23 replies to this topic

[Fruitmand]

Hi all,

After having to put the rebuild of my Mini on hold for many years, I’m slowly starting it up again. Still a lot to do and progress will be slow.

I’m also making plans for the engine. The thing is, I really want to 8 port it. I know it’s expensive and I’m not doing it to have as much power as possible. I just like to learn, try to make it work, and create my dream Mini.

The problem is, I already have a very nice A+ 1275 (now a fresh 1293) with excellent crank, which I don’t really want to replace. However, the standard con rods will not provide enough clearance for the 8 port cam.

Are there con rods available that provide enough clearance, or is it necessary to replace the crank? I contacted MiniSpares, but their I-beam steel con rods (Arrow) will not provide the clearance. SH engineering (Saenz) is unsure.

 

Any recommendations?

Edited by Fruitmand, 23 September 2024 - 08:49 PM.

[imack]

I was under the impression that you had to use a crank with 1.625" big end journals and matching rods for adequate clearance with the cam lobe.

[Fruitmand]

I was under the impression that you had to use a crank with 1.625" big end journals and matching rods for adequate clearance with the cam lobe.

 

I've read that some aftermarket con rods also provide enough clearance, even with the 1.75" journals. Would be cheaper than getting a different crank. 

[Spider]

I was under the impression that you had to use a crank with 1.625" big end journals and matching rods for adequate clearance with the cam lobe.

 

Yeap and even then you need to shave a bit off 2 of the rods.

[Shooter63]

Why don't you use a 7 port head, you get all the looks without the agro, mind you if you go 7 port buy yourself some port filler and have some fun.

Shooter

[sonscar]

Why can't you use the standard cam range?must be a reason but not obvious to me.Thanks in advance for the ensuing education.

I have a 1800 MGB and have often thought of a 8 port head but have not been sufficiently convinced.Steve..

[Tupers]

Why can't you use the standard cam range?must be a reason but not obvious to me.Thanks in advance for the ensuing education.
I have a 1800 MGB and have often thought of a 8 port head but have not been sufficiently convinced.Steve..

The Arden head used a different valve layout to a 5 or 7 port head so the cam lobes are in different positions.

[sonscar]

Aren't the holes in the block in the same place? Or is the in/ ex valve order different?Steve..

[imack]

Different intake and exhaust valve order on an Arden compared to a 5/7 port.

[Spider]

The original design of the A Series is cleverly compact, but it also can raise issues. The Cam Lobes when at the right (or wrong !) angle will contact the Big End of the Rods.

With a 5 or 7 port, the valves are (from cyl 4 to 1) E - I - I - E - E - I - I - E

 

On an 8 port, the valves are arranged I - E - I - E - I - E - I - E

 

So the Lobes on the Cams for the 8 pots are in a different sequence on the Shaft. The Inlet and Exhaust Lobes for Cylinders 2 and 4 are transposed with each other and so the Big Ends on cylinders 2 and 4 also need shaving so they clear the Cam Lobes. I'm pretty sure you need to run the Cooper S style Rods with these heads for this reason.

[Fruitmand]

Why don't you use a 7 port head, you get all the looks without the agro, mind you if you go 7 port buy yourself some port filler and have some fun.

Shooter

 

That was the initial plan, but you read about a lot of problems with bad castings, warping and other issues. Everyone seems positive about the quality of the 8 port.

 

The original design of the A Series is cleverly compact, but it also can raise issues. The Cam Lobes when at the right (or wrong !) angle will contact the Big End of the Rods.

With a 5 or 7 port, the valves are (from cyl 4 to 1) E - I - I - E - E - I - I - E

 

On an 8 port, the valves are arranged I - E - I - E - I - E - I - E

 

So the Lobes on the Cams for the 8 pots are in a different sequence on the Shaft. The Inlet and Exhaust Lobes for Cylinders 2 and 4 are transposed with each other and so the Big Ends on cylinders 2 and 4 also need shaving so they clear the Cam Lobes. I'm pretty sure you need to run the Cooper S style Rods with these heads for this reason.

 

That's good information, thanks! So would you say it's not really possible to use the 1.75" big ends?

Edited by Spider, 25 September 2024 - 01:14 AM.

[johnv]

I know where you're coming from. 

I'm the same, I have an excellent 1293 that I built and it runs great with good power, but I'd like another go. 

Current thinking .. start again from scratch, leave your engine intact and source/ build the new one at your leisure.

And then you've always got a spare if the project should need a bit of routine maintenance 

[Spider]

So would you say it's not really possible to use the 1.75" big ends?

 

From my limited 8 port experience, no.

 

I did read your comment on 'bad' 7 port castings, and yes, there are some bad ones out there, but not all. Hell of a lot cheaper as a project to do a 7 port, than an 8 and really, there's only very slight differences in the end result between them.

 

Here's some info from Special Tuning, though it predates the 1.75" Big Journal Cranks
 

 

[IronmanG]

Why don't you use a 7 port head, you get all the looks without the agro, mind you if you go 7 port buy yourself some port filler and have some fun.

Shooter

My job for the winter, filling the ports. Any tips?

[Shooter63]

Why don't you use a 7 port head, you get all the looks without the agro, mind you if you go 7 port buy yourself some port filler and have some fun.

Shooter

My job for the winter, filling the ports. Any tips?

You might want to try Belzona, I was put onto this by a guy who restores classic Lambo's which evidently suffer from crap/porous castings surprise surprise, it does take along time to fully harden and the area you use it on has to be meticulously clean but it will knock something like JB Weld into the long grass.

Shooter