I am currently assembling my twin spark head with custom valves, custom guides, performance springs, and 11.6 mm lift cams.
Before my final assembly I have checked the spring retainer to valve guide clearance at 11.6mm valve lift.
The exhaust retainer to guide clearance is 2.5mm (no valve seals) OK.
The inlet retainer to vlave guide seal is 0.5mm NOT OK. There is 4.4 mm clearance without the seal.
I cannot shorten the inlet guide any further. My only option is to machine some material from the bottom of the retainer, or assemble the valve train without valve stem seals.
Considering the alfa engines cam followers act as an umbrella to oil and there are many engines out there that don't use valve stem seals I feel this should not be a problem.
What do engine builders do when alfa heads are fitted with 13mm lift cams?
What is the recommended minimum valve retainer to guide/seal clearance?
Thanks,
Dom.
I don't have the problem with 13mm, but I propably have different valve length than you have.
TS_turbo told the easy way to increace the clearance. If you're retainer to valve seal clearance is now 0.5mm, it only needs to drop guides by another 0.5mm to get safe 1.0mm. That's one solution.
As the seals are made of flexible rubber, I could dare to try even that 0.5mm.. 1mm is better anyway, of course..
TS_turbo told the easy way to increace the clearance. If you're retainer to valve seal clearance is now 0.5mm, it only needs to drop guides by another 0.5mm to get safe 1.0mm. That's one solution.
As the seals are made of flexible rubber, I could dare to try even that 0.5mm.. 1mm is better anyway, of course..
Kimmo / alfatune.fi
1. is the valve seal seated completely on the inlet side? if there is a small gap between the top inside of the valve seal and the top of the guide, maybe you can trim some off the bottom of the seal?
2. perhaps you can machine a small groove around the guide to countersink the seal base .5 to 1.0mm?
3. is there a thinner topped valve seal?...my vitons with the wrap around spring are at least 3-4mm tall above the guide....
2. perhaps you can machine a small groove around the guide to countersink the seal base .5 to 1.0mm?
3. is there a thinner topped valve seal?...my vitons with the wrap around spring are at least 3-4mm tall above the guide....
Thanks everyone for the suggestions.
x-rad I have found the Alfa OEM black seals with spring are shorter again at 9.3mm high, a gain of another 0.2mm. Also I will machine another 0.6mm from the bottom of the spring retainers which will give me 1.3mm clearance.
TS_turbo Unfortunantly I cannot move the guides down the bore any further as I are using Mercedes guides which have a wire ring around the guide which locates and stops the guide from moving down in the head.
After some internet search most spring/cam manufacturers say minimum clearance for American iron V8's 1.5-2.5mm, for 16 valve rice burners 0.75mm, and for Harley Davidsons 0.5mm.
In reality the Alfa engine with no rockers and lightweight cam followers and adequate spring tension should not have the problem of the valve departing from following the cam lobe so anything over 1 mm should be adequate. As kterkkila describes at worst if there is contact with the retainer and seal it soft and should not cause any danger.
x-rad I have found the Alfa OEM black seals with spring are shorter again at 9.3mm high, a gain of another 0.2mm. Also I will machine another 0.6mm from the bottom of the spring retainers which will give me 1.3mm clearance.
TS_turbo Unfortunantly I cannot move the guides down the bore any further as I are using Mercedes guides which have a wire ring around the guide which locates and stops the guide from moving down in the head.
After some internet search most spring/cam manufacturers say minimum clearance for American iron V8's 1.5-2.5mm, for 16 valve rice burners 0.75mm, and for Harley Davidsons 0.5mm.
In reality the Alfa engine with no rockers and lightweight cam followers and adequate spring tension should not have the problem of the valve departing from following the cam lobe so anything over 1 mm should be adequate. As kterkkila describes at worst if there is contact with the retainer and seal it soft and should not cause any danger.