how to build an engine at the speed of plate tectonics

It's been about three or four weeks, now, that I've planned to make big progress on the engine build over the weekend, and then gotten about half a step into the job and not been able to go any further.

After getting the lower end together, the next thing was to install the cam and timing gears.  So, I sat down one Saturday morning and pulled out the instructions for installing the timing gears.  The instructions said to install the cam thrust plate.  Cam thrust plate ... cam thrust plate ... I don't have a cam thrust plate.

Turns out that big block Chevys before the 1980s didn't have cam thrust plates.  During that era, they all had flat tappet cams, and since the cam lobes are ground on an angle in order to spin the tappets, they decided to use that angle to also make the tappets constantly push the cam back in the block.  That way, you only need one thrust surface, which is where the back of the cam timing gear rides on the front of the engine block.

But, if you use a roller cam, then your lifters aren't supposed to spin, so there's no angle on the cam lobe, which means that it is free to move forwards in the block, which means you need to stop it from doing that.  This is done by way of a "cam button," which is installed on the front of the cam, and which butts up against the inside of the timing cover to keep the cam from moving forwards.

The two main types of cam button are nylon, or roller.  The nylon button is a hunk of nylon that rubs on the timing cover.  The roller button is steel and has roller bearings so that it doesn't rub on the inside of the timing cover.  It costs about twice as much as the nylon button, but that's about $8 compared to about $4, so I decided to get the roller button.

It seemed to me at the time that the stock stamped steel timing cover would be a little flimsy for locating the cam, but they say this is how it's done, so I just went ahead and ordered a cam button.

In the mean time, I decided to at least install the crank timing gear.  Comp Cams recommends that you buy a tool and an adapter for this job, but it's kind of expensive, and I thought, hey, I can make that stuff, and save some money.  So, I made an adapter out of a piece of pipe, and I figured I'd just use a harmonic balancer bolt to pull the balancer on (that's what I did on the Corvair).

To make the adapter, I used a pipe nipple and a pipe cap.  The pipe was large enough to fit over the crank snout, but it was also big enough for the harmonic balancer bolt to fit through.  By cutting the end off of the cap and flipping it around, I could make a piece that would prevent the bolt from passing through the pipe.

Here are pictures of the pipe pieces, to show the concept:

 

As purchased:

As modified:

As assembled:

So, I had an adapter, but it was a little too long for the bolt to reach through it, so I cut it down a bit.  Trouble was, I didn't realize that by the time I had cut it down to what I thought was the right length, it was going to bottom out on the front of the crankshaft.

So, I went to install the gear, and the adapter bottomed out.  But I didn't realize it had bottomed out, I just thought it was taking a lot of force to push the timing gear on.  So, I'm cranking away on what I didn't realize was two unmovable objects, and then I notice that, hey, I've been cranking pretty good here, but nothing's moving much.  So I try to back the bolt out, and ... it won't back out, either.  Now I'm panicking.  In addition to the fact that crankshafts are not cheap, there is also all the time that I've put into building the bottom end up, and that will have to all be un-done and re-done if I have to replace the crankshaft, or even remove it for repair work.  Crap, crap, crap, crap, crap, crap, crap!!!

Eventually I was somehow able to extricate the bolt, but when it came out, it was missing about a quarter inch of threads on the end.  I should mention, I guess, that I was using the old harmonic balancer bolt for this, not the new one.  Anyway, it looked like this:

 

So, I'm thinking, crap, I stripped this thing out, but it really looks like the threads just came off the bolt, maybe the threads in the crank are OK, or maybe they can be salvaged.  So I took the new harmonic balancer bolt and tried to thread it into the crank, but it wouldn't start.  So, I went to Harbor Freight and got a tap and die set with fine-thread taps, and I tried to clean up the damaged threads in the crank.  I got it to where I could run the new bolt in and out by hand, although it feels a little tight.  I never ran the tap all the way down the hole, I just cleaned up the damaged threads at the front of the hole.  It's not a very good picture, but I tried to show the threads here:

 

 

The shiny silver threads at the front are the damaged ones, the gold-ish color towards the back haven't been touched.
 
So next, I did one of the things that I should have done in the first place and went down to Auto Zone to rent their harmonic balancer installer.  It has short adapters to fit different crankshafts, and a long bolt that threads into the adapter, and then a larger tube which is threaded on its outside, and which the long bolt runs down the middle of.  So you mount all that to the front of the crank, and then there's a nut threaded on to the larger threaded tube, and you run that nut down to pull the harmonic balancer (or crank timing gear in my case) on to the crank.  There's a bearing that goes between the nut and the balancer, too, but you get the idea.  Also, I still needed to make an adapter out of a new piece of pipe, but the extra length of the installer tool allowed me to make the adapter long enough so that it wouldn't bottom out.

OK, so anyway, the adapter for the installer tool has less thread length than the harmonic balancer bolt, as you can see here:

 

 

The adapter was going to be mostly grabbing the damaged threads, so I thought, well, this will be a good test to see if those threads are good for anything at all.  So I set it all up, started turning the nut to install the timing gear, and the whole installer tool was turning.  I thought it was turning in the damaged threads, and I thought, "crap, those threads aren't doing anything at all, they're junk, I'm screwed."  But, there are flats on the tool, so I tried putting a wrench on there to try to stop it from turning, and then I was able to use it to run the timing gear down.

