First let me say my engine does have adjustable cam pulleys, you just can't see them. They are done with pins on the inner diameter. I have always had an issue with the ajustable ones that are only held in place with the friction of 6mm screws. Has anyone ever had problems with the cam timing changing due to bolt slippage? I am trying to design a pulley that has a positive adjustment that would prevent any slippage. Is it needed?
Hal
Cam Pulleys
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manoa matt
- Posts: 3442
- Joined: Thu Oct 26, 2006 4:28 pm
- Your car is a: 1978 Fiat 124 Spider 1800
- Location: Honolulu, Hawaii
Re: Cam Pulleys
When I got my adjustable pullies with the 6mm allen head bolts, I asked about the torque spec for the adjustment bolts. Here was my question and the reply:
"What torque spec do you recommend for the allen head bolts on the cam pulleys? Any type of securement of the bolts, split ring lock washer, internal or external "crown" style lock washer, thread locker?
"The screws should be torqued to 6 lb-ft. I don't know of any situations where the screws back off, but for extra insurance you can use loctite if you'd like. I do not recommend split lock washers on soft materials like the stainless bolts or on aluminum."
Hal, I'm pretty sure if you were to use a split ring lock washer it will cut into the aluminum, howerver if you were to use a crown style either internal or external lock washer, the bolt head will press the lock washer ever so slightly into the aluminum and bite it enough to prevent it from slipping. Alternatively once you get them set up you could drill through both the aluminum and cast iron sections and insert a roll pin. A more elelgant solution might be to cut grooves or flutes into the aluminum face and install a washer under the bolt head with a small ridge on it to catch the flutes.
The ultimate would be if the two mating surfaces had micro flutes similar to how the windshield wiper arms mount on the wiper rack posts, however that might eliminate some of the fine tuning adjustability of the pullys.
"What torque spec do you recommend for the allen head bolts on the cam pulleys? Any type of securement of the bolts, split ring lock washer, internal or external "crown" style lock washer, thread locker?
"The screws should be torqued to 6 lb-ft. I don't know of any situations where the screws back off, but for extra insurance you can use loctite if you'd like. I do not recommend split lock washers on soft materials like the stainless bolts or on aluminum."
Hal, I'm pretty sure if you were to use a split ring lock washer it will cut into the aluminum, howerver if you were to use a crown style either internal or external lock washer, the bolt head will press the lock washer ever so slightly into the aluminum and bite it enough to prevent it from slipping. Alternatively once you get them set up you could drill through both the aluminum and cast iron sections and insert a roll pin. A more elelgant solution might be to cut grooves or flutes into the aluminum face and install a washer under the bolt head with a small ridge on it to catch the flutes.
The ultimate would be if the two mating surfaces had micro flutes similar to how the windshield wiper arms mount on the wiper rack posts, however that might eliminate some of the fine tuning adjustability of the pullys.
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ventura ace
Re: Cam Pulleys
Hal,
I have adjustable cam pulleys from Jason Miller -- maybe yours are the same. They have six 6 mm socket head cap screws that attach the aluminum center hub of the pulley to the steel outer ring. The screw threads are in the steel, and the bolt grip of the head of the screw is on the aluminum. I used a steel flat washer against the aluminum, with a split lock washer between the flat washer and the head of the screw. I've never used a torque wrench to tighten them, but merely pulled pretty hard on my 5 mm allen wrench. I checked the torque tonight, and it's betwen 9 - 10 ft-lbs. I haven't had any problems with them moving on me (25K miles with them).
Alvon
I have adjustable cam pulleys from Jason Miller -- maybe yours are the same. They have six 6 mm socket head cap screws that attach the aluminum center hub of the pulley to the steel outer ring. The screw threads are in the steel, and the bolt grip of the head of the screw is on the aluminum. I used a steel flat washer against the aluminum, with a split lock washer between the flat washer and the head of the screw. I've never used a torque wrench to tighten them, but merely pulled pretty hard on my 5 mm allen wrench. I checked the torque tonight, and it's betwen 9 - 10 ft-lbs. I haven't had any problems with them moving on me (25K miles with them).
Alvon
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kmac33
- Posts: 509
- Joined: Thu May 22, 2008 11:19 am
- Your car is a: 1974 Spider
- Location: Lilburn/Stone Mountain Georgia
Re: Cam Pulleys
I have Jason Miller's pulleys as well. Torqued to 8 lbs with Loctite. They have not budged.
