Corey's 1275 Sprite Race Motor

Started by MiniDave, May 24, 2022, 01:38:53 PM

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MiniDave

Just getting started on this build.

I have a 12 page "guide" I'm following from Kent Prather, lots and lots of little steps to do and document.

First thing we did after ordering in  a bunch of expensive race parts (rods were $1200 the set - spared no expense!) was to get it over to the machine shop to have it rough bored, so I can dry build the engine with the new pistons and take a bunch of measurements - such as how much to take off the deck so we can get the 14:1 compression ratio he wants (!) and whether we'll need to flycut the pistons to make clearance for the valves.

Also, #1 cylinder was scored on one side from the pin getting loose and rubbing on the cylinder walls, to get past that issue we had to offset the bore by 4 thou, but it cleaned up nicely so we'll be good there.

I now have the block mounted up in the engine stand so I can do that and a thousand other little tasks. Once we're happy with all that I'll take it back to the machine shop so they can bore and tap for the extra end studs and finish hone the cylinders among other things. We had thought we were going to do a 4 bolt center main cap, which would have required a line bore, but Kent thinks for the racing Corey does the stock mains will be fine. Plus too and also, I couldn't find anyone who had a small enough boring bar to do it! Or anyone who could even look at it in less than 6 months. Unlike Jeff, I don't have access to mills and lathes and such, and we're trying to make a race mid July (very unlikely, but we'll see!)

I have over 90% of the parts we'll need and an owner who's willing to spend whatever it needs to make it fast - we're shooting for 150 hp at the crank!

The head is all done, ports matched, combustion chambers reshaped and some trick 1.5 roller rockers fitted. It's also will be drilled for the end studs, I could probably do that myself, but Ima let the machine shop have at it and tap the block too.

Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

MiniDave

Measuring for thrust clearance.....right now I have zero, tho the crank turns freely (so there must be some) I've noticed I have to machine a few thou off the thrust washers on every build these days - doesn't matter who supplies them. It's a PITA but you need 3-4 thou clearance....
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

MiniDave

Oil gallery tapped for threaded plugs, also tapped a hole for a breather vent where the fuel pump would go on earlier versions of this engine. Later ones like this used an electric fuel pump so the boss is a perfect place to put a breather.

I also marked the block so we can drill and tap for two more cylinder head studs - I'll let the machine shop do this on their mill so they'll be both accurate and square to the deck.

The pistons and rods are marked and assembled, although I still have one or two more small mods to do to them before they go to be balanced.

The rotating assembly will go to Kent's shop so he can balance everything, once it's all back from the various machine shops it will be time to put it together and make some noise!

Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

Jimini II

Its all in the details, nice work as usual Dave.

cstudep

Those are some really nice looking rods......it's almost a shame nobody will ever get to see them. Of course the owner of the motor will be quite happy if nobody ever gets to see them.

MiniDave

Yeah, we def don't want them making an unexpected appearance outside the block!  :-\
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

MiniDave

I finished tapping the holes for the plugs in the oil galleries, before I could do that I had to drill out the gallery as about 1/2" just past the outside edge it necked down enough that the tap couldn't go in deep enough so that the plugs would sit flush - which three of the four must do to clear the plates that mount the engine in the front and the gearbox in the back.

I also found two more places that were originally plugged with a brass plug, those were drilled out so that the galleries could be cleaned thoroughly, so I'll drill and thread them for smaller plugs too.

I've also started doing a small modification to the rods, using a 1/8" round file I'm putting a notch at the bottom of the rod cap - this is to allow the oil a way out of the rod Kent says. I hate to mark up these gorgeous rods, but that's what needs to make it work - so we'll do it.

Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

MiniDave

The next modification I'll be doing to the block is to the oil pump area, Kent says to cut in a trough leading to the oil ports to allow a build up of oil before it goes into the pump, ensuring that the pump can always get the volume it needs.

This is a total new one to me.....I laid the gasket on the pump and marked with my thumb where the same trough is on the pump, then cut that area out, laid the gasket on the block and marked where to machine out the metal. I have a call in to Kent to ask how deep to go with this, I wouldn't think you'd want to go too deep, maybe 1/8"? We'll see what he says.....

The last pics show the notches I filed in the rod caps....

Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

MiniDave

Unfortunately, due to health reasons I had to send this one back to the owner. This morning I got a call from Kent Prather who has decided to go ahead and finish this build for Corey, since they are friends, and even tho Kent is officially retired from the race engine building business. It will be relegated to an over the winter build, to be ready for next season's races.....

Kent has already decided that a number of the parts Corey bought for this engine are "wrong" and he'll be guiding him from this point forward.
Complete failure at retirement

1989 Cooper Racing Green
2009 Clubman S
2014 Audi Allroad

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