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MG MGA - Moss Adj Timing Kit

Hey everyone, I just picked up one of those nifty ajustable timing gear kits. It's the one with the crank gear having multiple keyways.

Unfortunately it came with out any instructions on how to set up the timing.

Has anyone any experience using one of these and/or any suggested reading on getting everything set correctly the first time?

Thanks!
JohnB

I have the same set. There are many websites and books that tell you how to degree a cam. I think I used one of the "How to Build and Power Tune" books. My new cam came with a card that had the suggested install degree. I followed the procedure for locating the crank, locating desired cam lift, via a dial indicator, and then placed the gear set on. In my case, the keyway that lined up was 0°. I believe mine had slots for +4°, +2°, 0°, -2°, and -4°. The idea being that you can adjust where you want the power.

My cam was a Crane 342-0010, which says, "This camshaft is ground 1° retarded for best lobe size and hardness. Optimum performance will result from installing the cam 5° advanced, as indicated on the timing card." I've never been sure what exactly they meant by that because after fitting it at 4° total advance, it still lined up at 0°. I called Crane, assuming the cam was a regrind, hence the directions. They said it wasn't, but I'm still not sure. I felt like the gear set was a waste since after the cam was set, a standard (cheaper)gear set would have worked. Anyway sorry to ramble. Don't be surprised if you have the same experience, where after setting the cam 0° lines up.
Kemper

I have one of those sprocket sets. It is simple in theory, but takes a little fiddling to get a good intuitive grasp.

Set the sprocket up with the "0" keyway on the key, which is the same as a standard crank sprocket. Mark the position of one tooth carefully on a fixed reference surface, or fix a mechanical pointer near the tip of one tooth. Pull the sprocket off, rotate it to the next keyway marked "+2". This is approximately one tooth rotation, except with a slight offset of 4 degrees, which will be about .090" clockwise displacement at the tip of the tooth.

Keeping in mind that the crank sprocked has 20 teeth, and the cam sprocket has 40 teeth, this 4 degrees offset of the crank sprocket makes only 2 degrees offset of the cam sprocket with the chain installed, so that keyway on the crank sprocket is marked "+2" for the change in cam timing. This moves the cam 2 degrees clockwise (advanced).

Unfortunately that Crane cam wants to be indexed from minus 1 to plus 5, which is a total of 6 degrees required advance, and you can't get there using that sprocket set in the manner described.

There is another approach. Since the cam sprocket has 40 teeth, you skip the timing chain over one tooth to advance the cam 9 degrees. Then use the indexing crank sprocket to bring it back 2 or 4 degrees to a net advance of +7 or +5. This is not perfectly +6 but may be close enough. When you get within 1 degree it's time to bring out the degree wheel and dial indicator to see where the cam actually sits.

If you're still a bit picky after that you can buy offset cam keys to make additional adjustments in 1 degree increments. But once you figure out how to do that, you may discover that you don't need the fancy adjustable sprocket.

Using various offset cam keys you can move the cam in 1 degree increments from 0 to 4 plus or minus for a total range of 8 degrees. Skipping the chain over one tooth on the sprocket makes 9 degrees, and you can then repeat the entire sequenbce with the offset cam keys, allowing cam timing in 1 degree increments all around the clock.

But it can be even simpler. If you can tolerate up to 1.5 degrees maximum error at the camshaft, you can do this with one straight cam key and one offset key for 3 degrees change, and you can walk it around the clock in 3 degree increments.

By coincidence, 3 degrees at the cam equates to exactly 1/32 inch offset of the cam key. If you might have a milling maching hamdy, or maybe know someone who does, you're in luck. You can take a crankshaft key which is 3/16 inch thick, and mill a 1/32 inch step off each side to make a cam key 5/32 inch thick with 1/32 inch offset. This might seem like a bit of a pain, but if you can do it on the spot and get the engine back together immediately it may be worth the effort.

Also don't forget you may need to cut clearance eyebrows in the block to accomodate the increased valve lift with that camshaft. And you probably want uprated valve springs to prevent valve float at 6000 rpm (which will otherwise happen with the increased lift).

Additionally the new tappets you MUST have to go with the new cam may be changed to the later issue short bucket tappets from the 18V engine, which are much lighter than the original tall tappets. Then also include a set of the longer pushrods from the 18V engine.

And here you thought that new cam was going to be a simple bolt in affair, huh?
Barney Gaylord

Not to steal the thread, but now I'm worried. I understood it from Crane that the cam was ground at -1° so they wanted 5° added to get a net of +4°.

It's been a long while ago since I did this and I recall I got a few opinions on where the cam should be. It was the first time I'd done an adjustable cam, too. As I recall, I added the 5° to the max intake lift degree on cylinder 1 to get the crank degree and then fitted the gear set. That engine is on the shelf still and I have a feeling I'll open it up again to be sure.
Kemper

Not too put too much of a dampener on the whole debate of offset keys, but a friend used these and broke the key whilst flat changing during a day drag races.

Whilst most people won't try this, it does create a weak point however, so ensure you have a good fit and you tighten up the cam nut sufficiently, possibly use loctite also.
I prefer the much more expensive vernier cam gear.
Tricky business getting the timing right, I have a long solid piece of bar the fits into the pushrod hole, which makes things easier.
Cheers <MARK>
Mark Hester

Kemper,

Read the Crane timing card again. Ground -1. Best results at +5. You need to advance it 6 degrees. I have installed several of these. The timing checks out to match the timing card when indexed 6 degrees. Don't assume you have it right, and don't quit until the cam timing matches the numbers on the card.
Barney Gaylord

This thread was discussed between 19/01/2006 and 20/01/2006

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