Matching crank case to cylinder

[Scooterlam]

Afternoon chaps' I'm looking at matching my small block casing to my GT 186 kit I've marked out on cylinder gaskit face and at the minute the walls are around 7..5 to 8mm I've used the ally packer supplied wich is a decent match to the ports on the GT barrel but I'm reluctant to fully match them as it would take the casings down to 5 mill or just under, so do I not bother at all , or would it be worth maybe taking around 1.5 to 2mm out ? I'm fitting the new GT 60/110 stroke crank and there fore will be using a packer & was worried about taking the width of the gasket face down to much .
Any advise much appreciated .

Has anyone ever quantified the gains of matching case to barrel.
I dont and Im more than happy with the results.

yes and if you did you would be even happier than you currently are

I know but that would be the first step on the path towards perfection. A long journey to an unreachable destination.
I would also have to change my unmodded small block mag housing.

[Vmakgp]

Go on go for it scooterlam ' feel the need , the need for speed ' after I'd finished I put the callipers on it & I had a healthy five MM of casing round the ports ! I just took it easy with the die grinder then files then finished of with glass paper .

[Scooterlam]

I've got unmatched casings, Wrong mag.
Split in my exhaust the inside of of the downpipe is like a bear trap.
I run static timing and a round slide 30mm carb and had a buckled back wheel..
Still puts out 22-23 bhp and 18-19 lb ft of tourque.
If I unleashed all that potential it would be unridable.

Got a new gt case on the way, I might have to change my ways.

[Vmakgp]

Lol I was tempted to order the Gt casing myself scooter lam ' looks a lovely bit of kit & made in Britain at a fraction of the cost of others
You sticking the 186 kit on it ?

[Scooterlam]

As yet undecided, but whatever it is its a big block kit,
I'm sure the GT case is set up for that stud pattern.
I have another Avanti kit with higher port timings so might go for a revvy version of what I have.
Or o might just "pour" my current set up into the new case and have a working back brake.

[Eden]

you case transfer ill be matched then but your mag cut out will be miles off ;p

[Scooterlam]

Thinking ahead already.
Doesn't Richard recomend blending a small block mag rather than a 200 one.

[Adam_Winstone]

I have another Avanti kit with higher port timings so might go for a revvy version of what I have.
Or o might just "pour" my current set up into the new case and have a working back brake.

All sounds similar to what I've been doing with mine. I'm currently putting together an Avanti motor with slightly extended port timings to see how it compares to the standard one and pre Germany I fitted Jockey Boxenstop rear brakes to 2 of my SIL cases in an attempt to get a rear brake. The brakes were instantly better but I now need to strip my Euro machine's brake for inspection as it started to squeak badly part way into the trip.

Adam

[Eden]

pity somebody hasn't some pictures to post as this is a very interesting and topical subject . I believe and hope that Scootering will be covering this in future editions.

I can see the benefit of matching the transfer ports of the casing to the 186 engine but not if it leaves insufficient mating surface on the crankcase for reliable sealing.

Why do the 186 engine castings have such over-sized transfer ports when its surely known that the small block crankcase doesn't match and would require so much material ground away to achieve a match ?

It might be interesting to build up the transfer ports on a 186 so that less material needs grinding out of the crankcase to achieve a match and best flow characteristics. Then do a comparison to see how much HP is actually lost through the slight decrease in transfer port size.

The reason that I ask this is because it seems to me that we are all just assuming that these 186 cylinders have been produced to correct tolerances and with adequate quality control . I would question that they have .......if it is necessary in every instance to grind out your stock small block casing to match the transfer ports to such an extent that there is less than adequate material left on the casing face to be able to form an adequate seal.

Too often these days manufacturers cast parts for years without any quality control checks and small errors become larger over time .

To take a case in point ...have a look at the the 20 + 'damaged' Sil crankcases and cylinders currently for sale on the Scooter Restoration site . Most if not all of the faults are due to inaccurate machining and inadequate quality control and those are just the tip of the iceburg.

With most of our parts currently being manufactured in India, I don't believe we should take anything for granted. I for one would question that the GT186 cylinders are being manufactured to the correct specification and tolerances if it is necessary to remove so much material from the stock crankcase that it is then not possible to achieve a satisfactory and reliable compression seal

Are you for real? There isn't a kit on the market that has transfer bases the same size as standard case transfers. The GT kits are made in the UK and are made to the desired specifications, if they had transfer bases the same size as the standard case transfers there would be little point in producing the kits at all.
Do you know of anyone that has a problem with the gasket face sealing or are you just presuming there is a problem in this area?
I have been taking this area of the casings out for years and out much more than the standard GT gaskets as I also increase the base transfer areas of the barrels out too and have never had a motor leak on the base gasket.
There are many photos of this work around the internet.

[Scooterlam]

pity somebody hasn't some pictures to post as this is a very interesting and topical subject . I believe and hope that Scootering will be covering this in future editions.

I can see the benefit of matching the transfer ports of the casing to the 186 engine but not if it leaves insufficient mating surface on the crankcase for reliable sealing.

Why do the 186 engine castings have such over-sized transfer ports when its surely known that the small block crankcase doesn't match and would require so much material ground away to achieve a match ?

It might be interesting to build up the transfer ports on a 186 so that less material needs grinding out of the crankcase to achieve a match and best flow characteristics. Then do a comparison to see how much HP is actually lost through the slight decrease in transfer port size.

The reason that I ask this is because it seems to me that we are all just assuming that these 186 cylinders have been produced to correct tolerances and with adequate quality control . I would question that they have .......if it is necessary in every instance to grind out your stock small block casing to match the transfer ports to such an extent that there is less than adequate material left on the casing face to be able to form an adequate seal.

Too often these days manufacturers cast parts for years without any quality control checks and small errors become larger over time .

To take a case in point ...have a look at the the 20 + 'damaged' Sil crankcases and cylinders currently for sale on the Scooter Restoration site . Most if not all of the faults are due to inaccurate machining and inadequate quality control and those are just the tip of the iceburg.

With most of our parts currently being manufactured in India, I don't believe we should take anything for granted. I for one would question that the GT186 cylinders are being manufactured to the correct specification and tolerances if it is necessary to remove so much material from the stock crankcase that it is then not possible to achieve a satisfactory and reliable compression seal

Are you for real? There isn't a kit on the market that has transfer bases the same size as standard case transfers. The GT kits are made in the UK and are made to the desired specifications, if they had transfer bases the same size as the standard case transfers there would be little point in producing the kits at all.
Do you know of anyone that has a problem with the gasket face sealing or are you just presuming there is a problem in this area?
I have been taking this area of the casings out for years and out much more than the standard GT gaskets as I also increase the base transfer areas of the barrels out too and have never had a motor leak on the base gasket.
There are many photos of this work around the internet.

And videos, lots and lots of videos.