8 replies to this topic

[Merryck]

I've got a 1098cc engine. All that's missing is the head, camshaft and gearbox. I've got a 19g940 head to go on it.

 

I would like to put these together to make a nice engine, one that has a bit of power, but can be used everyday. So what cam should I go for, and what modifications to the head should I make? Is there anything I should do to the engine while it's in pieces?

 

I've never built an engine before, so I have zero idea of what I'm doing!

[Cooperman]

With a 12g940 head on a 998/1098 block, if a 'hotter' camshaft is fitted it will almost certainly be necessary to 'pocket' the block to clear the valves.

However, a 1098 engine will not really rev above about 6000 rpm due to the crankshaft limit on the long stroke engine.

Best recommendation is an MG Metro or Kent 266 cam (they are almost identical).

Lightly gas-flow the head to improve the 'breathing'.

Whilst it's in pieces and if modifying for increased power do a complete engine strip down. Measure everything accurately.

Check main & big end journals and have the crank re-ground if necessary and fit new main & big end bearing shells. Fit new crank thrust bearings to give crank float a maximum of 0.005".

Remove the pistons/rods and inspect/measure the bore wear and re-bore with new pistons if necessary.

Fir new cam bearings if the old ones are scored. Fit new cam followers.

Fit a new oil pump & timing chain.

Measure, calculate and machine to achieve a Compression ratio of between 9.75 and 10:1. You MUST measure and check the valve to block deck clearances very accurately when using the 940 head.

 

For a 1098 engine with a 266/MG Metro cam a 3.44:1 FDR is very good, or even a 3.2:1 for good cruising.

Don't rev it over 6000 rpm!

[NRB]

I would suggest an mg metro cam, I'm just finishing a new build to the same spec as yours. is yours a small or large valve 12g940? I have the small valve version and have done minor work to the ports and chambers (de-shrouding valve seats, smoothing ports) but it doesn't really require extensive work. Do some research into what compression ratio you want and whether your head has been skimmed or not, this might be something that needs addressing. I'm guessing you've read up about using a big bore head on a small bore block? With no knowledge of engine building I wouldn't take on a full rebuild unless you're keen to learn, in this instance the minimum you'll have to learn is how to time in your cam.

Edit: beaten to it, the lord has spoken ^^

Edited by NRB, 30 December 2013 - 12:25 PM.

[Vipernoir]

I've got an MG Metro cam in an 1150 and it is an utter belter.
Good torque and decent power - smooth too.

[Cooperman]

Yes, that really is an ideal cam for a 1098. Valves can usually be prevented from hitting the block deck without pocketing, maybe by being sunk into the chamber a little.

What FDR are you running? The torque at around 3000 rpm must be super.

I once had an 850 with an MG1100 engine bored +0.040" and with a flowed head and twin HS2's, etc. I ran a 3.76 FDR, which was a bit too low, but it was great to drive in the lanes. I never revved it over 6000 rpm, although I did cruise it at 5000 rpm for long journeys and had no problems.

[Vipernoir]

ST ratio S/C gearset and a 3.1 FD.
 

Waaaaaay to long in 1st (45mph indicated isn't sensible) and a ******* to get off the line, but utterly awesome once on the move.
Will cruise at silly speeds all day long.

[Cooperman]

I can believe what you say about a veeeeeery long 1st gear with that gearset.

With a high torque engine like yours and the good power band I would have thought a 'GT/S gearset would be absolutely ideal. Slightly closer than the standard gear ratios and wide enough to enable the advantages the 1098 has in terms of combined torque & power.

[Vipernoir]

The one on the workbench will be higher torque than the current one...

 

Different cam, head and capacity.

[Merryck]

That's given me a bit to think about, thanks guys! I might have to find someone to lend me a hand!