OT porsche content Anyone ever use a degree wheel?, DOHC 1 cam is good the other... not so good Options

[rick 918-S]

I am nearing completion of my rebuild. I have the long block done but I have an issue with my cams. Because my heads are now shaved 1mm my right cam is not on the mark. Here's a couple pics of how things are. After one full rotation the right cam appears to line up with the mark when the crank passes TDC 5 deg.
I have off set keys I can install, but because I have two cams do I need to use a 2.5 deg key or a 5 deg key? or what? (IMG:style_emoticons/default/confused24.gif)

[byndbad914]

Rick, it seems odd to me that one cam would be spot on and the other off. If both heads moved closer, I would expect an issue at both cams and depending on where the tensioner is placed (btw, I don't see a pic of the setup) would dictate whether they both move in the same direction, or one adv one ret.

I wouldn't look at the keys for degreeing a cam. I have used a degree wheel a number of times and here is where this may fall apart - you will need the degrees of crank rotation for intake and exhaust valve events. English = you need to know at what degree on the wheel the intake valve opens to 0.050" lift (or maybe some metric lift value since it is Porsche), is closing at that lift and the same for the exhaust. Otherwise there is no reason to attempt to degree a cam.

If you are just trying to line up the keys to a reference mark at TDC, you won't need a degree wheel.

So, assuming at TDC one cam is spot on and the other is lagging 5 degrees on the balancer, I suspect you need 2.5deg on the cam. The reason is not two cams, but because they turn at half the speed of the crank. So if your crank spins an extra 5 degrees to get the other cam at "zero", I would guess it needs to go forward 2.5deg.

If you have valve events and want to discuss cam degreeing, let me know and I can PM my phone number. Easy to talk than type for me (IMG:style_emoticons/default/biggrin.gif)

edit - I see the pics now for some reason not before

[rick 918-S]

Ok, That confirms my other sources.

Next issue, I still think somethings not quite right. When rotating the crank everything is smooth until 180 deg. then I can feel a slight resistence. TDC rotates through the cycle fine, but come around to 180 at TDC and there is a slight resistance. I think I'm contacting a valve. I need to figure which one. Maybe the exhaust on #1. That was the one that broke last time. I may be on to something here.... (IMG:style_emoticons/default/idea.gif)

[911quest]

One thing you can do (fabricating involved) is what I used to do on watercolled VW, when I would run into the same problem use an adjustable cam gear to dial the cam in. We used to make them cause we where to cheap to buy them one other thought...is the cam gear keyed or is it tappered?

[jd74914]

911guest might be on to something if you want to go that route. I just finished reading a book (as I am looking into advancing the timing on a CBR600RR engine) that talked about making the cam gear adjustable by setting a dowel into the cam and the drilling holes in the cam gear for that dowel to fit into with one at the right advance/retard.

Its a pretty simple procedure, but if you can just use an off-the-shelf key to get that same result that's probably better.

[rick 918-S]

I'm using a Mercedes Key. I had to grind the half moon flat but it fits the slot width fine.

I'm having a friend (mechanic) stop over tomorrow. I'm freaking myself out over this silly cam thing. I don't know why, I used to drag race and built lots of BBC's But tonight I just walk away from it. This thing is costing me big. I'm afraid to start it now. I checked everything 4 times so I'm sure everything is good to go but... just needed to vent a little here.

[byndbad914]

I'm using a Mercedes Key. I had to grind the half moon flat but it fits the slot width fine.

I'm having a friend (mechanic) stop over tomorrow. I'm freaking myself out over this silly cam thing. I don't know why, I used to drag race and built lots of BBC's But tonight I just walk away from it. This thing is costing me big. I'm afraid to start it now. I checked everything 4 times so I'm sure everything is good to go but... just needed to vent a little here.

Rick - a lot of guys, even mechanics, don't really know how to check piston to valve clearance. I do, and if your problem is right at TDC, it most likely wouldn't be #1 hitting but the companion cylinder (the one at overlap). Additionally, it won't be right at TDC, it will be just before when it is chasing the intake or just after as the exh valve chases the piston.

Companion cylinder = at TDC at same time. So, for firing order, split in half and lay above each other, the ones that line up.

So, say firing order on a SBC 18436572

1823
6572

companions are 1 and 6, 8 and 5, etc. So when 1 is TDC, #6 is TDC during the overlap events. #6 is where the valve to piston clearance is an issue. Just write out your firing order and do same thing - the one under #1 is where you want to measure if you are around TDC FIRING of #1. When you are "180 out", you are trying to fire #6 when both valves are open.

