Twinplug distributor clearance problem

Peterfrans · 08:49 AM

I am building a 2.7RS engine with high compression pistons and therefore needed a twinplug solution. I have bought a twinplug distributor and now have run into clearance problems. Basically the dizzy hits the fan-shroud before totally seating:

The engine is based on a early alu case modified by Ollies for mfi, larger cylinders etc, but also a larger bore (30mm) for a later distributor. Apart from the fact that the vendor is little help as his only suggestion was to grind down the mount for the fanshroud on the case the strange thing is that the dizzy does fit on a 7R case without these clearance issues. So I am also wondering if the case modification was done right. I am planning to cut my losses and buy a jb-racing dizzy as this one seems to have a more favourable design but also a bit worried about the case modification. Is the angle of the distributor hole different as later cases?

silverc4s · silverc4s's Garage

Some early ALU cases came with a larger diameter fan/fan shroud. I think that the later MG assembly will fit in its place - if you consider that a solution...

BURN-BROS · 06-14-2010, 02:45 PM

Hi Peter, you are going to have to grind the end of the distributor down...if you have enough clearance.

Peterfrans · 08:50 AM

Bill, Aaron,

Thanks for the replies. I am already using a carrera fan/alternator/fan shroud, so this should not be the problem. I don't think grinding down the distributor will work, the problem is that the part where the screw for the cap is, sits against the fan. If I turn it 45 degrees it would fit (still tight), but then the mounting to the case does not fit. Perhaps I could cut that off and have it welded on again. I will post some more pics tonight to illustrate.

ix0ifan · 06-15-2010, 01:18 AM

Peter,

Tricky problem and needs some measurements.

The early 2 litre Aluminium Case has a dizzy mounting that is:

The later casing (This is a Carrera 3) using a 30mm dizzy is:

I guess the adaptor you hav is to make the difference between the two castings.

The dizzy for the 30mm dia shaft is 40mm longer than the earlier dizzy with the 27mm dia shaft (distance over shaft ends)

Looking at the distributor in you first photograph the 'O' Ring doesn't seem to be in the correct place and I wonder if the distributor body has been modified.

The angle of the dizzy in the case doesn't change

I would also question the length of the dizzy cap adaptor, which I think is a bit short.

I needs to be similar to this

Which should then clear the fan.

Sorry about the crummy photos I just ' jury rigged' some bits to look at the basic issue.

If you have a good side on view of the dizzy (out of the engine) with a scale I can make some better measurements.

I am not sure the JB unit has an advance curve built in but this may be out of date information.

I hope this helps a little.

Peterfrans · 06-15-2010, 01:37 AM

Thanks ix0ifan,

This helps a lot. I will make some pics with a scale to explain.

JFairman · 06-15-2010, 08:56 AM

If you cut a round hole in the fan housing strap where contact is happening like some stainless steel aftermarket ones already have to make them lighter and look cool, the edge of the distributor might just fit in the hole and there may be enough clearance.

Also looks like you could easily grind a little aluminum off that lower corner of the distributor housing, ultra fine sand and polish the aluminum after the grind and make it look origonal.

and.. If the distributor is turned a little clockwise or counterclockwise and the drive gear is reindexed one tooth or more with the intermediate shaft gear the widest point of the housing will be away from the fan housing strap.
It may fit that way, and if the timing is correct like that there may be no clearance problem as it is.

tctnd · 06-15-2010, 09:16 AM

You could rotate the distributor to a spot where everything clears than make an adapter to move the crankcase stud where it's needed. Not elegant, but it wouldn't require any grinding.
regards,
Phil

ix0ifan · 06-15-2010, 10:24 AM

I have a Marelli S121 which fits the Aluminium case correctly without the need to 'cut and shut' either the fan housing or the distributor.

Surely it is just a case of making the shaft adaptor and cap adaptor to the correct length and then all will be well. Just a few more millimetres will give all the clearance needed.

kenikh · 06-15-2010, 10:59 AM

Why not clearance the fan housing and notch the strap?

Peterfrans · 08:04 AM

Quote:

Originally Posted by kenikh

Why not clearance the fan housing and notch the strap?

That was the advice the seller gave me but does not "feel" right. I would not mind to grind it down a little, but the dizzy needs to sink another 8mm into the case to be fully seated.

It would not be a problem if the orientation of the adapter plate was a bit different, as the dizzy does fit if I turn it a 60 degrees, but then the clamp is in the wrong position.

There is no problem on a 7R case although it is tighter than products from other vendors seem to be.

Finally a pic showing dimensions compared to a standard distributor.

ix0ifan · 06-16-2010, 12:27 AM

The critical dimension is from the bottom face of the mounting lug which bolts to your adaptor and the Distributor Cap mounting face.

This is about 100mm long and is idential to the Marelli that has a 30mm dia shaft.

This would, on the face of it appear to make sense BUT I am reasonably sure that the S121 was used with the 906/RSR Fan Housing which was a small diameter, 225mm vs 245mm.

I think to clear with the larger fan housing this dimension needs to increase to 135mm.

Not great news but I think this is the issue.

Peterfrans · 08:05 AM

I tend to agree with you on this. I'll double check tonight if minor modifications to the fan housing/strap/distributor will make it fit. Otherwise I'll put in on ebay and will start looking at alternatives.

All thanks for the input

ix0ifan · 06-16-2010, 03:42 AM

I will be interested to know how you get on with this.

jpnovak · 06-16-2010, 06:10 AM

This looks like poor setup on the part of the vendor. I see the #1 tick mark on the body. This commonly faces to the fan housing, even on a stock distributor. If this orientation was maintained the two 120 deg mounting points would effectively be clocked to each side of the fan support and housing.

You show this is not a problem for the 7R case but is obviously an issue when the dizzy angle is decreased relative to vertical on the early case.

I think I would find another solution. Sorry to see that since it looks like a very nicely made piece.

Peterfrans · 06-16-2010, 09:02 AM

Quote:

Originally Posted by jpnovak

This looks like poor setup on the part of the vendor. I see the #1 tick mark on the body. This commonly faces to the fan housing, even on a stock distributor. If this orientation was maintained the two 120 deg mounting points would effectively be clocked to each side of the fan support and housing.

You show this is not a problem for the 7R case but is obviously an issue when the dizzy angle is decreased relative to vertical on the early case.

I think I would find another solution. Sorry to see that since it looks like a very nicely made piece.

Indeed, especially as most examples on his site show this more favourable design and if he would have exchanged it all would have been well.

The JB racing distributor seems to have much more clearance:

Oldporsche · 06-22-2010, 10:11 PM

This distributor raceservice4u, seems to me, to be indexed incorrectly. I would contact them with the pictures you have displayed here and ask them to make it right with you.

Peterfrans · 06-23-2010, 12:21 AM

I did contact the vendor, explained the problem and sent him relevant pictures. He was not really interested. Only suggestion was to grind down the fan housing or alternatively exchange the distributor for another model, but then I needed to pay another 1000$ which does not really qualify as customer service in my book. Needless to say, I will not advice anyone to do business with this company.