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Lars S
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Joined: October 04, 2007
Posts: 786
Location: Sweden
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 Posted: Fri Nov 07, 2014 10:58 pm Post subject: 1.7 D-jet, largest valve clearance NOT at TDC!? |
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Dont know i this has been covered before but when I have set the valve clearance on cyl 4 (as an example) at TDC to spec 0.06 (0.15mm) and then turn back the engine ½-turn (i.e. to no1 TDC) the play on no4 exhaust valve has increased to about 0.08 (0.20mm).
I have noticed the same on three different 1.7 engines, two with stock D-jet cams and one with Webcam D-jet cam.
I thought the largest play was at TDC but it seems not to be...anyone have similar experience or an explanation?
/Lars S
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VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
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raygreenwood
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Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Fri Nov 07, 2014 11:29 pm Post subject: |
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Yes, this is normal. I noticed it years ago. This is because the factory TDC valve setting point ia, TDC for the cylinder and the lifter is not at the exact "0" or bottom of the cam lobe base circle. Its just a little way up the flank of the lobe from the bottom of the base circle.
There is one way to look at this.....the factory wanted you to see .006" at that specific point as a safety margin.
The difference is to see what that extra lash changes to when the engine is hot and at the very bottom of the base circle.
I found quite a few years back that D-jet runs smoother, has a less choppy vacuum signature.....with slightly tighter valve settings. I set them at the normal TDC points.....hot......at about .002"-.0025". That equals about .006"-.007" at actual bottom of the base circle. The car runs and tunes better and is more quiet.
This has given me no problems.
As long as there is adequate clearance within the cam lobe circumference at valve closed and maximum hot condition there is no worries. Ray |
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Lars S
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Joined: October 04, 2007
Posts: 786
Location: Sweden
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| Posted: Sat Nov 08, 2014 1:56 am Post subject: |
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Thanks Ray!
Glad you knew about this, wery little seems to be written about it.
I also like setting the valves tight at TDC...abut 0.05 for the same reasons as You...as soon as a valve is back to 0.06 I can hear it.
As you know a lot of people like to set the valves to spec 0.06 at not TDC and I guess the factory safety margin will allow for this, at TDC their clearance might be tighter but not to tight ( if they not set them wery tight when they are off TDC).
Lars S
_________________
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Sat Nov 08, 2014 7:57 am Post subject: |
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| Lars S wrote: |
Thanks Ray!
Glad you knew about this, wery little seems to be written about it.
I also like setting the valves tight at TDC...abut 0.05 for the same reasons as You...as soon as a valve is back to 0.06 I can hear it.
As you know a lot of people like to set the valves to spec 0.06 at not TDC and I guess the factory safety margin will allow for this, at TDC their clearance might be tighter but not to tight ( if they not set them wery tight when they are off TDC).
Lars S |
Yes, one thing I am doing over the next couple of months when I build my engjne.....I, am fully degree-ing the fan so I can know exactly where I am setting the valves up on the ramps of the lobes and by degree on the fan. I will map this during mock up.
Yes.....when I set my valves cold at normal TDC....I set then typically to .0045"-.005". I check when hot at standard TDC and the valves are then .002"-.0025".
Knowing how to set them that way which we know is perfectly safe...I want to then put the engine in position at the absolute "0" of the base circle at that adjustment......and then measure what the real gap is at real lowest, base circle. Also to find in degrees on the fan ring....where the "0" of the base circle begins and ends.
The cam I have is a Raby 9550. If I could find an old actual stock 1.7l d-jet cam I would map that also....just ao others have some baselind for better adjustment. Ray |
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Lars S
Samba Member
Joined: October 04, 2007
Posts: 786
Location: Sweden
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| Posted: Sat Nov 08, 2014 8:15 am Post subject: |
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OK Ray,
do you think cam wear could affect the relationship clearance TDC/Not TDC, I mean if an old used cam could be different in that way than a new.
Also have you found a way to use a dial clock to set the valve clearance? I think that would be more accurate than the feeler gauge (which I wear down quickly when setting clearances tight)
Lars S
_________________
Porsche 914 -72, Bahia Red daily driver
VW411 2-d -70, White, sold
VW412 4-d, -73, Gold Metallic, daily driver
Suzuki T500, -69, Candy Gold, sold
Suzuki K50, -77, Black, daily driver
BMW R69S -69, White, sold
Husqvarna 118cc, -47, Black, Sold |
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raygreenwood
Samba Member
Joined: November 24, 2008
Posts: 21520
Location: Oklahoma City
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| Posted: Sat Nov 08, 2014 9:57 am Post subject: |
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| Lars S wrote: |
OK Ray,
do you think cam wear could affect the relationship clearance TDC/Not TDC, I mean if an old used cam could be different in that way than a new.
Also have you found a way to use a dial clock to set the valve clearance? I think that would be more accurate than the feeler gauge (which I wear down quickly when setting clearances tight)
Lars S |
As to the wear issue.....I have only found in my experience that unless you have really serious wear issues from cam/lifter metallurgy or oil issues....meaning really short life (flat cam syndrome).......there is virtually no wear in the flank area where you check valve lash because spring pressure and speed of lifter movement is at Its lowest.
I have done some checking with a dial indicator ......but its very hard to mount quickly and easily.
I usially use 2-3 feeler gauges of each thickness when checking hot so I cancuse them once and let them cool before using them again. Ray |
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