Unequal IVO & IVC events

[frnkeore]

Ok, now with the cam card, you have something to work with.

Ignore the ex for now. Set the in cam at 110 and check your lift and timing. If it's up to spec, check the ex CL and then advance or retard it, to 110 and check those specs. I've done many TC Cosworth's and I always set the LSA, on one cam first (doesn't matter which), before I check anything else.

If they are not to spec, call the cam company.

[modok]

Duration at .35mm lift
You measure 234
it's supposed to measure 266 according to card

That's way off. Not even in the ballpark.

What do you get checking at 1.25mm lift? Checking at .050 has become the standard worldwide. not sure why you checked at .35, not a big deal, but NEXT time.

[Dairymilkbatman]

OK, so if the clearances are set now to the specified 0.25 mm/0.25 mm, you can adjust your dial indicator to read 0.25 with the valve on the seat, then rotate the engine until it reads 0.35, which is the specified lobe lift for the 266/270 duration numbers. At this point the degree wheel should read 23°BTDC.

Rotating further, until the indicator has risen to its peak (should be 9.35 mm @ 110° ATDC*) and then dropped back down to 0.35, the reading should be 63° ABDC. As long as any errors are symmetrical, say 3° more on each, i.e. 26°and 66° you're good, it just means your checking lift height was minutely off. *If there's a minor discrepancy between IVO/IVC vs. measured centerline numbers, go with the former.

Thanks for the replies, much appreciated, it really is.

I just got 6° BTDC IVO, 51°ABDC IVC

I'll double check peak lift, brb.

[Dairymilkbatman]

Duration at .35mm lift
You measure 234
it's supposed to measure 266 according to card

That's way off. Not even in the ballpark.

What do you get checking at 1.25mm lift? Checking at .050 has become the standard worldwide. not sure why you checked at .35, not a big deal, but NEXT time.

I'll check .050 now too

[MadBill]

Although 0.050" is a near-universal North American cam checking lobe lift, much of the rest of the world uses metric figures and since those are what have been supplied for your cams, I'd stick with mm.

To recap, at 1.25 mm lobe lift the spec is 3° BTDC to 43°ABDC, for a duration of 226°. Your latest figures of 6° & 51°for a duration of 237° tell us that you need to check at slightly greater lift, to bring the measured duration down to spec. Just keep checking the events at small increments of lift until the observed duration equals 226°.

At that point the indexing error will be easy to see, e.g. if you measure IVO @ 1° BTDC and IVC @ 45°ABDC, the cam needs to be advanced by 2°.

[modok]

Bill
1.25mm is .0492
Close enough to .050

[modok]

I think he is not adding the lash from his indicator reading.

If the engine is set at .010 lash, then the indicator should be "zeroed" at .010", not 0

[MadBill]

Yes, I mentioned that a few posts back, but maybe it was missed.
And true, 1.35 mm is virtually the same as 0.050". (actually 0.053" per my conversion program) but I thought it would reduce confusion to keep it all metric. (Didn't think to ask if his dial gauge was metric or imperial!)

[modok]

spec sheet has Duration specified at 0.35mm (.014") and 1.25mm (.049")
You guessed it first. I had not read your reply. Thought of it all of a sudden this morning.

[Dairymilkbatman]

I got
IVO @ 4° ATDC
and
IVC @ 38° ABDC
So with a duration of 222 I am getting there, right?

Are we concentrating on the duration because of my incompetence with measuring and reading a cam card? lol
You guys were right, I wasn't including the lash.
I am so grateful for the help. In the UK, there is little to no engine building - at least not like the US. Finding information here or someone who know's is hard.

So where do I go from here? once I reach 226 of course.

[modok]

176+38=214
not 222
Perhaps you added 4 instead of subtracting it.
Getting closer tho!

Don't sweat it, this IS tricky. I can make it sound simple but,
that's just because I"m naturally good at it, AND lots of practice

[MadBill]

Your reported numbers show IVO to be 7° late vs. spec and IVC 5° early, so only a 2° difference. Thus 'by the numbers', the cam is now only 1° retarded, so I'd say congratulations, you are done*! . (*Can be debated, but 1° is close enough for me.)

It would only be a check of the cam machining, but for peace of mind you could back off the checking lift point (say 0.008"/0.20 mm for a start), to bring the measured duration closer to spec., thus allowing direct confirmation. Ditto for the ICL.

[Nut124]

I got
IVO @ 4° ATDC
and
IVC @ 38° ABDC
So with a duration of 222 I am getting there, right?

Are we concentrating on the duration because of my incompetence with measuring and reading a cam card? lol
You guys were right, I wasn't including the lash.
I am so grateful for the help. In the UK, there is little to no engine building - at least not like the US. Finding information here or someone who know's is hard.

So where do I go from here? once I reach 226 of course.

If your numbers above are correct, your duration at the measured lift is 38+180-4 = 214.

More importantly, your lobe center is 4 + (214/2) = 111 ATDC, which is close to the spec 110. Race engines tend to use more like 105/105 at least in Fiat twincams for more overlap. Street is often 110/110 like yours.

Exhaust cam center, BTDC is calculated as follows: ((EVO+180+EVC)/2) - EVC. This is assuming that EVC is a ATDC value, not BTDC. If BTDC, then use a negative number for the EVC.

Do the same for exhaust to check lobe center as shown above.

Below is my cam timing chart with 107 centers. You could put your lift points on top of my chart and compare. The intake is a 294 deg advertised, the exhaust is 300deg but has a lot shorter actual duration because lobe profile is less aggressive and more valve clearance.

[Nut124]

I have a query, based on a hunch on the degree wheel. If - for example - the degree wheel was not centred on the crank nose, but offset. Do you think there is a possibility that it would consistently observe correct TDC and show correct numbers on and around that area of the wheel BUT, on the opposite side show incorrect numbers? Like a rotating mass would if it was out-of-round. I had to drill and expand the mounting hole to fit my crank nose, then I made a rudimentary centre washer to centralize the wheel on the nose. (No lathe) I'm wondering if I've cocked it up.

How far off center is the wheel. If it were 2mm off center, then the biggest error could be 2mm at the edge of the wheel when at 90 deg to the direction of the shift.

In my wheel, 2mm would be around 1 degree off at max. You could estimate your max error this way. Bigger wheels are less sensitive to off center error.

[Dairymilkbatman]

176+38=214
not 222
Perhaps you added 4 instead of subtracting it.
Getting closer tho!

Don't sweat it, this IS tricky. I can make it sound simple but,
that's just because I"m naturally good at it, AND lots of practice

Oh I see, am I right in saying I would use subtraction if the IVO ATDC? and addition if the event is BTDC?