I am currently building up a Fiat/Lancia 1800 and am not 100% on where the crankshaft needs to be to mark out the valve reliefs on the pistons using a sharpened old valve? It seems that at TDC the reliefs might be a bit far in towards the center of the piston when compared to the OEM Fiat reliefs which sit close to the outer edge of the piston (say 2mm in).
I have also had no luck in finding out how much offset is used on number #1 and #4 pistons for the reliefs. I will be able to work this out, but it just seems like it is an illusive bit of information.
Help: Correct way to mark valve reliefs?
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maytag
- Posts: 1789
- Joined: Mon Oct 19, 2009 9:22 pm
- Your car is a: 1976 124 spider
- Location: Rocky Mountains....UTAH! (Not Colorado)
Re: Help: Correct way to mark valve reliefs?
the closer to TDC you are, the further AWAY from the center of the piston your mark will be. Put it at TDC.
I don't know what the offset amount is either, but if you are marking them, you really don't need to know the measurement, do you?
I don't know what the offset amount is either, but if you are marking them, you really don't need to know the measurement, do you?
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!
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vortspeloce
Re: Help: Correct way to mark valve reliefs?
I am intending to mark my existing pistons and then send them in to one of the forged piston vendors. I thought they were closet to the edge at TDC, but read that this is not the way to do it. So I am not 100% on it.maytag wrote:the closer to TDC you are, the further AWAY from the center of the piston your mark will be. Put it at TDC.
I don't know what the offset amount is either, but if you are marking them, you really don't need to know the measurement, do you?
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vandor
- Posts: 3996
- Joined: Sat May 23, 2009 1:23 pm
- Your car is a: 1971 124 Spider
- Location: Texas, USA
Re: Help: Correct way to mark valve reliefs?
You can measure the distance between the tops of the valve guides if the valves are out.
Csaba
'71 124 Spider, much modified
'17 124 Abarth, silver
http://italiancarclub.com/csaba/
Co-owner of the best dang Fiat parts place in town
'71 124 Spider, much modified
'17 124 Abarth, silver
http://italiancarclub.com/csaba/
Co-owner of the best dang Fiat parts place in town
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maytag
- Posts: 1789
- Joined: Mon Oct 19, 2009 9:22 pm
- Your car is a: 1976 124 spider
- Location: Rocky Mountains....UTAH! (Not Colorado)
Re: Help: Correct way to mark valve reliefs?
your piston manufacturer will also need to know the angle of the valve, in relation to the vertical piston.
and I may be misreading your posts, but it seems you've said two different things there. in the first post, you comment that you think the valves will be too close towards the center at TDC. but in the last post you say that you think they are closest to the edge at TDC.
Maybe I'm misreading you.
but your latter supposition is the correct one: at TDC, your valves would strike the pistons closer to the edge of the piston than at any other piston position.
and I may be misreading your posts, but it seems you've said two different things there. in the first post, you comment that you think the valves will be too close towards the center at TDC. but in the last post you say that you think they are closest to the edge at TDC.
Maybe I'm misreading you.
but your latter supposition is the correct one: at TDC, your valves would strike the pistons closer to the edge of the piston than at any other piston position.
I'm no Boy-Racer..... but if I can't take every on-ramp at TWICE the posted limit.... I'm a total failure!
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vortspeloce
Re: Help: Correct way to mark valve reliefs?
Thanks for the tip Csaba. I had not thought about measuring between the valve guides. I will think some more about this and what it may yield.
Maytag: I have the valve angles at hand, it is just the offset(s) that are the concern. When I say offsets, I should really clarify. There are two offsets that are of concern for the valve reliefs. The first is the offset from the outer circumference of the piston which "should" be the same point across all pistons. This is the one I am most concerned about at the moment. The second offset is the offset that #1 and #4 pistons have towards #2 and #3, say the center cylinders. It is my understanding that for some reason (crankcase casting reuse between models/years?) the combustion chambers in the head are not directly above each cylinder bore in the block. There is a slight offset of something like 3mm on combustion chambers #1 and #4 towards the middle of the head.
As far as my post, what I mean to say is that the valve reliefs marked with my sharpened valve are towards the center of the piston, whereas the OEM valve reliefs in the cast piston I am marking are very much towards the outer circumference. Every set of valve reliefs that I have seen tend to be towards the outer circumference of the piston, whereas the ones that I have marked with the sharpened valve are towards the center of the piston. This makes me think I am doing something wrong.
The key question is: Should I punch the pistons with my sharpened valve when the piston is at TDC or should I be doing it at some other timing point? I know that with some heads the marking is meant to be made at the full lift point where the valves are closest to the piston, not TDC.
I will post some photos of the points I have punched for further clarification.
Maytag: I have the valve angles at hand, it is just the offset(s) that are the concern. When I say offsets, I should really clarify. There are two offsets that are of concern for the valve reliefs. The first is the offset from the outer circumference of the piston which "should" be the same point across all pistons. This is the one I am most concerned about at the moment. The second offset is the offset that #1 and #4 pistons have towards #2 and #3, say the center cylinders. It is my understanding that for some reason (crankcase casting reuse between models/years?) the combustion chambers in the head are not directly above each cylinder bore in the block. There is a slight offset of something like 3mm on combustion chambers #1 and #4 towards the middle of the head.
As far as my post, what I mean to say is that the valve reliefs marked with my sharpened valve are towards the center of the piston, whereas the OEM valve reliefs in the cast piston I am marking are very much towards the outer circumference. Every set of valve reliefs that I have seen tend to be towards the outer circumference of the piston, whereas the ones that I have marked with the sharpened valve are towards the center of the piston. This makes me think I am doing something wrong.
The key question is: Should I punch the pistons with my sharpened valve when the piston is at TDC or should I be doing it at some other timing point? I know that with some heads the marking is meant to be made at the full lift point where the valves are closest to the piston, not TDC.
I will post some photos of the points I have punched for further clarification.
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BEEK
- Posts: 1833
- Joined: Wed Mar 24, 2010 10:45 pm
- Your car is a: 1975 Spider
- Location: clermont fl
Re: Help: Correct way to mark valve reliefs?
guy croft makes the pistons you are looking for
Automotive Service Technology Instructor (34 year Fiat mechanic)
75 spider , 6 Lancia Scorpions, 2018 Abarth Spider, 500X wifes, 500L 3 82 Zagatos. 82 spider 34k original miles, 83 pininfarina, 8 fiat spider parts cars
son has 78 spider
75 spider , 6 Lancia Scorpions, 2018 Abarth Spider, 500X wifes, 500L 3 82 Zagatos. 82 spider 34k original miles, 83 pininfarina, 8 fiat spider parts cars
son has 78 spider
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timinator
Re: Help: Correct way to mark valve reliefs?
Checking valve clearance with clay is an easy way to go. Checking springs will help too. Check exhaust at 10 btdc and intake at 10 atdc. You might find the cutouts are big enough already. Using a vertical clearance of 0.100 in. and radial of 0.050 in. is typical. If the cams are going to be run advanced you need to make another check after the cutouts are roughed in.