If you really want to be sure, either get what is known as a checker spring (a simple spring that is easy to depress by hand and htere just to hold the valve up) and a dial indicator. Put the checker spring on #1 intake - or if the valve stem seal will hold the valve up, just forget the spring - and get to about 120 degrees (so you are coming up on "180 degrees out"). You should have the rocker on to follow the cam and a dial indicator on the retainer or right above the valve stem on the rocker arm will do.

Now, with your degree wheel on, check the piston to valve on the intake by pushing the valve down 'til it hits the piston and look at the indicator. Should be a bunch, if it even touches the piston at all. Go 10 degrees, should be less, go another 10 and check.

You should find that the tightest clearance is not TDC but before it. Go back to that 10 degree increment and go 1 deg at a time and measure until you find the tightest value. YOu need at least .080" to be safe on the intake - the alumimum heads buy you a little extra too so you could be tighter, maybe down to 065" but I wouldn't recommend that. Now, at TDC (180) or just after, the exh valve should start to open. Measure clearance at TDC on the exh, go 10 degrees, measure again blah blah until it starts increasing again. Go to where the tightest and move thru that 10 deg increment 1deg at a time and find the tightest amount. You want a minimum of 0.100" on the exhaust. I would prefer to see you have 080 int and 120 exh. If you are less than that you will probably bend a valve. If you are half those values, you will bend a valve for sure.

Best of luck - be safe, not sorry, it is much better to be gun shy than drunk and waving the thing around (IMG:style_emoticons/default/laugh.gif) That takes a long time to type but an hour at the most in practice if you have a spring remover that you can use with the head on the motor. If you need to verify what I mean, just PM me and I will shoot you my number. I check this during the day when work doesn't get in the way of my pleasure (IMG:style_emoticons/default/dry.gif)

edit - it's late and I just proofread AFTER posting. Big mistake. I got the valve events backwards and that is probably obvious. The piston chases the EXH at overlap (pushing out hte gases) and the INT chases the piston (to suck in the charge). So check exh on the way up and int on the way down. The method is the same of course.

[rick 918-S]

Thanks, That's alot to type. The problem is at or just before 180 deg. which would put the event at #1 The valve checking method you discribe would work fine for a chevy however, this is an overhead cam engine. It's hard to get to the valve springs with the valve cover on. The valve cover is actually the cam housing. the lobes push on a big hydrolic lifter sitting directly over the valve. This is also an interference engine so if both cams are not cycling, both cams need to be removed to avoid damage.
1. The crank spun fine prior to the installation of the pistons.
2. the assembly spun fine prior to the installation of the heads and cams.
3. this should rule out a crank problem or the rotating assembly.
4. engine turns smoothly until the intake/exhaust valve event at or near 180 deg.
5. visual inspection doesn't reveal an issue.
6. I need to check for a damaged ramp on the cam. This could be damaged as a result of the failed valve. Maybe the cam is binding on the lifter as it tries to move the lifter.
I can see into the cylinder through the spark plug hole and intake/exhaust ports as the valves move through their cycle. I don't see any marking of the piston notches at this point. I'm sure if the valve was contacting the piston It would leave a light mark in the notch.

Thanks for the offer of assistance. I'm really thinking out loud here as I sort through this.

[911quest]

Rick I would try to retard the cam one tooth back wards just to see if the binding stops,

[rick 918-S]

Rick I would try to retard the cam one tooth back wards just to see if the binding stops,

Did it, The event moves inducating cam trouble with #1 intake and exhaust valves. Same cylinder that failed last time. I was thinking coil bind but this is at the start of the event not max lift. I'm pulling the euro cam on the right bank and installing a US spec one to see if I can confirm.

Thanks,

[andys]

Rick,

I suggest there's no easy way around this without some amount of work on your part in order to ensure everything clears properly. If you use the indicator and firing order method, make sure you know how Porsche numbers its cylinders (eg. Ford is different than Chevy). Glad to see you though about coil bind; it's often overlooked. Are all the springs the same? Valve stem installed heights the same on all?

I agree it's highly likely that the two cam dots *should* line up as long as you don't have some kind of weird mixture of parts. For example, do the Euro S cams used different cam sprockets than say the US versions?

I think I would just go old school at this point and simply clay every piston/valve in order to be absolutely sure where the problem *might* be. It'll take the guess work out of the whole thing. From there, you can focus on the problem if in fact there is one.

