28 replies to this topic

[maystro]

@whistler yeah good Aussie ingenuity, that Russell guy is at the top of the game ?

[PoolGuy]

Mine adds up to 1166cc, I haven't had any head gasket issues yet. 
 
The minispares site says the C-AEA647 gasket is good up to +100 overbores. If you are going for a 68mm bore I think you need to go a 1275 head gasket

That’s correct, and you need to have the head modified to suit with regard to the water ways.

Thanks Timmy and Whistler for the info on your 1098++++ motors.

[maystro]

@poolguy what do you mean about changing the water ways? I'm running a 998 with a 12g202 head which is a 1100 head. If that is needed I'm hoping it had been done before I bought my motor which has had a hard long life.
Oh yeah now is the time to tell me this because my head is in the machine shop and just got quoted $850 bucks for a full recond.
That's my other question so since this 12g202 head of mine has been running on my 998 block do I have to do anything else if I want to add this to a stroked short block?

Edited by maystro, 17 April 2020 - 10:36 AM.

[timmy850]

The coolant passages only need to be modified if you’re going for 68mm pistons - which is like +130” overbore. You don’t need to worry for most builds.

Head reconditioning is pretty expensive, but a lot of work goes in. You just need to make sure the compression ratio is going to be suitable as the extra stroke adds compression

[PoolGuy]

Pretty much as Timmy says. Graham Russell explains it here http://russellengine...ct-68mm-part-1/

[maystro]

Thanks guys,  so for me to make my 998 A+ block into a 1098 I can get some modified short skirt pistons which will fit my 998 crank without the need for the longer stroke of the 1098 crank?  

[timmy850]

You need the crank and pistons - otherwise they’ll be miles away from the top of the block and you’ll have very little compression

[Spider]

Thanks guys,  so for me to make my 998 A+ block into a 1098 I can get some modified short skirt pistons which will fit my 998 crank without the need for the longer stroke of the 1098 crank?  

 

You'd just use 1100 Pistons.

 

eg  https://minisport.co...s-cast-ring-set

 

I think as a standard engine, you'd be rather happy with an 1100 over a 998. If reconditioning a 998, then the only added cost really is the 1100 crankshaft on top of the standard reconditioning costs.

 

Up to you, but personally, I don't think they are worth spending the money on to get better performance from them. The dollars vs output to me doesn't stack up when compared to a 1275 that will last a lot longer in any case as it has a better bottom end.

 

The 1100 engine, as stated elsewhere is a small bore long stoke engine. Therefore, right off the bat Valve sizes are rather limited and the key to better performance from these engines is all locked up in the head and valves. The money you would spend on having a head done (before anything else) will cover the purchase price of a 1275 with change. Then you need to have the rest of the engine done, which will be similar in cost to the same for a 1275. There's also a much wider choice of parts available for the 1275.

[maystro]

Thanks Spider man,

I wish I had read this post before I just sent my 12g202 head into the machine shop to get recond.  It already has double valve springs and big valves and a ported head so just getting it cleaned up is costing me $850 bucks.  That is re skimmed and new valve guides, seals and hardened seats, reground valves but no extra porting which I probably wouldn't trust to a local mob.  But anyway this will probably keep me going for the next 12 months before I'm intending on doing a big rebuild.  

 

Can you please elaborate about the 1275's having better bottom ends than 998's.  I have an original 1981 A+ 998 except for being over bored 40 though.  I thought the A+'s had better cranks than A series no matter if they were 998 or 1275's?
 

I remember when I got the gear box done up it cost heaps extra because I had to get an A+ main shaft which was a lot bigger than the smaller A series.  

It's like you know me and I probably wouldn't be happy with the 1100 motor when I know there is a 1275 available and I'm probably going to be doing up the bottom end in 12 months which is going to take the same amount of man hours which equals dollars to re build. 

So my other question is where do you find a 1275 motor for the price of doing up a 1100 head in Australia and should I be sourcing a A+ or just A series unit?

Cheers 

Brad

[Spider]

Without needing to bog down on a lot of detail, right off the bat, the Bearing Sizes of the 1275 Engines are considerably bigger than the small bore engines. You won't damage or break either, but, because the 1275 has bigger bearings, the bearing area is substantially bigger. This lowers the spot pressures on the bearings, which in turn leads to lower spot oil temperatures, which leads to longer oil life and so should lead on to longer engine life. The Cranks are considerable stouter in the 1275 over the 998 and in particular the 1100 types, not that you'll break any of them (though, it's not out of the question!) but the 1275 crank will flex and twist in normal use way less than the smaller engines, which again, leads to lower oil spot temps.

 

A+ 1275 Con Rods are lighter than the small bore Rods. This helps not only in lowering the mass that needs to be accelerated (and decelerated) but also with critical harmonics in the bottom end, which again, lead to lower spot oil temps.

 

The bigger Bore of the 1275 is more conducive to ring sealing than a small bore, particularly at higher revs.

 

The stroke of the 1275 is less than that of the 1100 engine, so piston peak speeds are less, leading to longer ring life and lower spot oil temps.

 

The decks are generally heavier on the 1275 engines, usually leading to better gasket performance.

 

A or A+ for what you will be doing really is academic. Here in Aust, you'll usually pay a lot more for an A+ and really, for no advantage, in fact, I actually prefer the pre-A+ blocks.

 

Where to find them ?  Probably ebay is a waste of time, but, you never know. Facebook is always worth a look. Ask around some of the clubs etc. Be patient and the right engine at a realistic price will show up.

[whistler]

Had first start up yesterdday; took it up to 2/2500 rpm after to bed the cam and followers in. Going to retorque head and sort tappets out today.

https://www.facebook...429308034/?t=18

 

It sounds better today after sorting the valve clearances out; like a sewing machine. Just need the appropriate exhaust manifold and a HIF44 now and it's ready to go in my mk1, if the shell ever gets done.

Edited by whistler, 19 April 2020 - 11:21 AM.

[maystro]

Thanks Spider man,  you did answer a lot of questions I had about my transition from 998 to 1275 which is inevitable.  

So in an ideal world is an A+ 1275 block better than a 1275 A series especially when my electronic distributor is a A+, because I don't think that will fit on a A block?   Also is their going to be any probs and can I use my A+ 998 gearbox on a 1275?  

[Spider]

In regards to your electronic distributor, is it a programmable type ? What ever distributor you do use, it will need an advance curve to suit what ever engine and spec of engine you decide to run with.

 

I've found the 1275 A+ blocks had some pretty poor machining done to them right from the factory and so need extra work to sort them out. I also don't like the grade of cast iron that they are made from.

 

Your gearbox will be fine under a 1275, however, you'll either need a 1275 primary gear, or, if your 998 one has a good back bush in it, modify the other end of it to suit the 1275 crank.

[maystro]

Thanks mate, I'll be asking a few more questions down the track.

 
Cheers buddy