Piston to valve clearance

[jay c]

Can anyone advise what is the absolute minimum piston to valve clearance I can safely run. Fitting some new Tims stage 2 heads and checked the clearance and it’s 1mm. I know I could fit a barrel shim but I don’t really want to drop my CR too much(currently 10.5:1). It’s the same clearance as on my previous heads but I never really took the revs over 5500rpm. Have I just been lucky to get away with it or is that clearance just about ok.
Any help would be appreciated
Jay

[Garrick Clark]

My opinion is its a bit tight. Mine was tight like your is , do you have valve pockets. I just stripped the heads, fitted a valve with a cut mark on the valve face NO SPRINGS ETC , refit the heads and spun the valves slowly with a drill and pressed on the drill lightly so the valve head goes into the crown of the piston top.Position piston at TDC . Measure the VALVE LENGTH from the guide to the end of the valve. Spin the valve into the crown a mm. Then you will be safe.
I USED VASELINE ON THE VALVE HEAD TO CATCH THE BITS OF SWARF
CLEAN UP AFTERWARDS.

[richie]

Jay

at what point is it only 1mm? as tdc is not closest place normally, I do think thats a little on tight side all though reality is it will be more than that as engine warms up lash grows so valve doesn't actually get quite as close as cold

cheers Richie

[Garrick Clark]

The Tdc is only to cut the crowns

[jay c]

Had a dial gauge on the retainer (with a lightweight spring) and checked when the valve was open at full lift. Then pressed the valve down by hand until it touched the piston while looking at the dial gauge

[jay c]

Also should mention I have a raptor cam as I’ve heard they allow a slightly smaller clearance and lighter aluminium JPM pushrods and titanium retainers as weight might come into the equation

[Garrick Clark]

Well I say get more clearance so your not thinking about it when it's running. I have a real tight deck height. I'm always wondering is the piston slightly kissing the head

[richie]

Had a dial gauge on the retainer (with a lightweight spring) and checked when the valve was open at full lift. Then pressed the valve down by hand until it touched the piston while looking at the dial gauge

I use the adjuster screw to check the clearance, by winding it in a full lift until valve touches it gives a more exact measurement. If i got 0.060 then its got enough, your aluminium pushrods actual make it slightly worse in this situation as they wont give as much lash as chromoly so it stays tighter which is good for performance and valve train noise but not for clearance .

[richie]

Also you need to roll engine over all the way as its usually just before and after tdc that it get closest, its not actually at full lift.

[richie]

Well I say get more clearance so your not thinking about it when it's running. I have a real tight deck height. I'm always wondering is the piston slightly kissing the head

Yes if it is only 1mm then it needs more, if your deck is less than 0.8mm then it is most likely marking head

[jay c]

Thanks Richie. I’ll check that out tomorrow and let you know. Doesn’t sound too promising but I’ll check and take it from there. Cheers

[Dougy Dee]

Why not use Play-Doh or equivalent on the top of the cyl's, reinstall heads rockers etc, and rotate the engine through a cycle?

[jay c]

Why not use Play-Doh or equivalent on the top of the cyl's, reinstall heads rockers etc, and rotate the engine through a cycle?

i would of but I don’t have any. I’m on total lockdown for 12 weeks so can’t get to a shop to buy any. Not even any blu-tack around the flat.

[jay c]

Well the results were not good Richie. Before tdc the clearance is much less. 0.010”thou exhaust and 0 inlet ( must just be kissing as it turns over easily).  Have to wait until the quarantine is over before I can get anything done about it. Would you know who near east London could perhaps cut pockets into the pistons if that the correct route. Thought changing my heads would be a nice easy job while on lockdown😢

[Garrick Clark]

You could order 2 valves and do it yourself. The lock down might be a long way off yet.

