Hold That Cam Belt Pulley In Place With This Neat CNC Work

The modern overhead-cam internal combustion engine is a mechanical masterpiece of hundreds of parts in perfect synchronisation. In many cases it depends for that synchronisation upon a flexible toothed belt, and those of you who have replaced one of these belts will know the exacting requirements for keeping the various pulleys in perfect alignment during the process.

[Greolt] had this problem with a dual overhead-cam engine, particularly that the shafts would spring out of alignment on removal of the belt. The solution was one of those beautifully simple hacks that use high-tech methods to make something that is not high-tech in itself but which solves a problem perfectly. He produced a CNC-machined block of HDPE to sit between the two toothed pulleys that was machined exactly to their profiles and which once inserted kept them securely and exactly in alignment.

It’s likely that the same job could easily be done with a 3D printer, and indeed we’ve seen it done with a small piece of soft wood and a hammer. But there is something very elegant indeed about this particular incarnation that we like, it may not be the most complex of the hacks you’ll see here but we’re sure you’ll agree if you’ve ever changed a cambelt, it’s a pretty useful one.

Of course, once you’ve changed that belt, perhaps you’d like to do something with the old one.

Thanks [Brian Moran] for the tip.

73 thoughts on “Hold That Cam Belt Pulley In Place With This Neat CNC Work

    1. It all depends upon the car. On an old Audi 4000, it was a simple job, with the hardest part being the removal/replacement of the AC belt (you had to loosen all 4 mounting bolts of the compressor).

      1. I did belts on my Subaru a few months back.

        That’s four(!) camshafts, a crankshaft and a few other pulleys.

        And no, i am not a car mechanic but an IT guy. I did it partially for shits and giggles (i do love working on my car), necessity (i was at 120k km and starting to worry) and pure spite. The mechanic i would’ve gone to to get it done was busy with a restoration and had no time. He did not expect me to say “alright, when?” when he half-jokingly said “You can do it here by yourself if you want to.”

        I learned a lot during those 12 hours. One of many things was that i’m never going to do belts myself again.

        1. “One of many things was that i’m never going to do belts myself again.”
          Although it was “only” one camshaft, it took about 2 days to swap the timing belt in my (1.4 L SOHC) Suzuki Sidekick.
          But as the newt guy in “Search of the Holy Grail” said, “I got better.”; getting it down to 4 hours.
          So, I say don’t give up! But I won’t hold it against you if you don’t.

          1. Oh, i’ve opted to do other things people usually don’t do.

            A month ago i wanted to do my rear wheel bearings. One was properly shagged, but i don’t like doing one side only.
            After 8 hours i was done…with one of two. 8 friggin hours, including the use of an acetylene torch (Can’t be tight if it’s a liquid, inner bearing race didn’t want to come off the hub).
            Went to another guy i know to get the second done, because my other shop had closed for winter vacation.
            This legend did it in 1.5h.

        2. IT and car mechanic intersect deeply. You apply the same logic to both fields really. Most car guys that say they don’t know about computers just didn’t get the chance to realize they could use the same procedural problem solving they do on a daily basis.

    2. I like my old pushrod engines too. I got a CX650 with some of the strangest engine geometry you’ll ever see. Both heads of the v-twin are twisted about 20°, the camshaft is nestled between them, and the angles of the rods and rockers make some interesting organic-looking shapes such that I have a hard time imagining how they were properly designed. It’s a cool little motor.


      1. That exhaust looks expensive, and like an absolutely horrible hack job. Has the manufacturer not heard of things like full diameter mandrel bending? How about hydraulic forming? Could CNC mill steel molds, pop the pipes in and force them out to be full diameter.

        That exhaust has 16 welds in each tube. Unless the weldor painstakingly ground and smoothed each weld before welding on the next piece, it would be rough inside, causing all kinds of turbulence and restriction.

