Cam timing, decked and skimmed head

[ben_p]

My engine is currently being timed up, they said they cant run it on stock timing as the head had to be skimmed and they decked the block to bring the clearance up..

How would they do this as the cam cover is holding the cams down and you cant get to the lobes, its on standard pulleys.

Would they have to drill a hole in the cover to time it?

 

[2 live]

surely if theyv done the work.....theyl know how to finish what they started......and will have taken care of any clearance issues before they started??

 

[Hutchie]

erm.... the pistons need tickling with a milling machine, is what it sounds like to me, ohhh and dont let them near your engine again sound like cowboys

 

[.GAZ.]

FFS!

 

[sideways danny]

I think what they're refering to is the change you would see on a keyway'd engine. This would ordinarily throw the cam timing our by a notable amount. That's the huge advantage of fully floating engines, you get the timing events in the right place no matter what the deck height.

That's of course unless they've taken too much off and you're getting valve/piston contact

 

[Hutchie]

i was of the idea that with both timing locking tools in its the best it can be in the case of avoiding the piston and valves hitting

 

[sideways danny]

i was of the idea that with both timing locking tools in its the best it can be in the case of avoiding the piston and valves hitting

no

With Cat 422s the inlet valves are open at TDC by more than stock (other cams do too, but 422s a lot more) You have to check very carefully to make sure there's always clearance

 

[Hutchie]

no

With Cat 422s the inlet valves are open at TDC by more than stock (other cams do too, but 422s a lot more) You have to check very carefully to make sure there's always clearance

set cams to tdc and piston to tdc, putty ontop of piston rest head on and wind down to measure clearance????

 

[sideways danny]

yeah use playdough, i'd lock the cams then bring the pistons up to TDC myself. I find a borescope is incredibly usefull too

 

[Hutchie]

yeah use playdough, i'd lock the cams then bring the pistons up to TDC myself. I find a borescope is incredibly usefull too

good point

 

[Andrew Cooke]

yeah use playdough, i'd lock the cams then bring the pistons up to TDC myself. I find a borescope is incredibly usefull too

how much valve clearance do you allow? Piston to valve contact won't be at TDC. On my engine there is 0.5mm less piston to valve clearance at 8 deg than at TDC.

 

[sideways danny]

I try to allow 1mm minimum. Time up and run through from around 25deg BTDC to 25deg ATDC then check the playdough. The worst point for contact I've seen is the edge of the valve cut-out on the inlet side, but that varies by piston manufacturer. We tend to avoid block skimming if possible TBH

 

[Hutchie]

I try to allow 1mm minimum. Time up and run through from around 25deg BTDC to 25deg ATDC then check the playdough. The worst point for contact I've seen is the edge of the valve cut-out on the inlet side, but that varies by piston manufacturer. We tend to avoid block skimming if possible TBH

only causes problems decking imo

 

[ben_p]

WOW WOW WOW, They havent asked me to find out! they are very experienced time served aston martin engine builders! I was just asking how they do it! They have checked all the clearances on a dry build and it does not clash on standard timing. What they were saying was that there is more power to be had than just to leave it on OEM timing when the clearance has been brought up etc! they know what they are doing lol! I was just wondering how they do it as im always asking questions to them and didnt want to waste his time trying to explain it to me!

 

[ben_p]

The clearance is really tight on it, something in the low thou's with no gasket on the 25 degrees before and after. He spent ages doing it, gapping the rings etc!