Kevin McMullen
1974 Fiat Spider - Restoration Complete! But the mods/refinements continue
1980 Fiat Spider
2013 Subaru WRX
1974 Fiat Spider - Restoration Complete! But the mods/refinements continue
1980 Fiat Spider
2013 Subaru WRX
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pastaroni34
Re: Cam Pulleys
Slipping was a concern of mine when I first started playing with these things. I came up with a couple of more exotic designs, one with an eccentric bolt for adjustment, another that had a vernier screw adjustment. They are for the most part horribly complicated. I decided a simple slotted joint was good enough and did a few calculations.
Even though my design utilized M6 bolts, the clamping load is reasonably high. Multiply that by 6 screws, and you've really got a lot of force (10000lbs) pushing the center piece to the outer cog/gear. After applying a friction coefficient etc.. the joint has roughly 1000lb-ft torque capacity. It takes less than 30lb-ft to turn the camshaft. Even if half the screws fail there's plenty of room for safety.
The way I see it, the most significant factor is overloading (over torquing) the M6 bolts. After doing some more research (since 6 years ago) into joints and fasteners, I have new recommendations for how best to fasten the pulleys:
1 - Use copper based antisieze compound between the bolt heads and washers. This keeps the bolts from galling against the washers and provides more consistent torque readings. Other anti-galling compounds may be used but copper is the cheapest and most readily available. I do not recommend motor oil.
2 - Use Loctite 243 on bolt threads. This provides resistance to backing out the screw due to vibration etc..
- OR Use Loctite 271 on threads for permanent holding (after you no longer want to change the timing). You must use heat to break the bond and remove the screws.
3 - In all situations threads must be cleaned (no residual Loctite etc) and torqued to 6ft-lbs (72lb-in). Furthermore, bolts should be tightened in a crisscross pattern.
The bolts I supply are A2 stainless (aka 304 or 18-8, its kinda a mixed bag these days), which are relatively weak in the world of bolts. These were chosen for corrosion resistance, low price, and because there was no need for a stronger fastener.
Even though my design utilized M6 bolts, the clamping load is reasonably high. Multiply that by 6 screws, and you've really got a lot of force (10000lbs) pushing the center piece to the outer cog/gear. After applying a friction coefficient etc.. the joint has roughly 1000lb-ft torque capacity. It takes less than 30lb-ft to turn the camshaft. Even if half the screws fail there's plenty of room for safety.
The way I see it, the most significant factor is overloading (over torquing) the M6 bolts. After doing some more research (since 6 years ago) into joints and fasteners, I have new recommendations for how best to fasten the pulleys:
1 - Use copper based antisieze compound between the bolt heads and washers. This keeps the bolts from galling against the washers and provides more consistent torque readings. Other anti-galling compounds may be used but copper is the cheapest and most readily available. I do not recommend motor oil.
2 - Use Loctite 243 on bolt threads. This provides resistance to backing out the screw due to vibration etc..
- OR Use Loctite 271 on threads for permanent holding (after you no longer want to change the timing). You must use heat to break the bond and remove the screws.
3 - In all situations threads must be cleaned (no residual Loctite etc) and torqued to 6ft-lbs (72lb-in). Furthermore, bolts should be tightened in a crisscross pattern.
The bolts I supply are A2 stainless (aka 304 or 18-8, its kinda a mixed bag these days), which are relatively weak in the world of bolts. These were chosen for corrosion resistance, low price, and because there was no need for a stronger fastener.
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halg
Re: Cam Pulleys
Sometimes I do things just because I can. I am a machinist by trade. It has been suggested that I may be able to help my low boost by reducing the overlap timed into my cams. While I can do it with the system I have, it isn't quick and easy. Hence the reason to look at a different way. Jason , it is great to see someone that has a working product, trying to either improve or at least verify that everything has been done to make it the best it can be. While I will probably never buy one of your products(I make my own) keep up the good work.
Hal
Hal
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halg
Re: Cam Pulleys
I would like to thank all who responded. It seems that everyone has concerns about slippage even though no one has ever experienced any. Like I said sometimes I do things just because I can. Here are my new adjustable cam pulleys with positive stops. They are still fully adjustable.
Hal
http://flic.kr/p/8x5Nrr
Hal
http://flic.kr/p/8x5Nrr