Valve timing

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Model T Ford Forum: Forum 2017: Valve timing
Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthony Bennett on Sunday, April 09, 2017 - 08:48 am:

G'day blokes,

My wedding is coming up, the old truck is in pieces and I'm trying to throw an engine together. What was going to be a simple swap of complete power plants has become a little more involved... the donor came to us as part of an unfinished project, by an unknown builder who I'm pretty sure was of unknown skill?

Seems the short engine was lavished with new pistons, fresh whitemetal and a reground cam, lovely, but sadly the cam gears were clashing, the thrust is ground off the cam, the clutch fork arm was loose, the trans cover had a broken corner and the trans itself was shot... Dad and I were both glad we had a closer look at this gift horse.

Luckily there's a few bits lying around that I've prepared earlier. I've already trued up a flywheel, balanced and recharged the magnets, had the magnet keepers ground once the flywheel was assembled. Fitted that lot to the engine & set the magneto clearance. The trans shaft is spot on, the drums are balanced and after much fettling, the clutch/brake/driven plate assembly is pretty straight as well.

What I found tonight was interesting though. Seems the engine machinist, (who I assume is much more qualified that the numpty who put the other gear on the outside) has fitted much bigger than standard lifters. I didn't measure them with a caliper but they appear some .050" bigger in the shank. They're not adjustable, but the clearances to the new valves are pretty uniform at around .025" - .026"

Knowing that reground cams, (with extra duration) can be a liability as much as anything, I've done a few measurements to try and verify the grind...

The method involved measuring the flywheel circumference at 1168mm and thus establishing 3.2mm x 365 is a poor mans degree wheel.

Seat to seat figures are something like this... provided I have my measurements right.

IN Open @ 14deg ATDC
IN Close @ 57deg ABDC
Duration 223deg

Exhaust figures...

EX Open @ 41deg BBDC
EX Close @ -9deg BTDC
Duration 230deg


Sadly my engine software went to the ether with a hard drive failure recently, so I don't have the ability to scrutinise the numbers very well, or make any changes to get a feel for what this thing will do. The cam is a bit low on lift, .245" on exhaust and .240" the intake but that's ok I think... I'm pleased enough that the duration isn't too long, according to the Tulsa Club tech advice ( http://mtfctulsa.com/Cams/intake_duration.htm )

So without trimming new valves to length, I'm stuck for time with the current lifter & cam combination, however I'm interested to know if anyone here has ideas on wether there's improvements to be made? I've heard some noise about a 7 1/2 degree cam gear, but I understand that helps more with a heavy car?

Mine certainly isn't heavy but it'll be transformed compared to the old engine I'm sure... the iron pistons and the complete lack of ring tension made it pretty unremarkable climbing any incline.

Cheers for your attention anyway.

Anthony


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthony Bennett on Tuesday, April 11, 2017 - 05:07 pm:

bump?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach, CA on Tuesday, April 11, 2017 - 06:09 pm:

Use a feeler gauge and set them at .010 on the intake and .012 on the exhaust. If the cam has been replaced you don't have to use piston position. If you don't have adjustable valve lifters you will have to stem heighten and now after rereading I see they are solid lifter so you will have to stem heighten. If they are set too lose you will have to grind the seats down to get a better setting. If they are too tight you will have to shorten the stem.

The reason for piston position was that not all lobes were correct on original engines so they used it to get a good average. Also farmers didn't have a set of feeler gauges but they did have a ruler so could measure piston depth and find where to do the grinding. You have a replaced cam and so can set them with a feeler gauge.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach, CA on Tuesday, April 11, 2017 - 06:11 pm:

And two more things, they will make a lot of noise at .025 and you will lose horsepower.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthony Bennett on Thursday, April 13, 2017 - 07:32 am:

Thanks very much Frank,

I suspect the clearance will be noisy, but it also limits the duration a bit, which seems to be important according to the info I can gather.

I'm wondering if the intake closing or intake opening is the most important factor in developing low down torque...

You mention "stem heighten" which is a new terminology to me, what does that require? I have wondered wether I can get some lash caps to close up the exhaust tolerance, even if I have to trim the valves to adjust.

Cheers

Anthony


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthony Bennett on Friday, April 21, 2017 - 09:00 am:

Well I bought the software and did the modelling.

Standard cam timing is actually a bit retarded so I assume that's why the 7 1/2 degree cam gears are proving to be an interesting accessory for many.

My reground stick was the best part of 10 degrees retarded! Lift was a little low at .240"in & .245"ex but at least that means the duration wasn't too excessive.

The upshot is I've fitted the new cam gear a full tooth forward, roughly 4 degrees advance along with a Zed head should make it pull pretty well, even though I'm a little further forward that the recommended "best average torque" position.

According to the technology, "optimum" cam advance for outright peak torque was 18 degrees(!)advance but the loss of power at 2000rpm was significant. Conversely the optimised position for peak horsepower was 4 degrees retarded.

It'll be interesting to see how it goes...

Cheers


Top of pagePrevious messageNext messageBottom of page Link to this message  By Glen Chaffin on Friday, April 21, 2017 - 11:59 am:

Anthony, Advancing the cam gear 1 tooth will advance valve timing 15 degrees, not 4 degrees. your cam should be advance about 12 degrees, not 15. 15 degrees is too much. Glen


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