Compression
Turbo Mini Forums

Hi guys, this is a N/A question, but I figured this is a better forum for advice like this, as opposed to TMF... Anyway.

Recently got my mini MoT'd etc, after a full rebuild.

Engine Specs

1310
Omega +0.40" forged pistons with a 6cc dish.
SW5-07 Cam
Crank has been Hardened and balanced
Lightened & balanced flywheel
Duplex timing

Now, this block has been skimmed and decked a few times, how much, i'm unsure. It was done before i owned it.

The pistons are flat with the deck. And the head im currently using is completely standard at the minute.

The car was starting perfecting, on the key, everytime, until recently.

She burnt out 2 starters, and then with the new one, everything seemed fine.

Then the starter began to get sticky and tired again.

I checked the current going to the solenoid, 12V before and after, and remains at 12V until the key is turned, where it drops to anywhere between 6v and 2v (while the strater is trying to turn over)

I checked the compression in each chamber, and instead of 12, it's at 16!

With two 12V batterys wired up, the starter fires over the engine fine and gets her going, still 12V not 24V.

Now, this is all well and good, but this is only a temporary fix.

I could get myself a High Torque starter motor, but will the high compression absolutely rape my shell bearings?

N. Ireland Mini Forum: http://www.mini-chat.co.uk

Inertia or pre engaged? and are you depressing the clutch while turning the engine over?

it sounds like the static compression is reasonably high, at least 10.5:1 or above with a cranking pressure of 16 bar on the SW5. The inertia starter will struggle but will work, only if you do not depress the clutch.

Thanks for the fast reply.

It's inertia.

I'm not pressing on the clutch, If I do press on the clutch, the engine simply won't start.

I've successfully burnt out two starters as they just get very very tired after continued attempts.

I was thinking of getting a high torque inertia starter motor to solve the issue, but i'm concerned what effect the high compression will have on the engine.

If it'll need rebuilt in a year, I may aswell do it now, with new block.

N. Ireland Mini Forum: http://www.mini-chat.co.uk

Your high compression won't cause you problems with the bottom end. Think how much pressure we get in a boosted car, and they are fine.

I would check your main cable from the battery to the starter and the main earth. The starter can obviously do the job, but the battery is not supplying enough current. A high torque starter is an option, but check the power source first.

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I tried a single battery, directly to the starter and engine for earth, and it still had trouble.

The two batteries in the boot was the only combination that worked. Other than one in the boot and one at the engine. Which is the same anyway.

The power supply was fine going up to the engine a couple of weeks ago, until the standard starter began to get a bit tired.

I'll double check all the cables anyway, might even stick new ones on, but surely if something was wrong, they would get hot? As if there was a bad earth?

N. Ireland Mini Forum: http://www.mini-chat.co.uk

Is the shsft on the starter covered in clutch dust? Try cleaning and greasing it.
Mine was always fine with 12.5:1 cr

Paul

I seriously doubt it!

Yeh, but what were your cranking pressures Paul. I had horrendous problems with the inertia starter and high cranking pressures of 16.5 bar, but I never burnt a starter out.

I never had a problem that required me to check my cranking pressure, I wouldnt know Colin

I seriously doubt it!

Thanks guy!

Yeh paul i cleaned the starter motor shaft, and made sure it was moving back and forward freely.

I guess i'll be ordering a high torque inertia starter then!

Thanks for the help guys, i'll post with updates soon i guess!

N. Ireland Mini Forum: http://www.mini-chat.co.uk

if connecting 2 batteries in parallel is the only sure way of making it turn over and fire is that not pointing at a weak battery? maybe the cold crank rating of the battery simply isnt high enough for the high compression engine
and the 2 burnt out starters could be because you have been on the key for say 5 minutes turning it over and they just over heated?

Yes i moved to the darkside

Instagram @jdm_brett

I think the starter problem is only the begining of other problems unless Shell V power and an optimised ignition advance curve are used and properly set up on the rollers with Det cans

The batteries I used were both fully charged.

One had a 300 amp starting power, and the other was the same as used in a peugot diesel. Both new (I know thats not a guarentee)

I'll have to try and find someone in N. Ireland then capable of setting up a mini on some rollers, they're few and far between if they exist to be honest.

Forgive me, but what to you mean Sprocket by Shell V power?

N. Ireland Mini Forum: http://www.mini-chat.co.uk

99 octane fuel

Ah I see, well im running her on premium unleaded from at the minute.

I think i'll fit the aldon dizzy i have lying around aswell.

N. Ireland Mini Forum: http://www.mini-chat.co.uk

re attach New earths to the engine from the body work at least 2 and ........ make 2 good ones from the battry to the bodywork

I think you have a wiring fault. There must be a fault for the voltage to drop that much when cranking.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Well, the front wiring loom in the car is piece together from a couple of different minis.

Maybe I should just bite the bullet and buy a new front loom?

N. Ireland Mini Forum: http://www.mini-chat.co.uk

I would start by measuring the resistance of the feed wire and ensuring you have a decent connection to the battery and starter.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

Here's an idea:

If i go and get myself two lengths of battery cable.

1 to replace the current positive cable running under the car.

The next would follow the same route, but run from the negative terminal straight onto the starter, where it bolts to the engine.

That would provide the car with a pretty bomb proof earth and positive.

It's also one of the cheapest options available at the minute.

N. Ireland Mini Forum: http://www.mini-chat.co.uk

A SW5 with 10.5:1 compression might be much harder to turn over than a 296 on a 11.5:1.

BTW, the SW5 shouldn't have much more than 10-10,5:1 in comp according to Swift.

So is something terribly wrong ?

Or has the block been skimmed way to much?

N. Ireland Mini Forum: http://www.mini-chat.co.uk

An update for those who could GAF.

Ran a cable from the negative on the battery the whole way up to the one of the bolts that holds the starter to the clutch housing.

Starts great now.

So there's (was) obviously an earthing issue with the engine, that was tempermental at best.

I'm gonna re-new the old earth aswell, just because stuff like that annoys me.

Cheers for the help!

N. Ireland Mini Forum: http://www.mini-chat.co.uk

I GAF Dez

Paul

I seriously doubt it!

Cool,

easy fix in the end.

a high resistane earth can be a bugger to trace as they can low restisance when your looking for them... sods law!

Lol Paul!

Yeh, just one of those problems, and it is a mini afterall; turns out my speedo cable is now broken.

Oh the endless issues!

N. Ireland Mini Forum: http://www.mini-chat.co.uk