machining shims

Here are a couple of bits of info that may help or at least provide somewhere to start.

Hi there!

That's a fairly well known procedure in modified engines with no other provision for shimming up. I used to make dozens of them for our Slick 50 Golf Gti engines. It allowed the use of a lighter cam follower and removed the possibility of the std follower spitting a shim out at high rpm (the std followers have the shim on top rather than underneath in that engine).

Any decent quality hardenable steel will do. I used to use old main bearing cap bolts from scrap engines which are high tensile and hardened nicely with a heat and quench without ending up too brittle. Silver steel would do at a pinch if it's tempered back a bit from the very hard condition.

The other method is to make special valve spring caps with a recess on top to hold the shim like the Peugeot 205 engines use as std. Then you can just buy the Peugeot shims which are available in 0.05mm increments. Saves the grief of grinding shims down to thickness to set the valve clearances on every engine build but costs more to start with of course.

If you get stuck for someone to do it you can email me but bear in mind as a one off exercise it's the best part of a day's work and not so cheap. Mind you, still probably cheaper than using someone who doesn't know what they are doing and writing an engine off when it drops a valve :)

Might help if you said what engine it was.

-- Dave Baker - Puma Race Engines

righty, good responses many thanks.

as it happens dave, i am the guy that is going to be buying that set of mi16 inlet recon valves off :-) emailled you a few days ago.

they are to be fitted to an F7P renault engine, which is a 1764cc 16v. std valve size is 30mm, with other std variations of 32mm and up to

33m, so the 34.6mm of the mi16 would hopefully be a nice non-std upgrade.

(side note - do u think the exhausts would need upping? they are 28mm?)

ok, the mi16 valves sit 1mm shorter than the std renault ones. the engine runs hydraulic tappets, but after some drawing, worked out that the std tappets will not have enough adjustment left in them to compensate for this, hence the need for some sort of shim/cap to take up the extra 1mm that has been introduced.

well, a std cam would be ok, but its quite likely a regrind would want to be used, which would not work...

my initial thoughts were some sort of cap, made from said steel, which could be a slight press fit onto the end of the plunger on the tappet, the part that makes contact with the valve stem...when i say press fit i only mean press-by-hand...enough so it doesnt fall off during assembly.

this of course is just an initial thought and id be happy to hear better thoughts...its just that there is no provision for shimming as they were never designed to take them.

many thanks for your time,

Jon

They'll be ok. Very little gain from fitting larger exhaust valves to anything.

I'd be very surprised if a hydraulic tappet didn't have at least 1mm of extra play in it. OE tolerances aren't made that close.

Lash caps are usually made to fit on the end of the valve stem rather than the plunger of the tappet.

You should always quote what you are replying to on usenet or people can't follow the conversation.

I'll be checking out those Mi16 valves later today hopefully.

-- Dave Baker - Puma Race Engines

hmm i would like to quote if i knew how...(i just view this on the web, not in an email client)

basically the tappet has about 2.5mm of play, in std form, ie using std cams, about 1.5mm of this is taken up leaving about 1mm left of compression into the tappet.

now that 1mm thats left is pretty much all taken up by the fact that the mi16 valve sits about 1mm lower...and then if u put regrinds in which could have up to 1mm ground off, then we've run out of play...they will rattle up to 1mm.

i prefer ur idea of fitting the cap to the valve, makes more sense. this will mean that the spring cap would need to be machined down a little as the stem only protrudes about 1mm above it...but thats do-able.

another factor is that the springs are apparently under 1mm less compression, this would need shimming too i think.

Jon