Timing Belts - Cam Locks

Not surprised, often the cams on a 2V engine tend to stay in place.

This is NOT the case for the 4V. The 4V front bank cams are much less stable (greater spring pressure from the dual valves). In particular the front bank intake cam won't stay in place.

BTW, just double checked my memory, my hp business cards are 0.009" thick.

 

I did not read the threads but totally respect Dave Helms. I did not invent the matchbook but I use it all the time. And though my name is fatbillybob this method was not invented by people who married their cousins and lost some brain cells. You could conceiveably destroy a cam cap and I guess people have done it. The cam caps survive 8000rpm and probably more force beyond that as a design feature. I don't understand your math but don't dispute it either. Me hand tightening paper in there for the sake of cam bolt removal/install is nothing. I can't imagine that I can make 1200lb of force by hand on 8mm nuts. That much should surely destroy something. Any method can be abused. I have seen people ruin simple oil changes. If you think the paper use is scary you should watch the forces a dentist puts on your tooth when he trys to pull it out. I understand your concern and respect your opinion but believe that it is a non-issue and directly relates to how belts are properly timed and tensioned. In my opinion car repair is part of a complete treatment plan. Without a complete plan we make unknown compromises. In my treatment plan...cams out lead to easy valve adjustment, leads to locking cams, leads to proper equalized belt tension by unpinning cam cogs... So as to not open that up again I'll go back to agreeing to disagree. I cannot talk about one issue without talking about the other as they are part of treating the whole patient not just the symptoms of the patient which is one reason why we could all agree that medicine in america is pretty screwed up.

 

We may not be that far apart on the specifics of the paper/cam cap itechnique .

Just went back & read your original post. Picked up on a couple of things that hadn't registered before:

I also use an air wrench to break the bolts loose for the same reason. The inertia of the cam resists most of the force pulses. In the impact wrench case, the paper doesn't have to provide anywhere near the forces I calculated for the hand wrenching case in my previous post.

BTW,Are you also saying you have a method of torqueing the bolts with an air wrench? I can set my butterfly wrench up to come close, usually a 1/2 turn with the torque wrench puts them spot on.

Razor blade covers are also significantly thinner than match book covers. Just measured one, it was 0.0098, ~= business card thickness. A couple of matchbook covers measured almost 2x that: 0.018 & 0.022 respectively.

Again, that's essentially finger tight.

It's also a 'feel' thing. You & I & all the other long-time wrench turners have that feel. We've broken & stripped our share of bolts, & used torque wrenches a lot. However, a lot of the newbies, & even people who have done a fair amount of self-maintenance yet to develop that feel.

I think the paper/cam cap technique was developed by very experienced & skilled mechanics who had the skill & judgement to use it safely. It's the 'skill' & 'judgement' element necessary to safely use the paper under the cam caps technique that keeps me from recommending it to someone who's skill level is unknown, or is an obvious novice.

 

Hmmmmm- was that meant for me??

As Verell knows, I tend to gorilla things when I have a wrench in my hand.

Sorry for the hijack- this is a very useful post for everyone and I've learned quite a bit from it. Thanks

 

Umm,
Wasn't going to mention that I recently worked with a reasonably experienced fchat member, who broke an 8mm stud with a 1/4" ratchet while 'tightening it a bit'. Could just imagine what he'd do tightening a cam cap 'finger tight'...

 

Agreed. We often take for granted our personal skills developed over many years. I would hope and assume a novice would work his way up to this level. I do not think someone who really dosen't understand how or why we check oil on a dry sump motor should be trying to figure out how to depress valve buckets and remove tappets. Learning is a gradual process like anything else. I think it is great to work with a mentor such as yourself to move to the next level or at least to have the confidence that if I was a novice and got stuck you would know what to do. In my case I bootleg hired FNA mechanics for a specific project so I could watch and learn. In a nutshell in medical school it is read about the surgery, watch the surgery, do the surgery with and experienced surgeon, then do it by yourself. If you start really thinking about your surgical problems you end up pioneering the mechanical heart. I have taken mostly this same approach and sometimes I get brave and chop up a clutch or suspension for my own compromises.