          1. And they were all heavy, slow and hideous.
            (I should know, I had one as my only transport for years)
            Also, to bring this almost back to topic, they had a notoriously weak cam-chain tensioning system, and as the cam-chain was at the back, swapping it was an engine-out task. As was anything which needed doing to the alternator, also a weak spot, and at the back of the engine.
            Yes, this miracle of Japanese technology managed to have both pushrods _and_ a camchain.

        1. Agreed on the exhaust. Unless mounting or other external factors necessitated it, there’s too many bends, too many welds (what was the purpose of the last welds after the crossover?) and unnecessarily tight radius turns in the pipes. Props for taking on a project like that, but it looks like a classic case of form before function.

  1. Neat solution but, while not needing to do this myself, I always thought the ‘free’ solution was splitting the belt? (your split it down the length, replace the outside half with the new belt, cut the remainder of the old one and then push the new belt home). Are belts too tough (or not tough enough) to do that?

      1. nope, thats a legit method of maintaining cam timing, I dont do it myself, I prefer locking tools and/or tip-ex pen markings (along with any OE markings, technique depends on the engine and its idiosyncrasies ) but i wouldn’t give anyone grief for using this method. (mechanic for about 15 years and now owner of my own place, have put 4 apprentices threw college)

        I have never used locking blocks like cited in this article, but if your a home gamer they will make your life much easier on some engines where the markings dont quite line up level.

        the only downside of relying on the cut belt method is if your repairing an engine after a belt failure and thats the only method you know.. your in for a big leap of faith timing up from scratch :)

      2. I have used this method 100+ times as a factory tech on both Ford and Honda. If the original belt was intact, this is what you do. If it was broken, you pull the head (not always, but far too many engines have valves that interfere with the pistons)

      1. Yeah, but the cost to replace is fairly high due to the labor required and hence many owners don’t change the belt leading to engine destruction for someone.

        My nephew has an Aveo which requires a belt every 60k and at 120k had no indication it had been replaced before. That was about a four hour job for me (home mechanic) and $200 in parts/fluids. At least my labor for family is free.

        If I didn’t absolutely ride the ass of his mother about the belt, I’m sure they’d still be risking it to this day.

        1. Yes never doubt the average car owner’s distaste for preventative maintenance!

          Modern timing chain engines aren’t without their flaws though. Plenty of them use plastic guides or tensioners that are prone to fail. All in all, discounting deeply flawed or complex designs, I think it’s silly to compromise your choice of vehicle because of the timing system.

          1. This is very true! Although generally a vehicle with a timing chain can kind of tough it out until the owner’s neglect catches up to the rest of the vehicle. ;)

            Come to think of it, I’m pretty sure I covered the cost of the timing belt for my Nephew as a Christmas gift.

          2. Timing chain engines are far too often cost cutted so they have same service interval as a good cambelt engine.

            What does confuse me is the fact pushrods isn’t used for diesel engines in “ordinary” cars, given their low-rev nature compared to gasoline.
            Most of them are built for long service intervals and high mileage anyway, so going that one extra step only makes sense.

          3. 2004 Dodge Dakota with OHC V8. Three timing chains, four sprockets, two hydraulic tensioners. The plastic guides were intact but broke apart in my hands when I removed them.

            Crazy thing about that engine is that at over 140,000 miles the original crosshatch honing marks were visible in the cylinders. WTH iron alloy did Chrysler use on those blocks? Had to replace the heads because unlike the apparently indestructible block, the heads like to have the steel exhaust valve seats fall out of the aluminum.

            With a rebuilt pair of heads and all new timing stuff it was like a new engine.

        1. Same with the V8 Audi S4. I briefly considered owning one until I found out what replacing the timing guides and tensioners was all about. It is truly a beautiful and terrifying design.

      2. I’ll stick with my 5.3L LS based engine with timing chains that’s got 196k on it (and climbing daily) that’s had ZERO maintenance other than oil, filters and a set of spark plugs (getting ready for set #2).

