Iron Head Plunger Engine Specs

[MidlandsA10]

Dear All

I've just picked up an DA10 engine, which I intend to graft the 'top end' and crank to a Plunger set of crankcases.

The barrels are relatively new with 8.5:1 +60 pistons.  I'm planning on using the original iron head.  The valves seats have been recut with new valves (standard size of 1.40" inlet valves).  What would be the recommended cam to use for a fast road bike with an iron head and mildly high compression pistons?

Kind regards

Tom

[Swarfcut]

 Tom.   356 Cam gives a good all round performance with flat top pistons. Hooligans choose the 357 cam with higher compressions, but this is maybe to be a bit too wild for a leisure ride and perhaps not such a good choice for the plunger frame's handling. I'd be more concerned about the stresses on old alloy conrods and prefer the smoother running 334 cam with dished top LC pistons. Higher compressions and that Spitfire/Rocket Cam certainly gives the performance but at the expense of smoothness and going down the full balance route will add to the costs. All depends on what you want.

 As ever, dismantle and clean out that big journal sludge trap, the centre tube comes out revealing even more filth. Bad cases may require the destruction of the tube, it can be a tenacious little devil.

 If your lucky enough to have found a thick flange barrel the crankcase studs will need to be changed for longer ones......

 Swarfy

[MidlandsA10]

Thanks for that Swarfy - very informative.

I have a 356 I bought in a job-lot so I'll put that aside for this engine.  It's my first 'big' British bike (after having a Bantam D7 and some japanese bikes) and I'm a mere 25 years old so not too worried about something a little sporty - however more interested in reliability and the ability to cover long distances so a 356 is probably the best compromise.

As another stroke of luck, the crankshaft, cylinders, pistons and top end have all come out of a post DA10 7801 engine so it is thick flanged.  Useful to know about the studs though.

Unfortunately, there's a broken fin, and being pedantic I'm planning on getting this welded up and the barrels/head powdercoated before I put the new engine together.  I'll also put in new bearings and bushes where appropriate, but hoping I can get away without having to get it balanced.

Tom

[MidlandsA10]

Hi All

I had a quote today for a cylinder fin repair (second fin from bottom) and I've been quoted £250 + VAT.. seems a little steep.

Does anyone have a steer as to if this is accurate or not?  I'm based in the East Midlands but also work in London/Cornwall on a weekly basis.

Kind regards

Tom

[Minto]

My very good friend Pete repaired a fin for me last year for free, easier to get to than yours being the bottom barrel fin, and i still had the piece that broke off and I prepped it all ready (1/2hr max). The welding took less than a minute. Then just a bit of grinding back. £250+vat????? Errrrr nope!
Jase