Engine rebuild

[ORFORD2004]

You better remove the rad to have a straight view.

[phaetn]

Yes, thanks. I'm planning on doing this when the engine is outside of the car.

So what is the measurements I am looking for in on the intake and exhaust cams? 110 degrees on the intake? I am using A/R's reground intake with the following specs (form their site, not my measurements):

40/80 exhaust reground camshaft
10.1mm lift, 240 degrees duration at .050" (1.25mm) clearance
Lash clearance 0.012" (0.30mm)

The machinists ground the stem of the valves to get .017-.019 valve clearance as that was what they read in the shop manual. I see this says a lash clearance of 0.012. Is this the clearance I should be seeking? If so I might be struggling to get the right shims. I think Volvo used the same type.

Finally, do I have to measure the travel for each lobe of the intake cam with the dial indicator and then "average out" the results to find the best cam pulley position, or if I do it once it should be fine since the relationships between cams are all fixed (albeit values may depend in the skill of the grinder)? Or, in fact, am I measuring all to find a happy medium for that particular cam?

Thanks for all of your support!

phaetn

[Nut124]

110 centers on both IN and EX should work fine.

When I degree my cams I only measure #1 lobe.

[18Fiatsandcounting]

The machinists ground the stem of the valves to get .017-.019 valve clearance as that was what they read in the shop manual. I see this says a lash clearance of 0.012. Is this the clearance I should be seeking? If so I might be struggling to get the right shims. I think Volvo used the same type.

Phaetn, 0.017" for the intake and 0.019" for the exhaust is the spec for the valve shim clearance, although the spec was originally in metric (0.45 and 0.50 mm). Some people do run tighter clearances, but my feeling was this was always a bit risky because if the clearance is too low, you could run the risk of a valve not fully closing when it should. But, I also trust AR, so I'm not going to dispute what they recommended. If it were me, I'd give them a call and make sure all is good.

Note that these tappet shims are available over a wide range of sizes, so it's hard to imagine that you could get into a situation where you couldn't find a needed thickness. Shims are available from roughly 2.5 to 5 mm thicknesses in steps of 0.05 mm, as I recall.

If your shims need to be outside of that range, something else might be amiss.

-Bryan

[Nut124]

Regarding valve clearance. I'd go with what the cam maker/seller specifies. Modern performance cams for the Fiat TwinCam use 0.008/0.010 clearances.

The clearance actually increases when hot, rather than decreasing.

The clearance affects valve closing velocity. Too much and the valves hit the seats at high speed causing noise and possible seat, valve damage. Too little and cam duration is increased, kind of. However, increasing duration this way hurts performance more than it helps.

[phaetn]

The machinists ground the stem of the valves to get .017-.019 valve clearance as that was what they read in the shop manual. I see this says a lash clearance of 0.012. Is this the clearance I should be seeking? If so I might be struggling to get the right shims. I think Volvo used the same type.

Phaetn, 0.017" for the intake and 0.019" for the exhaust is the spec for the valve shim clearance, although the spec was originally in metric (0.45 and 0.50 mm). Some people do run tighter clearances, but my feeling was this was always a bit risky because if the clearance is too low, you could run the risk of a valve not fully closing when it should. But, I also trust AR, so I'm not going to dispute what they recommended. If it were me, I'd give them a call and make sure all is good.

Note that these tappet shims are available over a wide range of sizes, so it's hard to imagine that you could get into a situation where you couldn't find a needed thickness. Shims are available from roughly 2.5 to 5 mm thicknesses in steps of 0.05 mm, as I recall.

If your shims need to be outside of that range, something else might be amiss.

-Bryan

Thanks! Because I'm using a reground cam the base circle is off compared to a stock cam or a brand new one and it therefore requires compensation (thicker than usual shims). I was doubly a fool as i) I didn't order A/R's top hat shim / lash caps that fit under the bucket to take up 1.65mm of clearance when I ordered the 40/80 performance cam (blinded by dreams of power, I suppose); and ii) I gave the machinist stock specs for valve lash rather than what was published on A/R's site for this cam.

As I understand it, keeping a stock clearance would mean not taking full advantage of what power the cam offers as the valve doesn't open fully so a bigger shim = free power to a point -- can also lead to bent and maybe even burnt valves, though.

The machinist used .200" shims (5.05mm) to get to stock clearance. I figure if I use 5.20mm shims (.015mm=.006") -- the max size available from A/R -- then I should be able to get to 0.012 lash assuming they are currently at around .018 lash. I'll have to go out to my buddy's tomorrow with a set of feeler gauges to actually measure what's what... I've sent an e-mail to Csaba to verify the clearance.

Looks like there will be a delay in getting it on the road until I sort this out...

Cheers,
phaetn

[18Fiatsandcounting]

Gotcha Phaetn, and I had forgotten you don't have a stock engine in terms of cams. Yes, carry on, and I suggest listening to Nut124 rather than to me as he's much more experienced in this area than I am.

