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short belt

9

90volvo

Active member
Joined
May 27, 2017
Location
Eldorado Springs Mo.
Have b230ft That i had the head milled a quite of bit. I had .070 taken off and running a .030 head gasket. The stock belt is to loose, it jumps a tooth when I try and dive it.

Ive done alot of searchiing and come up with T013 for a belt. So on the cam gear do i need to advance the cam or retard it? Any help will be appreciae it. thank you God bless pkm
 
Round tooth or square tooth setup?

Iirc, with that much off the head, running straight up on timing would put you at a good spot. The timing belt being shorter makes up for the change in cam timing
 
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So the square timing belt teeth are actually a Trapezoid. Gates taught me something. Should be a monster engine Kevin. Is that trans gonna handle the power?
 
got it

I also thought about taking a piece of pipe and pressing it onto the tensioner bearing but unsure if that would be enough. So with shorter belt will that retard timing or?

As far as trans, unsure. Been to track once, ran 13.90 at 114 mph. I came home pulled head and had it milled. Trans fluid already has clutch dust in it. Will keep you posted its a 4L60e has warranty. Funny trans guy was like 4 cylinder heck yeh we will warrany. I was like well I have turbo on it, he just laughed and said any troubles bring it back but we have that same trans behind 800 ph sbc.
 
90volvo said:
I also thought about taking a piece of pipe and pressing it onto the tensioner bearing but unsure if that would be enough. So with shorter belt will that retard timing or?
Click to expand...

With the head shaved and the shorter belt, timing will be pretty much unchanged.

What camshaft are you using? Setting the intake to a specific lift at TDC is a good and consistent way to set the cam timing.

You just need a dial indicator.
 
culberro said:
Round tooth or square tooth setup?

Iirc, with that much off the head, running straight up on timing would put you at a good spot. The timing belt being shorter makes up for the change in cam timing
Click to expand...
Huh? It's Friday after a long week and I'm confused. I didn't think the length of the belt had anything to do with the cam timing, as long as the tensioner can take up the slack and the tooth pitch on the belt remains the same.

The cam gear is spun around by the belt, which is pulling from the crank gear, around the aux gear, to the cam gear. The tensioner just takes up the slack _after_ the cam gear. No matter what length the belt is, the distance in teeth between the crank, around aux, to cam gear is the same since the crank gear is pulling through that path. What am I missing?

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For timing changes due to shaving the head, my back of the envelope math is:
- cam gear is 34 teeth, or ~10 cam degrees per tooth
- the gear and belt pitch is 0.375" per tooth
- shaving the head by 0.1" needs ~1/4 tooth of backwards cam gear rotation to take up the slack, which gives a change of ~2.5 cam degrees (counter clockwise / retard) per 0.1" of head/gasket reduction
- the tensioner needs to take up 2x the shaved distance, or a shorter belt is needed.
 
bobxyz said:
Huh? It's Friday after a long week and I'm confused. I didn't think the length of the belt had anything to do with the cam timing, as long as the tensioner can take up the slack and the tooth pitch on the belt remains the same.
Click to expand...

You're math is correct. I derp'd after a long week as well .. ain't no way someone is shaving off a full pitch :rofl:

But due to the general nature of my statement, ~2? at the cam (but 4 at the crank) isn't too much of a difference (see I'm trying to engineer logic my way out of being wrong)
And I stand by my statement that people should be measuring TDC lift :)
 
KL Racing sells 1-tooth shorter belts, I get parts from them in 2-3 weeks. I have a round tooth one I?m not using if you?re in a real bind. Time the cam properly with a degree wheel/indicator.
 
On old Fiat 8V L4's, typical performance mod of shaving the head (and cambox) results in cam timing being off at least 1/2 tooth advanced. Changing length of belt or larger OD tensioner bearing doesn't change that fact. On those, an adjustable gear is required to be able to retard the cam gear relative to cam to get original cam timing back.

Why would it be different in this case?

EDIT - never mind, you saying the shorter belt would allow the stock gear to align correctly with the factory markers, assuming the decking removed enough material to account for one tooth deviation.... seems likely an adjustable gear would still be required to confirm correct timing though...
 
bobxyz said:
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For timing changes due to shaving the head, my back of the envelope math is:
- cam gear is 34 teeth, or ~10 cam degrees per tooth
- the gear and belt pitch is 0.375" per tooth
- shaving the head by 0.1" needs ~1/4 tooth of backwards cam gear rotation to take up the slack, which gives a change of ~2.5 cam degrees (counter clockwise / retard) per 0.1" of head/gasket reduction
- the tensioner needs to take up 2x the shaved distance, or a shorter belt is needed.
Click to expand...

