Camshaft timing

B0b

B0b

Daily Driver
Finally got the block back, and am setting up to check piston/valve clearance and to decide what to do with the head.
Checked the cam pulley timing mark, and found it to be off, but I'd like to check my method.
The timing diagram for the cam looks like this ( by measurement, at 0.5mm clearance):
cam timng.PNG
From this, I set TDC at 180 degrees from the midpoint between the maximum opening of the intake and exhaust lobes - in other words splitting the lobe separation symmetrically about BDC.
Using the new mark, and with the engine dry assembled without a head gasket, the timing is about 1.5 degrees retarded. With the head gasket in place, the timing is within 0.5 degree.
I left off the head gasket to simulate shaving the head,
Interestingly, the belt tensions just fine, using about 60% of the travel.
These results seem to be a bit at odds with what others have found, and I wonder if I am missing something.
 
If I'm understanding correctly, it seems that you may be experiencing the all too common issue when too much material is removed from the head and/or block. This throws your cam timing out. An adjustable cam gear will get you dialed back in.
 
Bob, I may have misunderstood what you did so the following might be redundant - if so please ignore it.

Try using the degree wheel to find TDC of the cam and compare that to the TDC mark on the flywheel. That will tell you if your marks are off somewhere. Also keep in the mind the front pulley is not a good place to determine TDC, as the pointer is adjustable. So the flywheel mark is better, provided it isn't 180 degrees out (which can easily happen).

Otherwise the cam timing will change with differences in head/head gasket thickness. The tensioner may still allow sufficient tension (depending on how much is removed from the head), but the actual cam timing will be off despite the tension looking good. As "Eastep" said, that's where an adjustable cam gear comes into play.

Please let us know if we've completely missed your question.
 
B0b said:
With the head gasket in place, the timing is within 0.5 degree.
Click to expand...
.5 degree is pretty much the limit of accuracy of these measurements, so you're doing fine. It would not be totally amazing to find that when one cylinder is spot on perfect (center of cam overlap, halfway between intake opening and exhaust closing, is at exactly TDC) the others are out by as much as one-half degree.
 
I didn't explain it well. I understand about adjustable sprockets, etc.

Using a degree wheel, I determined the TDC on the cam, centered between the lobe centers.
I am using an aftermarket cam sprocket, and the timing mark is not accurate, at least for the 4331512 cam I am using.

The head is not modified - I am working on deciding what I might do.
That includes removing material to get rid of some or all of the 2mm deep recess.

By leaving out the head gasket, it simulates removing 1.5mm or so from the head, so I could check to see what the valve to piston clearance would be.
I am using pistons with a larger compression height and was concerned that the valves might be too close to the pistons, in which case I'd deepen the piston pockets. Lots of clearance, however.
At the same time, I checked to see what affect removing 1.5mm would have on the timing, and it retards the cam by 3 crank degrees.

I understood from other posts that removing 1.5mm or more from the head would create tensioner travel issues, but I didn't see that effect.

As mentioned, I thought there would be a bigger tensioner problem, hence the query abbout whether I might have missed something.
Also, is the timing retardation of 3 crank degrees with decking the head 1.5mm consistent with what other have seen?

Guess I am just looking for whether or not these numbers seem reasonable before I make the next decisions.
 
Have you checked to see if you have a 1300 or 1500 tensioner? A 1300 may explain why you don't have a problem with the tension.
 
Hi Bob,

4331512 isn't symmetrical.
sohccamspecs 128 rallya.jpg


24/68 64/28 puts the lobe centre of the intake at 112 ATDC and the lobe centre of the exhaust at 108BTDC... if you simply spit the difference then your TDC mark is off.

Running out of tensioner movement issues are when people machine away the decompression recess from the head face AND also machine the cambox to use a cam of a reduced base circle and not have to run 6mm shims, all you were simulating was machining the head.

TDC markings on the yellow plastic cover cannot be used as an accurate reference point for cam timing. You need to use the flywheel dimple. If you've machined that away when lightening, then you need to mark it again, as the flywheel / bellhousing are the most easily accessable and accurate marks.

An optional mark exists on the front toothed crank timimg gear, you will find a machined in scribe mark, this lines up with a cast in nub on the front alloy seal carrier, not 100% accurate as the diameter is very small, flywheel is far more accurate due to the much larger diameter.

