Hitchcocks Forum

Hi Guys
I've bought a 1974 350 bullet, imported from India last august, in supposedly refurbished condition.
I've done a few miles now and noticed a small amount of slight venting at the cylinder head/barrel joint.
Upon further investigations i found 3 head bolts to be loose, so rather than retighten them and hope i stripped the head down as I've got the tank off anyway(another story). The faces are quite 'tool damaged' and i'm considering machining the head and using a composite gasket.
Its my first Royal Enfield so any comments would be helpful regarding feasibility of machining the head, max material removal, requirement for oversize head gaskets etc
Thanks Mark

Unless the damage is severe you should be OK using abrasive paper on a flat surface to lap the surfaces flat. Plate glass makes a good surface if available but I've had good results with MDF. Glue the paper down with aerosol glue and use a figure of eight motion to lap the head flat. The damage to the iron barrel should be minimal but the same method can be used.

Only you can see how much needs machining to restore flat surface, a composite gasket with wellseal should work ok on minor blemishes..

As pete says a light polishing may be all thats needed.

Don't forget there is a raised location lip on the cylinder top which needs to be machined or just filed back to allow head to fully compress gasket..

Measure the gap between head and barrel without gasket and make sure this is less than gasket thickness..

Its possible the indian "technician" has mixed and matched components.

Strange a whole line disappeared in posting..

You may have to double up on cylinder base gaskets to compensate or risk too much compression/ clearance problems, if serious machining has to be done..

Thanks for that guys, i will have another look today, and probably take advice from a proper engineer but they look fairly deep gouges. This is as i expected with the lip on the barrel too, so thanks for the tips.
Will let you know how things turn out

I've been an engineer all my working life but obviously not a proper one!
Only joking

Seriously, you can easily take quite deep gouges out with the lapping method. I'd forgotten about the lip on the barrel - that would make lapping that it a bit difficult.
If you (or your proper engineer) take more than a few thou off, heed Qwilly's advice about the compression ratio.

Don't worry about affecting the compression ratio too much - I frequently shorten the cylinder barrels on 350 and 500 Bullet engines by around 2mm in an attempt to boost the compression ratios and with standard type pistons, I usually don't even hit more than around 8:1, even without any head gasket and lapped in mating faces. Regards, Paul.

That's interesting BW. I would have thought (without doing the maths) that 2mm would have quite a big effect.
As a gutless 350 rider, does this give the 350 a bit more grunt without losing the nice "soft" feel of the engine?

Hi Pete, it surprised me, too, the first time I did it. The most I can get, with 2mm off the barrel height AND a Meteor Minor Sports piston fitted, is about 10:1, which I have in my old Indian 350, which I use as a general runabout. Even this can plod through the village at 30mph in top gear. It has terrible piston slap, due to the piston having a shortened skirt, being a cast off from one of the 350 race engines. I raised the gearing to 17t on the front and it JUST copes with it. Top speed is probably about 80 mph in favourable conditions, but it will do 60 - 65 mph all day. I did a similar 'job' on my Father's Redditch 350 café racer, this machine has the close ratio modification in the gearbox and Redditch 'R' cams and it can hit 90mph. Both bikes are still pleasant to ride at lower speeds, with plenty [more] of the torque you would expect from a standard machine. Here is mine going about its' business ...
https://www.youtube.com/watch?v=RBPg_Xj2X04
Regards, Paul.

Use wet and dry, wet on plate glass, it sticks itself to the glass when wet. You can often acquire a slab of it from an old cabinet, cheap off cuts or recovery place. Please don't use a sanding pad or wonky surface as you will get a curved surface. Keep turning the item to get a random pattern without a slope.



Tool marks? Eeek! but nevermind, some remaining scratches may be inevitable. The main thing is the surfaces need to be flat, they don't have to be mirror-polished. What we don't want is a warped surface.