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Cam degreeing questions

How to Degree a Cam

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Discussion and questions related to the course How to Degree a Cam

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1. During degreeing a cam, should I set the valve clearance to the stock clearance, cam card clearance or make sure no clearance exist between lifter and valve?

2. If I accidentally went over the 1mm lift point, can I just back up to the 1mm lift point or do I have to go a little bit further back, and then moving forward to the 1mm lift point? Or do I have to start over?

3. Is taking out the spark plug during degreeing process a good idea? Without the spark plugs, no compression will be generated thus makes for an easier turning of the crankshaft.

4. When measuring for valve and piston clearance, is there a limit on how much is a safe gap between the two or can I put the highest lift cam as long as the valve didn't touch the piston? Especially in high RPM condition where valve floating is a concern. In the course, Andre just demonstrate how we can measure this clearance but didn't go into how we can actually tell that the two has enough distance.

5. How do I degree a cam that does not come with a cam card? Do I need to have some dyno time?

6. In many engines that I build, it is necessary to unbolt the cam sprocket in order to take out the cam and lifter. In this case, how can I take out the temporary solid lifter to reinstall the original hydraulic lifter?

7. There should be a PDF file for this course as mentioned by Andre, which I cannot find. I didn't remember which module it is though.

8. There are two methods of adjusting the cam timing. One is using the adjustable vernier that needs to be tighten with Allen bolts, the other one is by changing the key slot on the sprocket. Please explain the process for the adjusting cam timing on multiple key slots sprocket. I can't visualize how several key slots can make for fine adjustment.

9. If I find the true TDC on an engine without adjustable cam sprocket, how can I go to use this true TDC point instead of the original crank timing mark? Can I use the 0° mark on my degree wheel as my new crank mark?

NOTE, my thoughts and opinions - others may have different ones and it's your responsibility to check, especially as you'll be paying the repair bills ;-)

1/ Depends, different manufacturers have different techniques - use what they recommend.

2/ Just back of a little further and bring it back up to the mark. One small caveat, though, there are some rare engines where the camshaft tensioners don't like to be reversed, so if you have one of those rare andgines, just wind it through a little less than 2 revolutions and bring it up to the mark. The reason is is bad practice to just bring it down to the mark is that there are tolerances in the valve train and they can be significant and normal rotation already accounts for them

3/ Spark plug removal is normal practice, as it does make everything that much easier

4/ While in theory, you 'just' need to clear them, in practice there are multiple things to consider, as you surmise. You will usually find the camshaft supplier will give a minimum figure for the intake and exhaust. I hesitate to suggest a minimum if there isn't one given - anyone - but 2mm inlet, 2.5mm exhaust 'should' be good. I have run them quite a lot tighter, but it can be risky and if it's too tight it'll often take out the entire engine - block, head, crankshaft, camshfts - everything!

5/ Any camshaft from a repurtable supplier should have a card. If there isn't one, have a careful look over the camshaft(s) for any identification - it's usually on the end opposite the gear/pulley - and from that you should be able to get the information on-line. If even that is missing, I'd suggest not using it/them, but if you really want to, install it to the same centre line as the OEM and check clearance there and with it advanced and retarded so you're confident of valve-piston clearances - you should be using vernier gears/pulleys - and then you can fine tune them on the dyno.

6/ Don't look at it as a task to be avoided - for serious builds it isn't unknown for them to be trial assembled several times for checking clearances, tolerances, timing, etc. before rings are fitted and the final assembly is completed, and you can set the timing during those. If it's a completed engine, and you're doing a simple check and fit, then the hassle is just one of those things.

7/ Sorry, can't help there.

8/ It's a bit more complicated than that with three variations I know of - I'll try and summarise them so you can check on-line for better explanations. the first type, which we'll call a/, is a simple two piece gear, or sprocket, with one part fixed to the camshaft and one which it turned by the chain, or belt. this will usually have a main mark on one that is aligned with marks on the other to adjust their relationship. Some, which we will call b/ have a series of marks on each, that have spightly different spaces for each and the timing is adjusted by lining ut one mark on each - this is an actual vernier (this is the first thing to look up, as the principle is so simple, yet complicated) and can give a more accurate adjustment. The third variation, c/, uses a series of drilled holes in each, which are aligned with a pin - some like this because they're physically locked together and the timing can't slip. There is even a third type, which has a single hole in each and a special pin is used that has an offset of the ends, and different pin offsets.

Then there are the single piece sprockets/pulleys. These will have several holes, or key slots, which will slightly offset the position of the teeth to the camshaft as the different ones are used. This is better explained on-line, but basically is you have a 36 tooth pulley, and 5 holes/ slots, you can have the middle slot position a tooth at, say, TDC, but the slots before and after can be used to offset different teeth to, say, 2 degrees and four degrees BTDC and ATDC, then when the sprocket is moved to the TDC position the camshaft is rotated that amount, advancing or retarding it.

They don't seem so common nowadays but, in times past, there is another method that can be used - offset woodruff keys. These were specially machined with a slight offset between the part that slipped into the shaft groove and the part that the gear slid over. Back in the day adjustable sprockets were unavailable, very expensive, or banned for some race classes so they were used to correct, or tweak, the camshaft timing. OEM manufacturing tolerances are much, much better nowadays, but I expect they still have a place in some restricted race classes.

9/ If you have the true crankshaft TDC and the camshaft timing check shows it to be a little out, your only real alternative to a vernier will be the offset keys I mentioned above - they are available for quite a wide range of engines, more if you know what you need. Normally they're used at the camshaft, but they can be used at the crankshaft, if needed for the application.

No, the crankshaft is the crank shaft, and the camshaft(s) are the camshaft(s). Depending on the engine, you may be able to purchase adjustable pointers or timing scales, or you may be able to make your own. Whatever method you use, use the true TDC to correct the timing marks you will be using for reference.

Re-read that last bit - yes, when you have established the true TDC using the degree wheel, that is what you will use to set the new crankshaft timing marks.

Hi Gord,

Thanks for providing excellent and detailed explanation. Some of my questions sound dumb now that I give it a little bit more thought.

I have one more question if you don't mind.

8. Do you happen to know the names for those different types of cam timing adjusting hardwares? I would like to do more research and have a better visual understanding on it.

Take care

A simple pulley with single alignment mark, with advice - https://www.youtube.com/watch?v=jXdhrqFy1nA

Examples of offset dowels - https://www.burtonpower.com/offset-camshaft-dowel-kit-set-of-9-x-flow-pre-x-flow-fp220s.html

Example of offset woodruff key, works the same way as dowels - https://www.mopedarmy.com/img/alter/index.php?args=b5714bb454de6ef05a0b246bcdc1bc6a/fit_to_width=800/src/http://www.gomeyer.com/rc-cars-scooters/images/rocket_key.jpg

Example of vernier gears, note the relative positions of the gear teeth to the various woodruff grooves, same principle applies with cam'gears/pullies with multiple dowel holes - https://www.minimania.com/images/articles/C-AJJ3327.gif There were versions made where a two piece pulley/sprocket were used, with the dowel having different positions in one, or both, parts to adjust their relationship, but last one I saw was for a Ford Pinto engine and made by, I think, Farndon engineering and that was quite some time ago.

You may also like to check out the operating principle for verniers - the term is still used, but not really applicable for most designs.

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