[richie]

Well the results were not good Richie. Before tdc the clearance is much less. 0.010”thou exhaust and 0 inlet ( must just be kissing as it turns over easily).  Have to wait until the quarantine is over before I can get anything done about it. Would you know who near east London could perhaps cut pockets into the pistons if that the correct route. Thought changing my heads would be a nice easy job while on lockdown😢

Do you have access to an old valve at all? easiest way to mark center of valve in piston so they know where to cut pocket is sharpen an old valve to a point and use it like a punch to mark piston by inserting it down guide hole, you will need to remove the valves 1st if you can't get access to an old valve but can remove your valves from head i can post you a cut down valve to use

cheers Richie

[jay c]

You could order 2 valves and do it yourself. The lock down might be a long way off yet.

im just a bit worried that I would mess it up Garrick. I know it’s not overly difficult but one mistake can be costly

[jay c]

Just looked through all my bits and I don’t have any valves Richie. Not sure why I have so many old cam followers lol.
No problem in removing valves. Took 2 out yesterday to fit  my checking springs but no spare valves. If you have an old one that would be fantastic. Really appreciate the help

[Garrick Clark]

It's not difficult honest. I've also in the past stuck some emery cloth to the face of good valves and spun them using a drill. The emery sands a semi circle on the piston top. Keep going till 1 mm or the measurement that you need happens

[richie]

Just looked through all my bits and I don’t have any valves Richie. Not sure why I have so many old cam followers lol.
No problem in removing valves. Took 2 out yesterday to fit  my checking springs but no spare valves. If you have an old one that would be fantastic. Really appreciate the help

Ok will dig one out, am sure we have address but can you send it to Jo just in case please? 

Once you marked it you should be able to find someone to cut them easy enough, you just tell them how deep you want it to be

[jay c]

Thanks man. I’ll message Jo now. Should  .060”thou be enough or a little extra for comfort.

[richie]

Thanks man. I’ll message Jo now. Should  .060”thou be enough or a little extra for comfort.

Got it   I would do more as you can, it will make such a tiny difference to CR might as well be safe so I would do 0.080/0.100 intake to exhaust

[DaveN]

I think the valve hits the head at a angle too. You will need to know this angle so the piston can be set to it before machining.

[jay c]

Cheers Dave. I can measure that. Or find a Vw machinist

[DaveN]

I’m sure afew on here know what the angle is, I think it’s 9 degrees but I’m not sure.  You  can probably find it somewhere on the Internet, it’s been years since I’ve notched any pistons

[richie]

I’m sure afew on here know what the angle is, I think it’s 9 degrees but I’m not sure.  You  can probably find it somewhere on the Internet, it’s been years since I’ve notched any pistons

I thought it was 7 but I always get someone who does it all the time to do it so i could be wrong

[JIMP]

Hello

the angle is 9 or 9.5 degrees, cant recall exactly, but if its for cutting the notches you cant be wrong, be 9 or 9,5 will do your job, also be aware as its said before, the tighest point isnt at full lift, you have to check at about 10o , you will see that actually valve is going back to its seat and the piston goes like "faster" to hit it, there you have to check for your clearance. we have done 2 seasons of rally in an engine running stock internals -even stock rod bolts- and going up to 6500 with a clearance to the inlet of 1mm and exhaust 1,2mm, never had problems or signs of contact after dismantling BUT everything has to be working perfectly to keep clearances that tight, I would recomend though to go bigger for your engine, no reason actually to go that tight

Friendly

Dimitrios

[jay c]

Thanks for the info Dimitrios. 

[Martin S.]

The 1776 I have in the 65 was built with the too-tight deck, and what’s interesting is that you can hear the pistons hit only when the motor is dead cold, then the noise goes away as soon as it starts running and warms up. It’s so close that when the piston heats up, it expands and runs straighter in the bore, causing it not to hit.

[richie]

The 1776 I have in the 65 was built with the too-tight deck, and what’s interesting is that you can hear the pistons hit only when the motor is dead cold, then the noise goes away as soon as it starts running and warms up. It’s so close that when the piston heats up, it expands and runs straighter in the bore, causing it not to hit.

So its not the engine expands as it gets hot and the head moves further away then? hence why there is more lash with chromoly pushrods hot as they don't expand as much