Track Sprint Resto

[DoloWIGHTY]

They look thicker too?

[soe8m]

Are you sure about the valveseats? They look they have way too much valve contact.

Jeroen

[Mad Mart]

Are you sure about the valveseats? They look they have way too much valve contact.

Jeroen

Can you explain further Jeroen?

[Mad Mart]

They look thicker too?

You have a keen eye Alan. The old ones are 4.1mm. dia. but the new ones are 4.25mm.

[Mad Mart]

Having consulted the Sprint repair operations manual, the free length (approx.) of the valve spring should be 40.64mm. (1.6"). The old ones are only a smidgen less than this at 40.45mm., whereas the new ones are 42.3mm.. I've just dug out my old uprated springs (covered less than 1000 miles I would guess). They are a similar length to the old springs. Don't think I should use these new valve springs?

[DF]

Are you sure about the valveseats? They look they have way too much valve contact.

Jeroen

Can you explain further Jeroen?

Im sure he means the seats haven't been trimmed back for better flow
They do seem quite large for a performance engine,
Some people get 3 angle valve seats cut and u usually end up with
About 1mm valve to seat contact slightly more on the exhaust as it helps cooling of the
Valve, inlets are cooled by the fuel
Hope this is what he means

[Mad Mart]

I see. I do go a bit mad with lapping the valves in.

[DF]

Having consulted the Sprint repair operations manual, the free length (approx.) of the valve spring should be 40.64mm. (1.6"). The old ones are only a smidgen less than this at 40.45mm., whereas the new ones are 42.3mm.. I've just dug out my old uprated springs (covered less than 1000 miles I would guess). They are a similar length to the old springs. Don't think I should use these new valve springs?

If u do use the new springs they' need checking for coil binding at full lift
Depending on what cam your running
I would also check the poundage at full lift
Don't know what revs you use but doubles wouldn't go a miss .
Bit more expensive I know

[soe8m]

Hello Mart,

Double springs are not needed for a sprint, not even with a high lift cam. Std springs do fine and do less stress the lobes and the chain.

Darren did explain what i did mean. For my new LPG project i did some calculations what the most ideal seat/valve contact was because the LPG has a higher temp combustion and the valves have to have more contact area because of the cooling.
For LPG my sprint has 2mm contact for the exhaust and 1,5mm for the inlet. Too less will burn the valve but does have a good sealing. Too much will cool very good but the pressure per square mm is less so will seal less, contaminate more and will burn also the valve. This is in your case and i think it will not last very long.

For a normal petrol sprint the inlet has to be 1mm and the exhaust 1,5mm. This is the most ideal. You only will get this by 3 angle cutting. You have one steep angle behind the valve and a low angle in the combustion chamber side. By controlled machining you can machine these two angles till you have reached the desired contact angle. The other thing is you will also have a better flow. But this is not why you have to choose for 3 angle cutting. The main reason is there's no other way to create a desired contact area.

Jeroen

scannen0002.jpg (137.74 KiB) Viewed 5560 times

[Mad Mart]

Thanks Darren, I decided not to use the new springs or my uprated ones.

Thanks Jeroen, I knew about the 3 angled valve seats. Bodgerben gave me all the info I needed a while back. But it looks like I've gone too far with my valve lapping. I have some new seats and valve guides so I may take the head to my local machine shop to get it sorted.

[Mad Mart]

I found a machine shop fairly local to me, in Bridgwater.

http://www.hamlinsengineering.co.uk/

I spent an hour with their head guy (head guy, get it? ) this afternoon and apart from one worn valve guide and a couple of dodgy valves, all is well. So I'm getting a 3 angle cut on the seats and a new valve guide (which I provided).


On the way back I popped into the body shop to drop some trim off to Jon. Took a couple of pics with my mobly whilst I was there.

[Mad Mart]

I spent a bit of time this morning cleaning up the block & running a tap down some of the threads. I also cleaned up the lightened flywheel I bought from Alun a couple of years ago. It came up quite nice. It's not been lightened too much. Std flywheel weighs 9.6 kgs whereas my lightened one weighs 7.8 kgs.

You can see on the front that just a large chamfer has been removed around the edge...



...and on the rear a large scallop has been removed from the middle...



Looking at the old flywheel on the right I noticed that there is no wear on the front face where the friction plate bites, so I wonder if it's a new one or has been faced off?


I need to remove the pins that locate the clutch plate from another flywheel to transfer to the lightened one, I tried a bit of heat & some pliers but I just started to damage the pin. Anyone removed these before?

[DF]

Heat wd40 and some mole grips
That's what worked for me
Or pilot hole behind And knock them out .???

[Mad Mart]

No luck with that Darren.


I picked my head up from the machine shop yesterday. Looks very nice.





Thanks for pointing it out Jeroen else I would have just put it back together as was.

[soe8m]

My head will be ready in about two weeks. Only the valves have to be shortened because i want to start with the thickest tappet shims possible because of longlivety on LPG. Will put some pictures in my new project thread soon.

For valve saving i did buy an programmable automatic pump device whats running together with fuel injection. The valve saver bla bla with the vacuum hose isn't working. The most vacuum at idle and the least under load so the fluid is at least when the most needed. The device i bought does not work at vacuum but has a pump which does pump more fluid when there's more LPG injected so i hope this new engine does last more than my old one. That one did about 270.000km on LPG without any valve saver devices so i'm now aiming at 350.000km at least.

On your head i see some skimming possibilities for more compressio ratio and more power. The seats look ok.

Jeroen