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post #1 of 22 (permalink) Old 02-23-2014, 10:07 AM Thread Starter
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Piston to Valve Clearance

Hello All,

1991 Spider Veloce.

I am in the middle of an engine build.

I installed 10.4:1 motronic pistons and had the head shaved 0.020 plus the head was shaved 0.008 previously.

New valve guides, seals, springs but original valves.

So I wanted to make sure there werent any interferene issues with the new pistons and valves.

I used the play dough method.
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Rotated the engine over 2X
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Cut and measured the play dough.
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I admit that the measurement is not super accurate but its close enough.

Here are the results:

1 2 3 4
Intake 0.208 0.190 0.192 0.116
Exhaust 0.120 0.125 0.130 0.115

So, my question.

Why do you think that #4 is so much tighter than the others and what would cause this?

Thank you,

Vin

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #2 of 22 (permalink) Old 02-23-2014, 10:49 AM
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Quote:
Originally Posted by Vintre View Post
Hello All,

1991 Spider Veloce.

I am in the middle of an engine build.

I installed 10.4:1 motronic pistons and had the head shaved 0.020 plus the head was shaved 0.008 previously.

New valve guides, seals, springs but original valves.

So I wanted to make sure there werent any interferene issues with the new pistons and valves.

I used the play dough method.
Attachment 468345

Rotated the engine over 2X
Attachment 468353

Cut and measured the play dough.
Attachment 468369
Attachment 468377

I admit that the measurement is not super accurate but its close enough.

Here are the results:

1 2 3 4
Intake 0.208 0.190 0.192 0.116
Exhaust 0.120 0.125 0.130 0.115

So, my question.

Why do you think that #4 is so much tighter than the others and what would cause this?

Thank you,

Vin
just what it implies... either the valve is sticking up in the head much higher or the valve relief in the piston is cut differently. have you cc'ed the domes to see if they are the same ?
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post #3 of 22 (permalink) Old 02-23-2014, 10:54 AM Thread Starter
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Originally Posted by stevesxm View Post
either the valve is sticking up in the head much higher or the valve relief in the piston is cut differently. have you cc'ed the domes to see if they are the same ?
stevesxm,

Thanks.

How do I cc the domes (or what that even means) or check the height of the valves in the head?

Thanks for the learning.

Vin

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #4 of 22 (permalink) Old 02-23-2014, 11:10 AM
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stevesxm,

Thanks.

How do I cc the domes (or what that even means) or check the height of the valves in the head?

Thanks for the learning.

Vin
you use the same equipment you use for ccing the head except that for the domes, you run the piston down into the bore until the highest point is dead even with the top of the bore. you just lay a straight edge across the bore and run it up until it just touches...

then you seal the piston with a little grease (or you wipe a little grease in the bore first roughly where the rings will be and move the piston into it as you come up....)

then you fill the volume with measured fluid from a buerette ... that gives you a volume of that space minus the volume of the dome. and thats your answer. the volume of an empty cylinder that is that dia and that deep minus what you just measured... thats the dome volume. you do this to make sure that the machine work has been correct and that you actually have 10.5 to 1 instead of 10 .0 or 11.3 and you do this to make sure all the cylinders are the same. if you do this and your dome with the tight clearence is also meaningfully smaller, then that tells you that the valve pocket is probably high. if its the same as the others then look at how deep that valve is sunk into the head vs the others....

and i have to say this even though there will be mass disagreement amongst the hot rodders here, 10.5 to 1 is pressing the issue w/ street fuel these days and if you insist on doing this , then you really have to ignore what they said on the piston box or what anyone else tells you... you must confirm the compression ratio by actual measurement yourself to keep for getting ambushed by an " accidental " 11.3 to 1 or something...

just remember... its your motor and you are the one thats going to have to fix it if you are wrong. not the guys who say " i run 11.5 to one all the time on 87 octane w/ no problems..."
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post #5 of 22 (permalink) Old 02-23-2014, 11:12 AM
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Hi Vince,

can I ask why you used 10.4:1 instead of the standard 10.0:1 motronic "flat crown" pistons?
....I've read sort of 'not so great' reports.....that is why I ask.

http://www.alfabb.com/bb/forums/engi...dvantages.html

But your thread makes me almost want to tear apart my S4........it is all looking too darned shiny-clean

Dom - Alfa Spider 1990 S4 - formerly: Alfa 101 Sprint, 2600 Sprint, Montreal - family classics: Jensen Interceptor II, '58 Hooper RR Silver Cloud I, Shadow II, '60 Corvette.
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post #6 of 22 (permalink) Old 02-23-2014, 11:53 AM Thread Starter
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Hi Dom,

I went with the 10.4's purely for more compression and I hope will translate into some more ooomph!

Here's a comparison with the stock piston on the right (like you couldnt figure that one out! )

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The problems I think are from either clearance with a milled head, which this thread shows I dont have any interferrence issues or with people who are using 87 regular gas.

