These two photos show the extent of the valve seat recession on the exhaust valves, and the concentric ridges on the sealing faces, where I would expect a dull grey smooth surface. You can feel the ridges under your finger nail. Chris has identified my dilemma - I would really like to get the block skimmed and renew the valve seats, but this is my first Seven and I want to get it out on the road. My plan is to buy a new set of valves and and a valve seat cutter, which should enable me to then lap the valves in with the minimum removal of material from the block.
An alternative in the short term would be to put everything back together as is and see what happens. Compressions were all about 80psi (cold, dry, starting handle, manifolds off), except when the valves were sticking. Adding oil made no difference, so I am confident the piston rings are OK.
Interested in the thoughts of them as knows though.
Hmm. The valve you're holding has a good margin (the amount of material above the 45° seat on the valve head). Is that exhaust valve that's still in the block in the same condition; or does it have something approaching a razor edge there?
(30-03-2018, 06:01 PM)Stuart Giles Wrote: Hmm. The valve you're holding has a good margin (the amount of material above the 45° seat on the valve head). Is that exhaust valve that's still in the block in the same condition; or does it have something approaching a razor edge there?
The valve from the block is the one at top and has a slightly wider seat than the valve from the previous photo, but still has a bit to go to reach the edge.
It is very hard to be sure from your pictures but something looks very odd about the exposed valve seat, almost as though someone has fitted inserts below the face of the block??? There would appear to be a definite step down to the valve seat, if it was not for that I would have suggested your plan for a new set of valves and a clean up of the seats would be all that is required, perhaps someone has put a 30 degree cut above the seat to reduce shrouding, in which case run with plan A!
Ian is on the money there, looks to me as though the seat has been narrowed from above.
The width of the seat in the block looks good, as does the valve .Although the recession is not ideal, it will not affect performance significantly. I have seen a number of engines like this.
I would regrind the valves, and reassemble.Looking at the valves I would’t renew them, you could get them refaced at your local engine reconditioners £2 - 3 each if you are really bothered.
Beware of cheap diy valve seat cutters, they will spoil what you have.You would need something like a Neway seat cutter, they are excellent, but expensive £250ish for 1 cutter, pilot, and handle.Bear in mind a recut will lower the valves even more.
Hope this helps and you get your Seven going shortly
I have decided to lap new valves into the existing seats and see where I get to. A previous owner had the engine rebored by a professional outfit 10 years (but only 1000 miles) ago and had new valve guides at the same time, and I assume new valves as well. Quite why they didn't skim the block and do valve inserts while it was in bits is a bit puzzling. The car is a 1934 Type 65 and the sports engine has the original, or at least original spec, crankshaft, so at some point I expect to rebuild it to get the crank crack tested and check the rear bearing. I'll skim the Chromidium block and get hardened valve seat inserts done at that time.
The angle across the block and valve seat and into the port appears to be a straight 45°. I think it's just the crud above the seat that gives the stepped appearance Ian referred to. Attached photo is number one exhaust which I have started to reface using the old valve, and which I think should then lap in ok with a new valve.
Just wanting to get it on the road in time for the sunshine, although it was snowing here in Leeds this morning, so working by the open door of the garage is a bit character buildng!
This started off as a big7, now it’s a Chromidium nippy block.Different kettle of fish altogether and much easier to deal with as you can take the block off and send it to one of a number of well qualified enginers on this forum.
I certaily woul not be having seat insrts put in this block as it leaves very little margin and if Chromidium is even rarer than a Nippy engine.
Top skim to narrow the seats a bit, and very light recut.Slightly larger valves are preferable to seat inserts.
You don’t need hardened seats for unleaded, it’ a fallicy.
I probably wouln’t use this engine without a Phoenix crank for fear of something going wrong.