My method.

Mount the flywheel to the crank, use a transmission bellhousing and bolt this to the block, bolt all this to the engine stand.
1300 flywheel has 120 teeth, handy, as each tooth is a pretty accurate way to measure off 3 degree increments.

You must determine TRUE TDC. I use whats known as the "positive stop" method. I have a flat piece of sturdy steel, it has a drilled / threaded hole in the middle (more or less) and bolts to the top of the block, so the threaded hole is close enough to central, into threaded hole is a bolt which exends thru the plate and into the cylinder by a small margin, maybe 10mm. Wind the crank over until the piston contacts the bolt, mark off the flywheel, wind it back in the opposite direction until the piston again lightly contacts the bolt, mark this off... exactly half way is true TDC. Why is this the best method? as it removes the dwell period the piston has at the top of it's stroke, which makes it very hard to accurately gauge TDC to within a small margin of error...

Cylinder head. Why are you bothering with the original early style combustion chamber head? Yugo 1300 head would be the go to unit in your case as it has the later style combustion chamber, no full circular decompression recess, and is basically the same as the later european 1300 heads. Find one of these and spend the time and effort on that, much better return for your efforts.

The rest of the papaer build is good, piston position, SQ, CR, V/P clearance are all being measured/considered and you're on the right path.

SteveC
 
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Thanks for the comments.
I completely missed the assymetrical timing - adjusted for that and remeasured everything.
I verified the crank nose and flywheel tiing marks using a dial indicator instead of a dead stop, stopping 1mm either side of TDC and splitting the difference. The marks are quite close. Interestingly the clearance between the flywheel bolts and the holes in the flywheel allow for a bit of adjustment. I expected dowels so at final assembly the flywheel position will need to be set before torquing.

With the cam timing set correctly, the piston to valve clearance is still OK, checking without a head gasket, so I can deck the head substantially without worrying about clearances.

I definitely have a 1300 tensioner - its a 1300.

Why the north american head - its what I have, and since this is a more or less original 1974, the only real mod planned is changing the cam and maybe upping the CR.
With the new pistons, there is positive 0.075mm deck, and with the increased displacement (87mm bore) and a measured head volume, I calculate a CR of 8.8.
If 0.5mm is removed from the head, the CR goes to 9.5, and the effect on the cam timing is minimal.
As I see it the alternative is to take 1.5mm off the head, then remove about 5 cc of material from the combustion chamber, lowering the CR down to 9.5 or so, and unshrouding the valves. This would also reduce the SQ from about 3.5mm to 2mm.

In a mild state of tune, ( cam, 32 DMTR carb) will there be a substantial different between the two options?
I understand the theory, but practically is the difference measurable?

I don't mind undertaking the work on the combustion chamber, and might decide to do it just for fun, but any reality check on the benefit would be welcome.
 
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B0b said:
In a mild state of tune, ( cam, 32 DMTR carb) will there be a substantial different between the two options?
Click to expand...
If you consider the very low output of these engines, minor changes are not likely to make a significant difference in my opinion. To put it another way, if a modification gains you a 5% improvement (which is much more that I'd expect here), that will be something like 3 HP. You'd be better off losing 10 pounds, that might make a bigger difference on the total performance. Personally I would look at what modifications will yield the most reliability and drivability every day.
 
I think a significant low cost improvement would be to find a working 1500 motor and stick it in. I went from a 1300 to a 1500 using the same intake, exhaust, cam, ignition, etc. on both and there was a pretty noticeable difference in torque. I'm running a cam slightly hotter than yours and I found that unless you are going fast enough to be on the torque curve (>4K), slight hills would require downshifting from fourth to third. The 1500 seems to have enough extra torque to keep this from happening to the point where I'm not even considering a 5 speed.
 