However, being Motronic, I have always been on the higher octane 91 and do not expect any issues.

Thanks,

Vin

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #7 of 22 (permalink) Old 02-23-2014, 11:55 AM Thread Starter
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steve,

Thanks for the lesson!

Appreciate the knowledge.

Vin

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #8 of 22 (permalink) Old 02-23-2014, 12:01 PM
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Quote:
Originally Posted by Vintre View Post
However, being Motronic, I have always been on the higher octane 91 and do not expect any issues.
Welp, I guess you're gonna find out one way or the other, eh?

Make sure you don't run projected tip spark plugs with those pistons, though.

Tom

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post #9 of 22 (permalink) Old 02-23-2014, 01:39 PM Thread Starter
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Welp, I guess you're gonna find out one way or the other, eh?

Make sure you don't run projected tip spark plugs with those pistons, though.
Ya, I will let you know how I do on the 91 gas.

Projected tip spark plugs? Back into the basement I go!

Vin

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #10 of 22 (permalink) Old 02-23-2014, 02:44 PM
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Projected tip plugs should not interfere with your piston crowns. My Venolia racing pistons have much bigger domes and there is plenty of clearance. I have also used these plugs with 10.4 Borgo's and there were no problems, in fact the motor seemed to run better with them.

Ed Prytherch
79 Spider
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2011 Jaguar XKR

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post #11 of 22 (permalink) Old 02-23-2014, 02:46 PM Thread Starter
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That was fun.

Running Iridium's.

Used the same play dough technique only placed it on the top of the piston. Turned the engine over (Wow! what a difference turning the engine over with spark plugs in!).

The plugs didnt even touch the play dough enough to leave an impression.

Thanks for the heads up.

Vin

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #12 of 22 (permalink) Old 02-23-2014, 03:02 PM
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Measuring P to V distance.

All you are doing is measuring the combustion chanber distances between pistons and valves at TDC.

If you want to know is what the piston to valve clearances are. You have to build the engine with cams, chains setup at the LCs the builder supplied, and roll the engine through the run cycle.

Far easier to follow my instructions with the cam/head to insure that minimum clearances are met.

Here`s the beginners guide:


Camshaft InstallationTiming

First some basics:

YOU MUST CHECK VALVE TO PISTON CLEARANCE BEFORE STARTING MOTOR!!!

Before removing your cams measure the lash on the existing (stock?) cams and record these

The stock cam`s base circle is supposed to be 1.085 inch.(Stock Nord not 91 & later intake) Other cams vary. Measure the base circle with a pair of digital or analog calipers. (Side to side below lobe) and record this info.
With the info above you can estimate closely the shims needed to reset for the new RJR/WebCam lash adjustment. Most of my street camshafts are built to a base circle of 1.050 to 1.065 inch(normally). (And they are exact! All of them) They are built smaller to allow for the typical valve recession done during valve regrind and seat reshaping. But not to the extreme of other builders (C&B base circles are typically 1.020) However, we can build cams to any base circle wanted however.
If you are running a stock Alfa cam with 1.085 base circle and your intake clearance is .016, and the shim is .082 thick and you want to maintain that same clearance with the RJR cams you will need a shim that is .010 thicker, or .092. (Shim increase is ˝ of the difference of the base circle`s
diameter difference.) Ie: RJR`s bc of 1.065, vs. a C&B`s bc of 1.020 = .045 difference. Divide by ˝ = -.023 thinner shim to install the RJR cam. If the C&B was fitted with a .102 shim then a .079 shim would be needed to maintain the same clearance. Add clearance or subtract clearance as needed for your application`s lash measurement..
A final adjustment is usually needed but this will save repeated pulls.
Cams can be pulled without breaking the chain link. Loosen fully & remove cams. Install cams with loose sprockets with no through bolt. By turning motor 1/4 turn at the crankshaft cams can be turned to check clearances without worry of hitting pistons with the valves. Leave chain loose until ready to time the cams.
When cams are adjusted & timing is correct the through bolt should be installed in sprocket and cam nuts tightened using “Locktite” or other thread locker. Refer to factory manual if unfamilar with this type instalation.

Timing Typical Cam with non VVT sprockets:
(after lash settings are finished)

YOU MUST CHECK VALVE TO PISTON CLEARANCE BEFORE STARTING MOTOR!!!

Your timing card will have suggested lobe centers for placement initially. I suggest that if you do not have a timing template for checking the timing marks on your cam caps then download one from Centerlinealfa.com as stock timing marks are all over the place.
Mark cam caps accordingly, and time cams. Hand turn the engine with chain tightened, a couple of turns and check timing positions. Check piston to valve clearance with appropriate plastic wire tie through sparkplug hole on both cams.
Recheck nuts bolts for tightness. Did you use thread locker on cam nut?





