Houston, do we have a problem?

[Davidb]

I am finally starting to assemble the new engine for my Elan. Ex-Formula Atlantic Laystall billet crank, "Maxspeeding" rods, CP pistons and what seems to be a very good block. The jack shaft and crankshaft installed fine and clearances check Ok. Then I installed #1 piston and rod--problem! The connecting rod hits the jack shaft. I have read as much as I can on fitting the longer stroke cranks but I don't recall ever hearing of this problem. The jack shaft will have to be relieved by about 3/16 to permit the rod to pass. It is the original, short, cast iron unit.
Anybody foresee a problem?

[rgh0]

Yes it happens depending on the rods and crsnk used when building a big capacity engine. Reducing the diameter of the jackshaft is what is required. If your worried about the diameter reduction weakening the jackshaft to much get a steel one made.

cheers
Rohan

[oldchieft]

What stroke is your crank?

I fitted a 84mm crank into a 711 block with no problem, but i would not think the block makes a difference.

Jon the Chief

[Elan45]

The distance from crank center to jackshaft/ camshaft center is the same on all Kent engines. I wonder if there is a wider cross-section to the rods too, but I would side w/ Rohan and get a steel jackshaft. I'll bet you could get one from a vendor selling BDA type components.

If you've got clearance w/ #1 rod, you'll also have issues w/ #2 also and if you use a full length cam/ jackshaft, the other 2 as well.

Roger

[el-saturn]

......if your just running the distributor, i'm sure you can reduce the dia. in those areas by up to 5 mil or a 10mm dia solid is enough - don't even need to whip out my 11c or 41cv!! sandy

[CBUEB1771]

......if your just running the distributor, i'm sure you can reduce the dia. in those areas by up to 5 mil or a 10mm dia solid is enough - don't even need to whip out my 11c or 41cv!! sandy

The jack shaft still has to support the bending load imparted by the timing chain so you can't whittle everything away.

[Davidb]

After considering the advice here and getting more advice--i.e. A steel jackshaft would require bronze gears on the oil pump and distributor, new replacement parts are not made to original drawings raising the possibility of problems (I think that came from "Chancer" on this forum. I also talked to John McCoy who is just 'down the road' from me and he said the last steel jackshaft he bought was made in China and needed extensive work to be usable. John advised machining down the existing shaft as did Nick Stagg in the UK. so that is what we did-it looks good to me:

[promotor]

That looks like it'll do the trick.

I have sawn a few standard crossflow camshafts in two - to say that the material is tough is an understatement. When I got 3/4 of the way through one and had blunted two saw blades (and ruined my arms and wrists!!) I was amazed by how tough the material was and decided to test it's breaking strength with a big hammer and chisel! I could not break the cam at the cut with only a 1/4 of the material holding it together! Of course a bigger hammer and a decent chisel would have done it but by this time my saw had a new blade and I had more determination to cut through it!

Considering that your modified jackshaft isn't much thinner than a reprofiled crossflow camshaft that can run on mega stiff valve springs without breaking I'm sure what you've got there will be more than adequate for revs not beyond 7000rpm while only having the requirement of turning the oil pump / fuel pump and distributor. Admittedly the oil pump is a fair old strain on a cam skew gear but there's more than enough material to handle a wet-sump oil pump on your jackshaft.

[Davidb]

One small advantage of machining down the original jackshaft is that we could see how out-of-round it was while on the lathe! It must have been contributing some amount of vibration to the engine.