the correct ring gap. Yeah I've de-glazed the bores, and they're in brilliant condition so I'm happy!

Thanks that's much appreciated They turned out quite well I think, I'll get another pic of them, I've tidied them up a bit more since that picture

[miniman92]

Didn't know you could use oversized rings on standard size pistons and file them? The thing is mini piston rings are generally cast and it's quite a precision thing. They are engineered so that once the engine is up to temp, the rings begin to close to a point where the rings are then perfectly round...... Which yours wouldn't? You can sometimes buy 'file fit' rings which are just a tad oversized and engineered so that filing can be done, but don't think they are available for the A series engines?

Edited by miniman92, 03 December 2011 - 03:20 PM.

[twrminisport]

Dont file piston rings.
End of.
If you want the full details please ask and i can write you about a million pages on why :/ Failing that please use your brain and think about it

Jesus

[tommc92]

Got the flywheel, 4.3kg exactly. Maybe slightly to light for road use but oh well

[oliver122]

is it me or are the pockets not all the same size ? also is it all smoothed out as i recon if you have just gone in with say an end mill and cut it out , it wont flow that good

[tommc92]

The largest difference between the pockets is less than 0.1cc so that's fine. Yep they're all smooth and polished

[Huddley_Clubby]

I've gotten a few tips out of this for my own mini, lil 1.0 clubby engine could do with a spruce up! need to find the time and money though :S lol

[liirge]

Same Flywheel as mine if I'm correct, you have to be a bit careful with it, they are a slightly older version of the ultralights they produce today they have a reputation for having harmonic trouble i.e. excessive vibration. If you are going to use this I recommend that you balance the whole assembly on the crank. A harmonic dampener pulley is a MUST!

You will also need A LOT of packing washers to correctly space the straps for the clutch.

Edited by liirge, 04 December 2011 - 03:44 PM.

[liirge]

You can just see the packing washers under the straps to the left,