VVT Intake Cam installation and timing:
(after lash settings are finished)

YOU MUST CHECK VALVE TO PISTON CLEARANCE BEFORE STARTING MOTOR!!!

I commonly make a secondary timing mark on the camshaft that is highlighted. It is a mark between , appx. 20 crankshaft degrees past the factory mark.(probably red or yellow)
On your intake cam cap make permanent mark at 120 BTDC, 118 BTDC and 102 degreesBTDC.
Initial timing and valve piston check:

This is very important as when cams advance the piston clearance reduces dramatically.
(With chain tight and exhaust cam already timed and checked for piston & valve clearance.)

Set the secondary(yellow) mark I have made on the cam at the 114 / 116 degree mark on the intake cam cap. (for VVT)

This mark places cam in the “advanced” position effectively for checking valve to piston clearance at a LC of 100 or 102 degrees BTDC.
By running the .050 plastic wire-tie between the valve & piston, you can check if there is any interference. If by turning motor over by hand you feel some interferance using a .050 thick wire-tie, but the motor continues to roll through, you are at the limit!
If it locks up, retard the cam a couple of degrees and try again until the clearance is found.
I suggest as a test to find this limit, you advance the cam until you do, and permanently mark that point on the cam cap in line with the yellow cam groove. That will be the point where the cam must NEVER be advanced past.
Move the cam so that the factory timing groove in the cam lines up with the mark made opposite the one made for my “secondary” timing ridge. This should be at or before the 114 degree mark ie” 1148 to 116 BTDC)
Timing initially is dependant on design of cam lobe. Aggressive large duration cams will be more retarded.because of ramp & valve lift.

Tighten and instal lock nut on intake and bolt through sprocket and cam nut. Inspect carefully.
Roll the crankover by hand to verify timing.
When cam is at the limit, or 102 whichever is less advanced. You are there!

MEASURING PISTON TO VALVE CLEARANCE

Intake:
Use a plastic wire tie that is .050(+-)thick. (.040-.060) Cut off the thin leading part and bend slightly about 1 inch from end. The idea is to get the wire tie between the piston & valve as the valve is opening and the piston is moving down from TDC.
If wire tie is too long it might get between valve and the pistons edge of the valve pocket and give a false reading. Repeat the process until you are sure that you are measuring the valve to piston “pocket”.
Adjust to get more clearance by retarding the intake cam.

Exhaust:
This side is critical since the piston is rising towards the closing valve. If valve float happens and there is not enough clearance, something bends, or breaks! Do it carefully!
Using a wire tie that is at least .080 to .100 thick do as above, but any interference will happen between valve and piston as intake valve is closing. I really suggest a .100 clearance here! Adjust to get more clearance by advancing the exhaust cam.

DO NOT RUSH THIS PROCESS! (It is your valves!)


Measure, measure........................................... .......



Regarding Lash clearance.
Do not set stock alfa intake cams less than .016 or exhaust less than .017 unless you want excessive overlap. I specify lash settings for all the RjR/Web cams based on design and application. (commonly .010-.012 Int/ .012/.014 exh.)
Test before closing clearances past this lash setting as performance can be reduced due to excessive overlap, and valve piston interference is more likely than at correct timing events.

I`m always available for consultation, feel free to call! I would appreciate feedback on cams or problems as they should be easily solved. ( unless you didn`t check valve/piston clearance!)

Richard
[email protected]

Richard Jemison
RJR Racing

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post #13 of 22 (permalink) Old 02-23-2014, 03:14 PM
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richard is correct and his method is complete , thorough and accurate but having said that i have found that if you simply snug the assembly together without a head gasket and rotate it slowly by hand you will find out if any issues exist. if it rotates without touching anything without a head gasket then you will be fine when the gasket is installed.
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post #14 of 22 (permalink) Old 02-23-2014, 03:25 PM Thread Starter
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Quote:
Originally Posted by Alfar7 View Post
All you are doing is measuring the combustion chanber distances between pistons and valves at TDC.

If you want to know is what the piston to valve clearances are. You have to build the engine with cams, chains setup at the LCs the builder supplied, and roll the engine through the run cycle.
Richard,

For my clay test, I did set up the engine with cams, chains setup to the LC marks you made and rolled the engine over. Installed the old head gasket as well. Torqued the head to spec.

I like your idea of the ties, but the only ties I had are 0.05 inch. I dont have the thicker ones but I did know where to get the children's clay quicker.

I believe I measured the P2V clearance and all looks ok.

I am just trying to learn why the #4 is different.

Thanks again and I am very excited at trying your new cams and head work.

Sincerely,

Vin

1991 Spider Veloce - Red on Tan - Rosa Bionda
1987 Spider Quadrifoglio - Red on Grey - Rosa - Sold
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post #15 of 22 (permalink) Old 02-24-2014, 02:14 AM
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You haven't got piston number 4 in the wrong way around by any chance?
Pete

'71 1750 Series 2 GTV:
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