Head work on my Sprint

[73sprint]

I am doing a good head for my Sprint. I have had new valve guides fitted and the valve seats re cut to accept 16 new valves. However the inlet clearences are virtually ziltch. I have fitted 0.093 etc and got no clearences.
I know i can get some Lotus 907 shims that start from 0.060 etc.If i need to fit some say in the 0.075 range upwards will this cause any problems ?. Will the buckets still clear the valvespring collers ?. Thanks in advance

[soe8m]

Redo the head work. It's no use. The next time you don't have shims anymore. These thin shims will cause the valves pop loose. Accept the head is not good and start all over instead of bodge jobs and have more damage over some time.

Jeroen

[Carledo]

I would guess that too much meat has been removed from the valve seats. So the head is not scrap, but may need some new seats fitting.

Steve

[73sprint]

Oh no. Is it possible to have the inlet valves ground down by the engineering company ?

[soe8m]

Oh no. Is it possible to have the inlet valves ground down by the engineering company ?

What would be the benefit of that?

Jeroen.

[tony g]

Yes grind the valve tips a little to get each one in the range youd like. Its common practice on a lot of engines. Obviously the tip of the valve protruding through the retainer must be enough so that if the shim rocks a little bit it wont contact the collets, thats disaster.
When I had a 3 angle valve cut done on my sprint the v clearances were too small too. I fitted a reground cam (smaller base circle) which normally requires much thicker shims but and selected the shims from my tin so happy days . If youre thinking of a reground cam as an upgrade I'd do it now and you may get lucky with the clearances.

Tony

[soe8m]

No way. The only effect is you can fit thicker shims. The buckets will still push the spring seat thus loosening the valve. Redo the head only option.

Jeroen.

[tony g]

Buckets pushing the valve retainer? How?

Tony

[soe8m]

I feel a drawing. Wait for it.

[soe8m]

At first, valves what are too high in the head do also have too much valve spring length. So for performance the right position is importand.

Drawing 1 is a normal situation. The bucket does push on the shim and the shim on the valvestem. A direct contact and the only action is valve open.

Drawing 2 is the situation that 73sprint and Tony have. The valve is too high in the head causing to less play and no shims available. Using too thin shims, not designed for the dolomite engine this situation the bucket can push the upper valve spring seat what causes loosening the valve first and then opening. This is a situation that you do not want and can cause serious engine damage when a valve comes loose.

Drawing 3 is the repair Tony suggested. The only thing what happens is that you can fit a thicker shim what is available but for the rest nothing changes. The bucket to spring seat distance does not change and will never change. You only change the way how you adjust the too narrow valve play what is caused by wrong or too much machined seats. The distance seat/camshaft will never change, whatever you do.

Drawing 4 is a too much machined valve stem. The shim rests on the seat. This way the valve is pushed loose first also before opening. A different way but the same catastophic effect.

As you can see the only way is to have new seats fitted.

Jeroen

Scan_20160719 (2).jpg (9.89 KiB) Viewed 1161 times

[tony g]

That all depends on how much clearance is ACTUALLY between the bucket and retainer before you start. My method with normal shims and reground cam has been very good for 2000 street miles driving hard but not 7000 rpm ( well maybe once). Agree to disagree on this as specific set ups will vary. There is no 2 engines the same really

Tony

[soe8m]

You may disagree but it would not be wise. The thinnest shim has a thickness that the inside of the bucket will never tough the spring seat. Start using thinner than the thinnest std dolomite shim can cause parts touching each other what is undesirable. Grinding the valve stem to use available shims again is fooling yourself. Too much wear is too much wear.

Tony you use a regrind cam and therefore created more play towards the camshaft so you can use normal shims again what does raise the bucket from the upper valve seat. Still not perfect but it is 100% safe. As long the bucket to seat distance is okay.

Jeroen

[tony g]

Mine is more perfect than having big thick shims waiting to jump out at high rpm. When using ground valves retainer to bucket has to be checked of course

Tony

[soe8m]

More perfect for a reground camshaft but valves up high in the head do miss a lot of flow advantage. A valve on top of a valve seat opening 9mm is open 9mm. A recessed valve in a valve seat that has to overcome 2mm out of a tunnel does has an effective 7mm valve lift/opening. The "open" area around the valve is greatly reduced. So not so perfect.

Jeroen

[73sprint]

Thankyou for yur input. Thats what concerned me, the buckets contacting the valve collers. But why are the exhaust clearences fine as the work was done all at once by a good engine recon company?. I will give them a
call and take it from there.