8 replies to this topic

[Deejayry]

Sometime in the not too distant future I plan to convert my mini over to EFI using a Jenvey DCOE type throttle body & a Polestar Systems ECU, in order for the setup to work well the engine will need to be fitted with a Cam Position Sensor, so I've been thinking of ways to do this.

The MPI block has a sensor mounted in the space used by the old mechanical fuel pump and the MPI cam has a suitable lobe in place of the fuel pump drive lobe. However I am using an older A+ block & the cam I have has the fuel pump drive lobe, this all makes using an MPI based setup somewhat more complicated. That is not to say it couldn't be done, I could easily make up a mounting for the sensor to fit on the fuel pump mounting but then I need to somehow arrange a lobe structure on the cam to trigger the sensor, the only way I can think of is to turn off the existing fuel pump lobe leaving a cylindrical section on the camshaft to which I could mount a split collar with a lobe to trigger the sensor. I must admit that the thought of sticking the camshaft in a lathe to turn off the fuel pump lobe is slightly terrifying!

Another way is to mount the sensor on the timing cover and pick up off of something in the timing gear, options include make up a collar that fits around the threaded end of the cam and is sandwiched in between timing gearwheel & nut, a ring or half ring that is fastened on with the vernier timing gear lock screws, clearance with the timing cover might be an issue with these two methods, the final option for the timing cover mounted sensor would be to machine away a small amount of the threaded portion of the cam so that it has a half circle section, I'm not sure how much meat is left proud of the timing gear nut but this way would not cause any clearance issues with the timing cover.

the last (and least favourite) location is to use the distributor drive and modify an old distributor body to house the sensor, this would be easy in regards to being pretty much "Plug & Play" but the space that used to be occupied by the distributor (and oil filter head) will have a front mounted radiator & associated hoses in its place.

Anyone have any thoughts on this?

Edited by Deejayry, 02 September 2017 - 09:59 AM.

[Northernpower]

Do you have to use that ECU? Most of the other ECU's use a trigger wheel on the crank damper pulley and they are readily available as an aftermarket part.

[minidaves]

just get a fuel pump blanking plate, and mount the cam sensor into it

[Northernpower]

just get a fuel pump blanking plate, and mount the cam sensor into it

The OP's problem is not mounting the sensor, it's what can he use on the cam to trigger it?

[mini13]

cams are pretty hard, I would expect you will need to use a grinding post to turn the lobe down, it shouldnt be too much of an issue though, just support the cam both ends in the lathe and turn it slowly,

 

I know a chap that had to remove lobes from a cam for a 16v conversion and he just used an angle grinder witht he cam in a lathe, but you will want a bot more precision than that if your going to mount somthing on there,

 

a couple more points, check that you can use the configuration you want, some ecu's want a small tooth, some a notch, and some a 50/50 split, and some you can change t in software. Also check where the trigger needs to be, usualyy i think its at TDC no1.

 

another option is to get hold of an MPI cam ( or compatible) and use that as a basis. what cam are you intedning to use/what engine spec?

 

another option I have heard of is tuo use aluminium screws in an alloy vernier cam drive, except for one steel one and mount the sensor through the cam back plate, I think thats only practical with a belt drive though.

[Carlos W]

What cam is in the engine?

 

I've got an MPi cam (and block) which could be for sale.

 

You could have it reground to produce a bit more power too.

[Midas Mk1]

Surely its easier changing to something like the SC kit which doesnt use the cam sensor than change blocks? I've gone from an MPi setup to SC kit fine without the cam sensor. 

[Deejayry]

cams are pretty hard, I would expect you will need to use a grinding post to turn the lobe down, it shouldnt be too much of an issue though, just support the cam both ends in the lathe and turn it slowly,

 

I know a chap that had to remove lobes from a cam for a 16v conversion and he just used an angle grinder witht he cam in a lathe, but you will want a bot more precision than that if your going to mount somthing on there,

 

a couple more points, check that you can use the configuration you want, some ecu's want a small tooth, some a notch, and some a 50/50 split, and some you can change t in software. Also check where the trigger needs to be, usualyy i think its at TDC no1.

 

another option is to get hold of an MPI cam ( or compatible) and use that as a basis. what cam are you intedning to use/what engine spec?

 

another option I have heard of is tuo use aluminium screws in an alloy vernier cam drive, except for one steel one and mount the sensor through the cam back plate, I think thats only practical with a belt drive though.

Yeah the hardness of the Cam is one of my concerns when it comes to modifying a camshaft, Neil Slark has the kit to grind off the lobe, however it is out of action for a while whilst he has his new engineering shop built.

 

The Polestar looks for a single high signal at the top of cylinder 1 compression, so can easily work with the mpi Cam, or a single tooth, Bolt or similar. Much easier than a 36-1 or 50/50 setup.

 

I have considered swapping out the bolts on my steel vernier pulleys but I'm not sure that I would trust aluminium screws in this rather critical location. Titanium would be strong enough provided that the hall effect sensor doesn't see it.

Do you have to use that ECU? Most of the other ECU's use a trigger wheel on the crank damper pulley and they are readily available as an aftermarket part.

 

For injection to work correctly on any Siamese port engine a Cam sensor is essential, the ECU needs to distinguish between cylinder 1 being at tdc of the compression stroke & cylinder 4 being at the top of its compression stroke, from a crank sensor alone you cannot tell which cylinder is at the top of the compression stroke. Oh and yes I do have to use that ECU, I already have it waiting in my parts box ready to be installed.

What cam is in the engine?

 

I've got an MPi cam (and block) which could be for sale.

 

You could have it reground to produce a bit more power too.

It's currently a Kent 286SP with the original fuel pump lobe. I have been given an mpi Cam by Neil at Slark race engineering which I may have reground at a later date.

 

Having spoken to Neil Turner at Polestar & Neil Slark I think that I am going to use an industrial hall effect sensor mounted in the timing cover and then drill & tap a hole in to the Cam gear, inline with tdc of cylinder 1 compression stroke. This method requires the least amount of machining, the ECU only reads from the Cam sensor during cranking to determine the phasing and the crank sensor supplies the master timing, this means that the alignment of the Cam sensor does not need to be super accurate.

 

 

Edited by Deejayry, 02 September 2017 - 10:30 AM.

[Northernpower]

Do you have to use that ECU? Most of the other ECU's use a trigger wheel on the crank damper pulley and they are readily available as an aftermarket part.

 
For injection to work correctly on any Siamese port engine a Cam sensor is essential the ECU needs to distinguish between cylinder 1 being at tdc of the compression stroke & cylinder 4 being at the top of its compression stroke, from a crank sensor alone you cannot tell which cylinder is at the top of the compression stroke. Oh and yes I do have to use that ECU, I already have it waiting in my parts box ready to be installed.

Thanks for that, I didn't realise how the siamese port injection worked

Edited by Northernpower, 02 September 2017 - 10:30 AM.