Bryan

[Nut124]

It would be a small miracle if all the shims in are the same. I'd ask the builder for a record of each shim thickness. Cannot order correct replacements w/o knowing what is installed.

I doubt that you would notice any difference in power between 0.016/18 and 0.010/12. The bigger clearance costs you 0.006" of max lift or about 1.5% plus a few degrees of theoretical duration. Unless you hear excessive valve noise it might just be fine as is.

Below is a lobe profile measurement and calculated valve closing velocity for a CAT301 cam. The target velocity is less than 1.25 thou per cam degree. The clearance spec for this cam is 0.010" which is in line with the velocity rule.

[phaetn]

Thanks, Nut124. That's all Greek to me (that's Shakespeare, which I do understand).

I get the overall point, if not the details. It's not like I'm building a modern racing engine with minuscule tolerances so I think it will be fine. I don't have a record of the shims used, but the machinist did use a micro and was aiming for .200" shims (5.05mm). I saw him measure them and he picked the four thickest which must all have been within a certain range. They ground the valve stems to suit and, according to my buddy, were given the spec .015 lash. That's what he says he told them, but I had told them differently. So I don't know what was actually used and I have yet to confirm this for myself (didn't make it out yesterday) -- it's a communication issue, really, which is really at the heart of most concerns.

Csaba confirmed a few thou. won't make much of a recognizable difference to power. We'll pop on the head as-is and then will re-shim later once it's been run-in. I've ordered both the top hats (go under the bucket and add 1.65mm) AND thick shims from 5.00 to 5.20 range in .05 increments, x 4 for each. I'll be able to use either (both not both, obviously); I would rather save the step of cleaning out the oil and taking off the cam tower since it's already all buttoned up so will just use the shims. I'll save the hats for the future. Maybe if I eventually go for an exhaust cam, too. I'll have learnt my lesson by then.

Thanks everyone. What a terrific community!
phaetn

[phaetn]

So things are coming along: transmission installed and head installed, with intake and carb.

Took some early readings to dial in the cam but ran out of steam so I'll go back to it another time.

Looks like I will be able to run the stock oil pressures sensor and warning light from one port using a bypass, and then be able to use a 1/8NPT fitting for new gauges (elec. pressure, temp, mechanical pressure).

Cheers,
phaetn

[RRoller123]

NICE!

[phaetn]

NICE!

Thanks! To be honest, in present form I kind of feel like strapping a seat to the transmission and make some sort of rocket or hover bike out of it, but that's wishful thinking. I do miss my '72 Honda CL350K4 that I modded into a café racer, but that was a few years and about 10lbs ago.



No regrets that I sold the bike it as the temptation would have been too great to ride it and I probably never would have bought the Spider!

Update on the cams: I finally got a dial indicator set up borrowing a friend's magnetic base stand, using a piece of steel L bracket affixed to the cam tower cover stud to act as a mount for the magnet. I used a nail taped to the plunger to get something narrow enough to touch the tappet but not interfere with the cam. It took a lot of time to get it close to right but in the end I wasn't that comfortable with the readings so called it a day. I had a very precise true TDC (having used the the dial indicator threaded into the spark plug hole) and used that to eyeball the adjustable cam pulleys to the cam tower casted marks. I ended up having to use the intake and exhaust pulley adjustment to make the belt fit just right as it was off about half a tooth otherwise.

I know it won't be as precise as a truly dialed in cam but I need to get this back in the car and started. Once parts are seated in I'll go and replace shims to get appropriate lash clearance to the intake as it was much too high (limited by the shims the machinist had at the time).

The plan is to get the engine back in this weekend.

Cheers,
phaetn

[RRoller123]

Then you will be playing with the adjustable cam wheels anyway, so the most important thing is just to be sure that you know exactly where the starting point was, so you always have a datum!

[phaetn]

My mechanic buddy -- who has torn down and rebuilt more of these than anyone else in town -- says he can use vacuum gauges to get best settings. Not sure how that will work. It would seem to me that would be about the relationship between intake and exhaust cams rather than setting each in isolation.

I might dial it in later as a summer project when in-situ. On my car it's very easy to pull the rad and there's lots of space to view the crank pulley.

Cheers,
phaetn

[Nut124]

Do not give up now. You are so close.

The only way to reliably set cam timing is to do it the way I tried to show. Anything else is guess work.

Most dial indicators have a threaded sleeve at the tip. I removed the sleeve, then made a new sleeve with a longer thru thread. I threaded the new sleeve to the indicator and then epoxied a long steel rod in the threaded hole. This indicator stem extension must be solid for the measurements to work.

TDC must be accurate as well.

You do not need to degree the entire profile. If you could just get a few reliable measurements at both opening and closing, like 0.010, 0.020, 0.050. That would do. More would be better. Each pair will give you a C/L number, which you can then assess for consistency. More pairs will improve accuracy assuming there is no systemic error.

In my picture below, the OPEN and CLOSE data are on the left. The resulting C/L calculation is in the "Lobe CL" column. You can see how consistent the CL values are, except for the 0.010.