Alphabettispaghetti
Club Member
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Has anyone got pics of large valves installed?
- Thread starter Alphabettispaghetti
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Alphabettispaghetti
Club Member
45/36.5
Alphabettispaghetti
Club Member
They look slightly proud to me, however i'm going to get one lapped in, some engineers blue and look at the interface.
Alphabettispaghetti
Club Member
They're new seats, I think when ground they'll drop a bit, then check with blue, just how much they'll drop against other none standard setup.
Ian Patmore
Well-Known Forum User
Valves are always a little proud. Lapping is only for getting them to sit nicely, and won't take a lot of the seat away.
Maybe an idea to measure installed height of the stem, so when the rocker assembly is added, the lash pads are nearer to the same thickness. I had a head done with new valves, and every valve required a different lash pad (some with quite a size difference).
Then you are onto ccing the combustion chamber?
Maybe an idea to measure installed height of the stem, so when the rocker assembly is added, the lash pads are nearer to the same thickness. I had a head done with new valves, and every valve required a different lash pad (some with quite a size difference).
Then you are onto ccing the combustion chamber?
Alphabettispaghetti
Club Member
Yes, I do think the larger valves seat needs to be 1mm bigger. It does need building up to check the stem height, unbuilt it will get 90% of the way there.
I'll build up the bottom end to triple check the pistons sit exactly where they should be based on the math/measurements, I'll then CC head to see where it needs to be. Hoping to drop the bottom end off for machining in the next week.
Ian Patmore
Well-Known Forum User
So, is the valve seat stock then, and sitting with larger valves? I thought larger valves need larger seats, as the valve then isn't the restricting factor..?
richiep
Club Member
I don't think that's always the case; somewhere in my collection of fun bits for L-gata engines, I've got a set of Japanese valves (can't remember who by) that are meant to be the largest you can use with stock L28-size seats - I think they are 45/36.5mm as opposed to the standard 44/35. This compares to the typical full race/big valve sets of 46/38.
Ian Patmore
Well-Known Forum User
Like I said, ideally valve size goes with seat size. There are pictures of siamized (spelling) valve seats in the how to performance biuld your L gata, showing this, larger valve seats, where the valve seats merge together, with no aluminium between them (as per stock). If not, the larger valve will sit more proud than stock, what that does for swirl patterns/fuel/gases in and out, who knows. Valve lapping is meant to bed the valve and seat together, not to lap the seat down in the hope of fitting a oversize valve, as the contact surface will be further up the valve underside, nearer the stem. Then you have an "overhang".
All a bit pointless unless the valve guide is properly machined for flow (and not necessarily machine "flat" to the cylinder head port ceiling) and a good multi angle valve grind for efficient flow out/in of the valve seat and the cylinder head is properly worked for max cfm.
All a bit pointless unless the valve guide is properly machined for flow (and not necessarily machine "flat" to the cylinder head port ceiling) and a good multi angle valve grind for efficient flow out/in of the valve seat and the cylinder head is properly worked for max cfm.