 

Yeah that's the way to do it. And if you get stuck or don't know... step back think about it and post here on Fchat. We will get you running again. Always "measure twice and cut once". Good luck you will be highly satisfied when you accomplish your goal.

 

Could someone post some pictures of the matchbook cam lock, I think I understand. It simply introduces friction between the cam shaft and the bearing. With my 75 GT4, how critical is this step?

Also the head will be completely torn down for repair and parts replacement. Do I just mark well where the engine is now and only do one side at a time, or I remove both heads at once and just reset the timing to TDC when the engine comes back together?

Thanks for any help.

Mike

 

If you have to ask, don't try this method, & certainly don't use a match book cover, it's too thick (see earlier posts in this thread).

The 2V engines cams tend to stay in place, you can do the job w/o cam locks. However, they do make it easier.

I'd recommend some other cam locking method. Either use a pair of vice grips with lots of tape on the jaws on the cams, or get a set of my wooden cam locks, they do the job & there's no risk to the cam caps.

Before disassembly, note how each cam gear is pinned to it's cam (ie: which cam gear & cam flange holes are pinned together).

After reassembly, put the engine on PM1-4 & re-pin each cam, then install a belt & see how close your cams are to the marks.

TIP:
I use 15/32" drill bits with lots of masking tape over the cutting ends as trial pins. They're lots easier to get in & out while fine-adjusting the cam gear timing. Once I've got the pin positions sorted out, I just pull them out & insert the real pins.

Hmm,
Ought to make some trial pins out of brass rod with knurled ends...

 

I'm a little late to this discussion. I have only done three Ferrari belt changes in my life (actually I mostly watched the first one, helped with the second one, and did the last one myself). Since Verell taught me, I use Verell's method, and I have to say, it seems to work very well. That being said, Fatbillybob's method seems like it *could* be slightly more accurate (i.e. to lock the cams, let the cam pulleys be loose, tension the belts, then re-pin the pulleys). But I really think Martin (marankie) makes a very valid point, that we are splitting hairs here on a set of cams that probably doesn't need it. For a race car that needs to be 101% at all times, sure, but on my street 308, I doubt it makes a difference if they are a fraction of a degree from perfect.

The main advantage of Verell's method is that it can be used when you just want to change the belts without pulling the cam covers. Sure, this means you must rely on a previous "correct" timing, but for a lot of people the belt change is not part of a service because not enough miles have been driven to warrant a valve clearance check. If the seals aren't leaking, and the valves don't need adjusting, why create more of a job than necessary when you just want to be sure you have fresh belts on the car? The fact is that a lot of owners are frightened by doing a belt change when it's pretty easy. If they are too cheap to take it to be serviced, they drive around with old belts that could go at any time. I would rather see DIY shadetree mechanics like myself do a "98% perfect" belt change and have new belts, than drive around in a time bomb! Verell's method is easy enough that it won't frighten off a newbie and accurate enough that I'll bet nobody can tell the difference. Fatbillybob's method appeals to the more advanced mechanic who is going for 101% perfection, of which there are many on this board (with me not being one of them!)

This discussion has been very educational to me and I learned something, so thanks!

Birdman

 

Thanks for thinking of me as advanced but really I think you are wrong. Many DIY'ers get into trouble because they really do not understand what or why they are doing something. Someone just told them to do it this way. They are part replacers. Many paid mechanics are part replacers too and there in lay the problems. Many relie on computers chips to diagnose their problems never really understanding how things work. My system is only advanced because it strives that you understand the basics...those critical elements that are at the basic route of function. It is the egg and sperm. I've been in mixed martial arts for over 30 years at a very high level and instructor level. I tell you the most important thing I have learned over 30+ years of learning the coolest stuff on the planet is that at the end of the day it is the "basics" that weill never fail you from any angle you want to look at a problem. Truely understanding the basics is a very advanced technique. Many just want more tools for the tool box. The goal however is to have the smallest box that can do the most things. So grasshoppers go out and give it a whirl it is only a car...there is always someone like me of Verrell to point you in the right direction. And you can believe that Verrell and I are still learning from anyone and everyone.

 

You're right, you're not!