HOWEVER ... I realized later that I was wrong ... it wasn't that the installer tool was turning in the crank threads, it's that the large threaded tube on the installer tool is just clamped between the long inner bolt and the adapter, but it isn't really secured to either one very well.  That's why they put flats on it, because if you don't put a wrench on the tube, it will just spin around the inner bolt.  I would guess that is by design, so that you are not transmitting any torque to the adapter, which might strip out otherwise.  Smart design.  Stupid operator, but smart design.

I'm getting ahead of myself a little bit, though.  My original thought was that it looked like there were a lot of good threads behind the damaged threads, and that maybe a longer bolt could reach back and engage more of those good threads.  So eventually, after messing around with some other of this other stuff, I started trying to figure out what was the longest bolt that could fit into the hole, so that I could use as much thread as possible if I could find a longer bolt.

After taking a lot of measurements, I decided that there isn't even room for another quarter inch of bolt length.  You might be able to fit 3/16in., but not any significant amount.  So then I thought, well, what's my thread engagement right now, and I measured that out and decided that right now the bolt should be engaging about .515in. of good threads, plus another 0.2in. of the damaged/repaired threads.  I looked up an online calculator for minimum recommended thread engagement, and it was saying that for this size bolt, minimum thread engagement should be somewhere around 0.45in., which would mean that at .515in., I'd have more than the recommended minimum just with good threads, not even counting the repaired threads, which I think are also doing some good.

So basically, after all that and everything else, I've decided that I am OK just using the bolt I have in the crank as it is.  So, most of the money I saved by not buying the recommended tools went into buying the tap and die set.  But, when you consider all the money that I saved by shortening my life by a couple years through anxiety and worrying over the damaged crank, I still came out ahead.

 

Anyway, during that same week, my roller cam button showed up.  Now we're back on track.  Eager to make some progress, the next weekend I sat down with my instructions again, and I read a section that I somehow missed the three times that I previously looked through the instructions.  It explains about how the stock stamped steel timing cover is too flimsy to locate the cam accurately, and you really should get a cast aluminum or otherwise stiffened timing cover.  Son of a gun, seems like I've heard something like that before ... somewhere several paragraphs ago....

So, I look through a bunch of aluminum timing covers, and eventually order one that seems to be the best mix of not-too-pricey and not-too-flashy.  I didn't really want a lot of aluminum parts on the engine, but at least there's a good reason for this one, I guess.

I guess I should also mention that somewhere along the line with all this other stuff, I tried to put the cam timing gear on, and I found that it wouldn't go on.  It felt like the locating dowel was a press fit, but I was pretty sure it wasn't supposed to be a press fit.  I think that, far and away, the best thing about Comp Cams is their tech support.  I mentioned in an earlier post about how I filled in their forms to get a cam recommendation, and I was contacted by an actual person with whom I was able to carry on a dialogue.  Customer service.  What a crazy concept.

Well, ever since then, even months after the sale, if I have a question, I can e-mail that same guy, and he will get back to me quickly (often less than an hour, but always within a business day) with an intelligent and helpful response.  So, I asked him, hey, is this cam gear supposed to be a press fit?  He said no, they must have put the wrong dowel in it.  So, we went around and around on options, but eventually I decided to just open up the hole in the cam gear a little bit with a rat tail file.  He said that would be fine.  He even said that he has run cams without a dowel, the main purpose of the dowel is just to make it so that you can't put the gear on in the wrong orientation.

Anyway, eventually my aluminum timing cover showed up.  I went out to the garage on Saturday to test-fit the cam button with the timing cover, and ... the timing cover wouldn't even bolt up to the block with the button in place.  It wasn't even close, either, it was almost a quarter of an inch away from the block.  So, I decided the thing to do is to find a machine shop that can remove some material from the cam button and the inside of the timing cover, to bring cam endplay into spec.

While taking measurements to try to determine how much material to remove from each part, I noticed that the cam timing gear is about 0.010" back towards the block from where the crank timing gear is.  So, there is a company that offers a thrust washer to put behind the cam gear, where it bears against the front of the block.  The cam gear needs to be machined to accommodate that thrust washer, but that works out well, because right now my plan is to put that thrust washer behind the cam gear, then get the gear machined by 0.010" less than the thrust washer's thickness, to bring the cam gear back in line with the crank gear.

At the same time, I'll get the same shop to machine about 1/8" off the cam button's length, and about 1/8" off the inside of the timing cover.  That should put me close on camshaft endplay, close enough that I can assemble the parts and measure it.  Then if I am over the endplay spec, I can measure how much I'm over by and get that thickness machined off the mounting flange of the timing cover, to bring it back towards the block and tighten up the endplay to bring it in spec.  That would also help if I end up having to run a 1965-style short water pump, instead of the 1972-style long one that I am used to, which will be a whole other thing ... but, one thing at a time....