Camshafts...

[jason_]

Hey forum, been registered, and decided I ask a question, as I can't find any info.....

I don't own a festiva, but an aspire. Not sure if the same 1.3 was carried over. Anyways I do mad machining myself, and I want to further, but I'm stuck..

My last rebuild I milled 0.038 off the head to bump the CR, reason was waiting 4 days for pistons and decided to experiment. Turned out beautiful. Only concern was the tensioner pulley almost wouldn't take up the slack, it worked, but could of been tighter.

Now I think I shaved enough to get between a tooth, hence I think my cam is a fuzz retarded, or crank is a fuzz advanced... One of the shafts must walk the belt as the head drops......

Who's got an idea to compensate? The only way to avoid it is to mill enough for the gear to walk one full tooth, so I can avoid "not enough or too much"...... Buuuutt, milling that much might bump my CR too much, unless someone knows CC chamber sizes.... I went totally blind on the first mill....

I'd gamble 0.07, or even 0.1, but if I still don't jump a full tooth, I'm needed to have an adjustable cam gear. And on top of that idler pulley idea. I thought about building up the factory one with weld and turning it down in the lathe so it's a fuzz fatter in diameter.

Ideas?

[zoom zoom]

Welcome to the dark side...don't let these guys talk you into being a suspension swap!

I asked arty last night, he may chime in, but b6 and bp adjustable cam gears for miatas will work on a b3 cam.

[Bert]

Welcome to the dark side...don't let these guys talk you into being a suspension swap!

We would never do that...at least not while it's still moving. But Jason could start by pilfering Rio front brakes and top hats so that when the time comes his car is more desirable to a Festy owner.

[jason_]

Re: Camshafts...

Haha, glad someone is able to help. Seems there's always someone pushing the envelope, and one is me for sure.

Part# or a link?

Any other ideas what to do for the tensioner to pull the timing belt slop?

[blkfordsedan]

If the B3 sprockets are the same as a B6...
The belt is 8mm pitch and the cam sprocket has 46 teeth, giving it a pitch circumference of 368mm. You milled the head .038" or approx .965mm. If you do the math, every tooth on the cam sprocket is 7.82 degrees, which means the actual valve events would change by 15.64 degrees. Also, every 1.02mm worth of displacement rotation at the pitch diameter of the cam sprocket is 1 degree of cam rotation. You milled the head .965mm, so you displaced the cam by .986 degrees, which in turn retarded the cam timing (I.e. valve events) by 1.97 degrees.

As you can see, your not even close to being able compensate by moving the sprocket a full tooth. Truthfully, retarding the cam timing by just under 2 degrees won't make much difference. You may notice a slight decrease in low RPM at the most. The easiest way would be an adjustable cam sprocket. If you advance the cam sprocket between 1/4 and 1/2 tooth, that would be about 6 degrees of crank timing, which would net you about 4 degrees advanced with milled head.

I have pondered using my degree wheel to zero in on the cam timing I want (about 4 degrees advanced) and drilling a hole in the end of the cam and sprocket. I could then drive a roll pin through it to lock it into place. If I decide to do this, I'll post it in my garage thread.

The tensioner is a bearing, so I wouldn't weld on it. I would probably try to press a hardened steel sleeve over the outside to increase the O.D..

[georgeb]

How about if you filed the adjustment slot a little bigger in the idler? Don't know how to fix the retard prob. My old Nissan had several different ways to install the cam gear to adjust the timing of it.

[blkfordsedan]

The adjustable cam gear is really the best option if you have the money. The ability to make cam timing adjustments quick and easy and be able to play around with it would be very beneficial. If you went from 2 deg retarded to 4 degrees advanced, I bet you would certainly notice the difference in the normal driving range.

I know the adjustable cam sprocket for a B6D Miata will fit a later model B3, but I'm not sure about the early B3. My early B6 has a round tooth HTD style belt....and I think the later B3/6 and B6D had a square tooth belt.

[FestYboy]

all B series sprockets use a round tooth, SO, any Miata cam gear will work with our engines.

[Safety Guy]

Here's Corksport's adjustable timing gears:

http://www.corksport.com/corksport-b-series-dohc-camshaft-gear-set.html

Here is another one, OBX, which seems cheaper, but they distinguish between Protege and Miata:

http://www.rsaperformance.com/obxmacamsp.html?utm_source=googleshopping&utm_medium=cse&gclid=CKnXmpnnprMCFUWo4Aodnh4A7w

Need to know for sure before ordering!

If this is the best price we can find I'll go "halve-sies" on these. I can buy both and then you can send me half payment for the spare sprocket and your share of shipping.

PM me if interested.

Karl

[Safety Guy]

Here's another link, OBX for both sizes of Miata (B6 and BP):

http://www.rsaperformance.com/obxcamgemami.html?utm_source=googleshopping&utm_medium=cse

$139 from RSA. Should be the right pair.

Karl

[zoom zoom]

Man those corksport gears are nice..

[jason_]

Re: Camshafts...

Didnt forget about this, got my 383 stroker sbc going, so busy hauling firewood for the next few days, ill keep get to this this weekend. Appreciate the help.

[blkfordsedan]

all B series sprockets use a round tooth, SO, any Miata cam gear will work with our engines.

Best news I've heard all day. Rock auto lists the B3 timing belt as a square tooth...which made me nervous. No reason to screw around trying to redrill drive pin holes and stuff, I'm just putting my cam in "straight up" for now. I'll buy an adjustable pulley next spring if I want to
mess with the cam timing. Well see how (or IF) it runs first.

[jason_]

Re: Camshafts...

This is on hold until I get a problem figured out...

[jason_]

Re: Camshafts...

How wild can a man get with cam advance with stock grind? Disregarding emissions of course. Since this is going to be at least 10.5:1, ill have to get out of the habit grabbing 5th @ 25mph for downtown cruising. Maybe it won't be too bad without tps calling for ignition advance

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