    1. there are several solutions from gear driven to pneumatic (google freevalve) and the most efficient solution is to ditch the internal combustion engine and go completely electric. The mis understanding is that often engineers have to make trade offs that consider cost, NVH and maintenance as well as capability and efficiency. trying to take a shot at engineers because they have continued to timing belts is disingenuous and tantamount to taking a shot at engineers for continuing to design internal combustion engines. Rather than trying to think that you can try to teach engineers to do it better, how about fully understanding why they made the decisions they have made.

    2. interestingly I see more timing chain failures before 100k miles than timing belt failures, and over 100k waaaaaaay more chain failures as people know they should be changing belts! .. interestingly, a few manufacturers have dabbled “wet” as in, soaked in engine oil, timing belts.. they are fun to work with.. this may be a UK/europe thing though as the US doeesnt seem to have much love for complicated little engines, especially diesels.

      1. EDIT — the whole reason I had that wee rant, is belts are atleast designed to be serviced. chains are usually well buried and make a belt look like a regular service. with BMW and Mercedes moving to timing chains at the flywheel end, and making those chains out of butter, things are only getting better :(

        1. ” chains are usually well buried and make a belt look like a regular service. ”

          I disagree, having to remove coolant bottle, engine mount, power steering reservoir, timing covers, cut off aux belts, time up engine, and remove idler pully to even get to the point you can remove the timing belt… Took approx 9 hours outside my front door. Good learning experience though!

          1. now remove cam cover, exhaust, sump, water pump, timing cover to do the chain on your average transverse 4 cylinder (most common engine layout here in the UK) and removing a handful of reservoirs for access, which are usually supplied with hoses long enough to be unbolted and swung out the way, and a belt is much much easier.

            obviously this is all subjective. to do the rear timing belt on a TDV6 rangerover your supposed to lift the body off the chassis, and to do the timing chain on a bmw N45 you need about 3-4 hours tops with the correct tools. an experienced tech could probably get that to under 2 hours.

    3. Don’t blame the engineers, please. They might have known better. They might have wanted to do better.

      But some donkey said “That’s too complex/expensive/noisy, do it differently.”

  2. i plan on using zip ties and a white marker to mark the placement in case something moves. Wait, aren’t there marking on timing gears themselves in case they are out of alignment?

    1. There are marks and you can even see them in the photo. The problem is that camshafts will want to “snap” to certain positions throughout their rotation because the loads placed on the cam are not consistent throughout their rotation. IE, there may be four positions the cam wants to rest in, but none of those may line up with where the cam needs to be aligned for belt replacement.

      The irony is that I recognize that engine as it looks identical to the Aveo I worked on last year. While the cams did want to snap to a position that wasn’t aligned, I was able to get them close enough to get the belt in place and “pull” the cams into alignment as the belt was tightened. That said it took several tries and I would have readily accepted such a tool.

    2. push the belt off the back of the pulleys and slide the new on the front. Once you have the new belt on the pulleys enough to prevent movement, cut the old one and finish sliding the new one on.

  3. On my zetec is not only the pulleys to hold in place. You have to hold usually first cylinder in dead top. And on zetec you use a flat metal bar on the other end of the camshafts to hold it.

      1. Don’t forget that overloaded engine mount, that’s in the middle of it all.
        Nothing like that dash rattle, at idle, to let you know it’s collapsing again.
        I truly miss having one as a daily/city driver, But I’m thoroughly done with front wheel drive vehicles and their mechanical cluster f***s.

        1. AFAIK they have had them through the entire ej** production V3 onwards(im sure a subaru person will correct me, and dont ask what year, im not enough of an anorack to know :( lol), if your in a situation where the pulleys shatter, youd chew up a belt on the steel pulleys anyway, of more concern should be the hydraulic tensioner and idlers, a full kit is expensive, so often people swap the belt alone, usually the tensioners leaking and 1 or 2 idlers are rough and should be changed. so if the cars had a belt done it would be worth checking.