Thanks for all the improvement suggestions, but this X1/9 is, as I mentioned in an introductory post, connected to the one I bought in 1974.
I have had a solo event car, stripped, with a hot 1500, a stock injected 1500, and a turbocharged 1300, and am not looking for this car to be anything other than a pleasant ice cream getter.
Got other things to go fast in.
At the moment I think I will just take 0.5mm off the head, and leave worrying about valve shrouding, SQ dimensions, etc. for another time.
However, the whole winter lies ahead and boredom might lead to doing some head work.
 
dllubin said:
I'm running a cam slightly hotter than yours and I found that unless you are going fast enough to be on the torque curve (>4K), slight hills would require downshifting from fourth to third.
Click to expand...
Although my comment does not necessarily apply to Bob's build, the point that Don mentioned is something I firmly believe in (however I'm not saying this was Don's case, just making a related comment). It is very easy to get caught up in the excitement of building a performance engine and want to go further with everything - project creep if you will. The tendency is to want a bigger cam, more compression, multiple carbs, race header, big ports, and everything else that makes power. However what you end up with is an engine that isn't very drivable on the street. Race engines (which is what it becomes) are not friendly in stop and go, normal traffic, legal speeds, city driving. And having to buy high octane fuel, deal with fussy carbs, worry about overheating, and frequent repairs is no fun....which is the whole point, to have fun. In my opinion building a conservative reliable engine that has loads of torque in the lower RPM's (which is where a street engine spends most of its life) is much more fun to drive anywhere other than a track. Again, I'm not implying anyone here has fallen victim to this temptation - only expressing my opinion. And it sounds like this is what Bob's intentions are, to have a nice driver rather than a track car.
 
A little cam, a little compression, a little carburation (OK, two of 'em!), a little ignition, some exhaust, etc...and the SOHC engine wakes up nicely. That "little work" helps turn the X1/9 into the kinda car that puts a smile on your face! It's a night and day difference.
Yes, you can go overboard, but make no mistake - Fiat tuned the stock engine for emissions. Some basic hotrodding transforms the car. It doesn't take much to wake the car up, you don't need 200HP to have a really fun car.
 
MikeHynes said:
A little cam, a little compression, a little carburation (OK, two of 'em!), a little ignition, some exhaust, etc...and the SOHC engine wakes up nicely. That "little work" helps turn the X1/9 into the kinda car that puts a smile on your face! It's a night and day difference.
Yes, you can go overboard, but make no mistake - Fiat tuned the stock engine for emissions. Some basic hotrodding transforms the car. It doesn't take much to wake the car up, you don't need 200HP to have a really fun car.
Click to expand...
In fact, just bringing the early cars into stock European trim (compression bump from losing the milled recess, 4/2 exhaust, a bit more cam, rejet to Euro) makes a fun car, with no streetability compromises. You’re just getting the Euro compromise between performance and emissions instead of the American.
 
MikeHynes said:
A little cam, a little compression, a little carburation (OK, two of 'em!), a little ignition, some exhaust, etc...and the SOHC engine wakes up nicely.
Click to expand...
EricH said:
In fact, just bringing the early cars into stock European trim (compression bump from losing the milled recess, 4/2 exhaust, a bit more cam, rejet to Euro) makes a fun car
Click to expand...
Exactly, a "little" or "Euro spec" are great. I was referring to the common tendency to go beyond a little, and follow the "if a little is good, then a lot must be great" philosophy. ;) In some areas it can be a fairly fine line between a little and too much.
 
Sometimes one just gets lucky.
Finished setting the cam timing today, and much to my surprise the new (1512) cam lined up to within a degree without an adjustable sprocket.
I did replace the original cam sprocket with an aluminum one from Vick. The timing mark on it is in more or less the correct spot but I ignored it.

My engine stand won't accommodate the flywheel, so I used the front pulley. I printed a degree wheel what is the same diameter as that pulley, glues it on, and then determined TDC using both a dial indicator method ( before the head was installed) and a dead stop method (a modified spark plug) after the head was installed. I made up a temporary pointer attached to the block, and set it to the TDC marks on the pulley.
Then I used a dial indicator on the #1 intake valve bucket to find the center of the lobe, and locked the cam in place.
Much to my surprise the timing belt lined up perfectly, and there is enough tensioner travel.
BTW, I wound up taking 0.75 mm off the head.
After tensioning the belt, I checked both the intake and exhaust lobe centers; good within a degree.
 
If you want to get really creaped out, check the thread on MIRA about after market cams made improperly such that the cam lobe locations are different for different cylinders!

I'd be curious to hear how you motor runs compared to a stock motor.
 
It doesn't look like I'll need an adjustable pulley.
As far as how it runs, I won't have it back together and broken until until the summer.

After a bit of a false start with the cam, I checked it lobe by lobe, to make sure it is in fact a factory 4331512.
 
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