Good luck,

Andys

[rick 918-S]

US and euro have the same gears. I'll know if it's cam related soon. I don't want to pull the heads if I don't need to. I just torqued down $ 200.00 worth of special head gaskets. (IMG:style_emoticons/default/wacko.gif)

[911quest]

US and euro have the same gears. I'll know if it's cam related soon. I don't want to pull the heads if I don't need to. I just torqued down $ 200.00 worth of special head gaskets. (IMG:style_emoticons/default/wacko.gif)

I have never had a 928 apart is it possible to get the cams swaped side to side ( like a 911)?

[alpha434]

It looks like that, after head clearancing, your cams are a whole tooth off or something. The geometry gets weird.

The interference that you're feeling could be that a valve is only touching because the cam is out of position in relation to the crank.

EDIT: best option is to shim the cam gears around with a sacrificial gasket until you find the right combo to make everything right.

What kind of head gaskets do'ya got? Are they copper with the inlaid o-rings?
Just curious... 200 bucks in gaskets and all...

[rick 918-S]

Not on my engine. I never took the cams out of the housings and the left cam housing has the distributor drive housing bolted to the front.

I swapped on a US housing and cam before lunch. It have a different style gear. (early square tooth, I'm using late round tooth) The square tooth gear worked to run the cycle. It seemed like it was fine until about 3/4 revolution then I hit a tight spot. This could have been caused by the difference in the shape of the tooth binding on the belt now. So I'm heading out to change the gear and try it again.

I'm trying to rule out the new exhaust valve as the problem.

[rick 918-S]

I swapped cam gears to the round toothed style and rotated the engine. Everything was fine. I checked the lifters in the euro head. The exhaust lifter was real soft, (not pumped up like the intake) I swapped in a lifter from the US head, put Amzoil Red Lithium grease on all the lifters and the valve stem tops, re-installed the euro valve cover, rotated the engine through the cycle and everything was fine. I may have had a damaged lifter. Several cycles around without issue.

I'm not really surprised the lifter was sticking and damaged. The exhaust valve sheared off at the retainer that rides inside the lifter cap. When I was doing the tear down I discovered a bent rod also. Shoulda checked it before I assembled the valve cover. shame on me..

Getting closer. (IMG:style_emoticons/default/huh.gif)

[lotus_65]

sweet.

hey i have been reading your progress thread finally, and i didn't see the answer to the question about firewall clearance. is there any way to get that motor in there without all that surgery to the firewall? i see that you need access to the dipstick, and it looks like any alternator or belt issues would mean dropping the lump.

your running a 915 gearbox, right?

i know of a 928 available for $1500.00 (obo) ... and i'm thinking... (IMG:style_emoticons/default/idea.gif)

it's a '79 (k-jet, 219bhp), so would a 901 hold up?

[rick 918-S]

sweet.

hey i have been reading your progress thread finally, and i didn't see the answer to the question about firewall clearance. is there any way to get that motor in there without all that surgery to the firewall? i see that you need access to the dipstick, and it looks like any alternator or belt issues would mean dropping the lump.

your running a 915 gearbox, right?

i know of a 928 available for $1500.00 (obo) ... and i'm thinking... (IMG:style_emoticons/default/idea.gif)

it's a '79 (k-jet, 219bhp), so would a 901 hold up?

Hi Paul,

No, The length of the assembly dictates the placement. However there was a guy in Germany that built a 16 valve and a 32 valve 914 conversion. In the photos of his engine bay it appears his engine is further back than mine. I placed mine where it is because I wanted to retain the rear trunk.

$ 1500.00 for 219hp is alot. There are no HiPo bolt on parts unless you buy euro heads,spyder and intake setup. Used euro heads are a cool $ 1000.00.

I am using the 901 built by Brad Mayuer, HB gear, Billet intermediate plate. So far so good.

[Cap'n Krusty]

Excuse me for asking, but you say this is a DOHC engine,. The description of the problem and what you're doing to solve it, as well as the picture, indicate it's a SOHC engine. Big difference in the heads and cam towers, as well as the number of potential problems. The Cap'n

[lotus_65]

yep, thanks rick.
the price i saw was for the whole car in decent shape, so i thought about parting it out to recoup some investment. though i don't think there's much of a market for those parts, and storage is an issue at the moment.
there is value to me in a "known running" drivetrain verses a boneyard lump. also, there's a blank steel-flared chassis in the classifieds to mate it to and allow me to build it to my specs.
the idea was to get the architecture correct and shake it out well with something like this before stepping into a larger hp s-spec 8.
of course it's a complete pipe dream as i have failed to win the lottery as planned...(IMG:style_emoticons/default/biggrin.gif)