          1. That is just too bizarre. I don’t understand why’d you want to have the pulleys shatter to save a belt. Doesn’t that just destroy the entire engine anyway? Am I missing something here? Is it a non-interference engine?

          2. I think the idea is the pulleys shatter and the engine stops dead. yes they are interference. risk the engine to save a life. either that or they made the pulleys that way for cost reasons and im just spreading hear-say.

  4. My question is simple. We’ve been building engines for 100+ years. Why, after all this time are the timing marks still so BAD?

    It’s always “locate these three little dots (now which of these two teeth do they actually match?) and line them up with this vague triangular mark on the block two inches away” Repeat three times. While performing gymnastics and covered with grease.

    Of all the simple, simple things that could make working on a car easier, why can’t there be CLEAR alignment marks?

    1. Agreed. I was aligning an AMC engine and it was supposed to be aligned using a triagle on the gear. I was wondering quite a while why it seemed just a little bit off. Thankfully i didn’t give up on the nagging in my head, because then i noticed a smaller triangle on it. I used that and it aligned correctly. Damn i hate this sort of crap.

      1. Yeah, my Suzuki Sidekick had a couple of “timing marks” on one of the belt pulleys, about 70 degrees apart.
        Good thing it was mentioned which one to use in the online instructions I found.

    2. I had a Chevrolet Chevette, and it went better than timing marks. It had holes in the flywheel and the cam pulley. One fit a 1/4″ drillbit, and the other fit a 5/16″ drillbit. So you jammed a drillbit through the hole, rotated the pulley until the drillbit stuck into the matching hole in the block/head, and your alignment was assured. It was a lovely idea, and that’s the only engine on which I’ve ever seen it implemented.

    3. My 25 year old citroen bx 1.6 has holes in both the weels and the block. You just stick in two 8mm pins and change the belt. It takes two hours as there is a lousy screw on the timing belt cover…
      But maybe that is patented. :)

    4. I dunno much ’bout your make and model, those might could be for using a timing strobelight
      so as to adjust the distributor for optimal spark. Generally, the spark needs to light off at a few degrees before TDC. I use a rod to determine true TDC

  5. I recently had the timing belt changed and an oil pump that fit the teeth on the belt. I kept both because they looked perfect for MAKING a cnc machine. Lol

  6. To all ya running a 91 Honda Civic, if you don’t know when your timing belt was replaced… replace it. July 30, last year, hottest day, driving up a big hill [Chickies], the water pump seized, runs off timing belt,shredding it. The SOHC stopped at the place where all the valves are almost closed, sending a camera down into the cylinders revealed no visible valve/piston collisions, ordered a kit of belt,pump,and tensioner. Getting the crankshaft pulley off took 2 helpers, a crowbar to hold the pulley fast, a 3/8 breaker bar using leg muscle, and me hitting the bolt w/ a hammer. Ya that bolt is standard threads, and the engine turns CCW go figure. Retiming it wasn’t all that hard, OHC has marks, the pulley them too. She’s still running great!!

    1. D series is a non interference engine when not in vtec – which didn’t come till 95.
      Same for B series out of vtec.

      Honda handily put alignment holes in the top of the camshaft retainer bars which lock the cams in place on a DOHC engine. Unsure on SOHC, been a while.

    2. I’m still upset with Honda.
      Back in the 1980’s, when they found out their timing belts were breaking and causing expensive engine damage.
      They sent out a bulletin to the owners saying there was a misprint in the Owner’s Manual; Change the Timing Belt every 60,000 miles.

      1. I hear ya, running an H20 pump off the timing belt is a “bad idea”. They did it. So to append my post, get the complete kit, change out everything in there. Only took me 2 weeks, during the hottest time of year. Crankshaft pulley had holes, ran an antenna U bolt/strap to hold the crowbar. I didn’t get a speeding ticket, Civic gave me one

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