Reading this and thinking about it has made me revisit the math I've thought I had locked in for like a decade. As it turns out, I was wrong in stating that every 0.010" you mill retards the cam 1 degree.

The one thing you missed here is that yes, there are 38 teeth, but also 38 valleys, for a total of 76 "positions" on the gear. I just went out and measured one, it's 4.48" across the teeth, 4.31" across the valleys, let's call it 4.40" mean diameter. That makes the circumference 13.8226". When you divide that by 720 (the number of crank degrees in 1 combustion cycle, how a cam is measured), you get 0.01919, or about 0.020". So every 0.020" you mill the head, it retards the camshaft 1 degree.

My error that I've held on to and argued I had compared to results from a degree wheel (which I remember doing but I've gotta say, perhaps mistakes were made) is that the belt gets shorter on both sides of the cam gear, which it does. Let's say you trim 0.040" off the head, well in order for all the pulleys to stay in exactly the same place the belt would need to be 0.080" shorter, which is correct, but it would not require that the cam gear rotates anti-clockwise 0.080", retarding it 4 degrees, it rotates anti-clockwise 0.040", retarding it 2.

I really apologize for the goof and the number of times I made this argument. I'm also going to go back and look at the math on the cam gears we made to see where our cam timing actually was.

My brain hurts.

BIG EDIT

OK, I couldn't let this go. I chucked the K cam in the race car and measured it up. Volvo says that with 0.5mm valve clearance the intake valve should open at 22.6* BTDC. We found that in our application, it opened at 12* BTDC, or 10.6* retarded. The head is milled 0.109", and we use a 0.030" head gasket, which, to my knowledge, is 0.017" shorter than the factory gasket, compressed. THUS: 0.126" removed between head and block nets 10.6* retard, or 0.0118" per degree. Bear in mind our dial indicator is only accurate to 0.001", so there is a margin for error here, but in general, you cut 0.010", you retard 1*.

PHEW.
 
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But remember, crank degrees are double cam degrees.
So 0.010? off the head is a 1? change at the crank. Which is where everything should be referenced from.
 
Well i made the tensioner bearing bigger by pressing a piece of 1.72 ID pipe on it. I then tack welded in a few places, taking my time and not allowing heat to destroy the bearing. It seems to work great, but to get everything to line up I had to use my adjustable gear. Which I had to advance the cam.

I would like to set cam up with a degree wheel, I know how to do that. But I have no info on the ipd camshaft, I was disappointed to I didnt recieve a spec card. i have the wheel and need a dial indicator. Which is no biggy been wanting to pick one up anyways.
 
Did you not end up using a shorter belt, and just went with the larger diameter tensioner modification to take up the slack? How does the tension on the belt feel? Is the cam actually advanced, or is it straight up, and that is just what the cam gear shows it as being after adjusting the gear to synch with the belt teeth?
 
tbrcktch said:
Did you not end up using a shorter belt, and just went with the larger diameter tensioner modification to take up the slack? How does the tension on the belt feel? Is the cam actually advanced, or is it straight up, and that is just what the cam gear shows it as being after adjusting the gear to synch with the belt teeth?
Click to expand...

for now, Im running a stock size belt; but I took a piece of pipe and pressed it onto the bearing to make it larger in diameter. I then tack welded it in a few places. IT works greats, when I set up the timing. I had to advance the came a few degrees to get it setup correctly. I had a stock gear on it but it would not line up right. So I had an adjustable ipd and I used it, Im guessing I could of went the other way and retarded I think. Car is up and running and runs good just have to do some tuning. I would like to degree camshaft in but have no specs on the IPD turbo camshaft.
 
90volvo said:
I would like to degree camshaft in but have no specs on the IPD turbo camshaft.
Click to expand...

The IPD Turbo cam is basically a ENEM V15T
Time it so TDC intake lift is at 1mm. (bolded section below is the intake TDC lift)

Volvo B21/23 V15 Turbo: 256/112/11.9/1.0
 
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