Hitchcocks Forum

There was a case recently of compression loss on a 350 Electra (Wheaters who posted on this thread earlier), turned out to be a chunk of hard carbon flaking off from somewhere in the combustion chamber getting stuck on the (exhaust?) valve face and stopping it from seating properly.

A.

Indeed, the piece of debris was tiny but it made all the difference.

Yes, do remember, I have had the head upside down and combustion chamber filed with petrol for about 24 hours and not really gone down so guess it is not leaking all the time!

If it needs a rebore can I get oversize pistons for the AVL 500, or if not is there an alternative piston I could use?

Oversize pistons for the 500 EFI Bullet will do, these have a dished piston crown so will have a (slightly) lower compression. Failing that, an 87mm piston from the 535 CGT, but you don't want to use up all your rebores at once, surely?

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https://accessories.hitchcocksmotorcycl ... ges%2F4786

Thank you, agree EFI piston probably best way to go as mine seems to have given up, maybe when the rings broke in and as it was at top tolerance anyway it just starting leaking?

Got the valves out and look ok, are the seats supposed to stick out this far?

It looks to me as if those valve seats need some cutting and the valves lapped in.

I have seen several Electra-X cylinder heads and the ALL have the outer edges of the valve seats sticking up proud of the combustion chamber surface. I very much suspect that this wasn't part of the lean burn design.

In contrast, all the pictures of EFI heads I have seen show the valve seats rather pocketed in the combustion chamber surface. That doesn't seem right, either.

On my old Electra I had the seats cut down so that the edges were flush with the combustion chamber surface. If you don't have suitable valve seat cutters, your local engine repair place (if you have one) will cut the seats flush with the surface, they'll need a 45° cutter (maybe a 30 ° too) and a 7mm spindle.

A.

Yes it does look weird, but if I cut them right back it will reduce the effectiveness of the valve spring, think will need a shim to compensate or maybe just lap them in, inlet looks clean but the exhaust could have been leaking looking at it , never a dull moment!

Allanfox wrote: ↑

Mon May 17, 2021 11:06 am

Yes it does look weird, but if I cut them right back it will reduce the effectiveness of the valve spring, think will need a shim to compensate or maybe just lap them in, inlet looks clean but the exhaust could have been leaking looking at it , never a dull moment!

It is just a case of cutting the seats until they clean up and and lapping the valves in until they seat properly. Which they appear to be currently. (Engineers blue is needed to check or if you know how to do it smoke fitting.)

The Electra-X valve springs will cope. Mine did. Cutting the seat back will also give you a little more clearance between particularly the inlet valve head and the piston crown, there's just enough clearance with the Electra-X cams.

I know you weren't proposing this, but if you start experimenting with sportier cams, you'd quite likely have to cut a little valve pocket in the piston crown. If the valves are in the right place to start with, less material would need to be removed from the piston crown.

A.