Help with timing camshafts

[Dauner]

Rebuild of 1989 911 3.2. I am struggling with camshaft timing. I successfully timed the original camshafts several years ago when I replaced my timing chains.

This time I am trying to time my camshafts that were remachined by Dougherty to a DC-15 sport grind to go with my 3.2 to 3.4 upgrade.

My specific challenge is no matter what I do, I cant seem to float the camshaft into the middle of slop associated with pin fit. I either get out of spec on the low side or just barely in on the high side of the 1.7-1.9mm tolerance. I remember from last time that the forum recommended low end of tolerance for low end torque associated with a daily driver as opposed to race setup.

One challenge that I dont remember from last time is the sprockets just dont seem to want to coast on the end of the camshafts. I have polished id of sprockets mirror smooth with 2000 grit. Camshafts are a different story. I got them back from EBS racing and it seems like Dougherty put a rough chamfer on the ends which created a slight burr that I have tried to remove. Fearing doing irreversible damage, I've been careful about taking lots of material off before I know what's going on.

Is there a chance I did not receive my original camshafts back? If that were the case, could be a source of the problem.

I am in a process of trying to rotate the cam with my thumbs but inexact would be an understatement.

Do I need to disassemble everything and lick down the camshafts until sprocket spins loose and freely, or is there an alternative?

I fear it will take me 10X as long as last time, and I may not get left right the same.

Important note is I am still in valve piston clearance phase so maybe I'm putting too much time into timing camshafts for this part of the process. Will be disassembling everything again anyway. As weekend time is rare and precious, my plan until I get more feedback is to adjust cams to high side of tolerance (worst case scenario), check valve piston clearance, then worry about the sprocket/cam interference after full dissassembly.

Thoughts appreciated. Thx

Mark

[Flat6pac]

Watch Stompski racing info for timing cams. He sets the number then sets the torque.
By 993 the torque on the bolt is the only thing holding everything together.
Bruce

[Dauner]

Hi Bruce, my problem is cant get the proper number, with or without bolt being torqued down. Valve spring force is pushing on cam. No way to "hold" cam in place relative to sprocket on the newer style camshafts. I will watch the video.

[Dauner]

In the video he states "the camshaft will stay in place" when he rotates the engine. Mine does not. If I'm in position where the cam rocker are opening the valve, as soon as I pull the pin, the camshaft jumps a bit. Only way to avoid this is to do things with valve fully closed on compression stroke, but then you dont know where you are. I didnt have the problem with original cams. Not sure what's different this time.

[Flat6pac]

Put all the rockers in
Bruce

[Walt Fricke]

Right - with all the rockers in, there are counterbalancing forces at work.

However, these bolt end cams are a PITN to time compared with the big nut kind. I'm going to purchase the adjustable timing gears for the next time I do this with this kind of cam.

However, there is a nifty trick you can use to get the "slop" more centered on where you want it. Try skipping a tooth on the chain (at the IS shaft?), and find the hole where the pin will insert again. Ultimately you can get to where you want to be - you can even get your preferred lift to be at the fully tensioned pin position. If you use the search function, you can see where someone explained all this - which way to skip, how much, why it works, how many different timing position options there are, etc.

I'd start by just trying this or that.

Once you get to where the pin is in a suitable place, some say they can lightly tighten the nut, and then use a small screw driver to press against the teeth behind the gear with its holes to nudge things to where you want. Then full torque, recheck, etc.

[Dauner]

Thanks Walt and Bruce,

Excellent tips and advice. For the record, yep, when I replaced my timing chains last time all the rockers were in and adjusted. I'm confident that's what the difference is. I just didn't think of that. I'll search for the thread associated with skipping a tooth.

I'll be checking valve piston clearance over the holiday weekend. Fingers crossed, after that i can begin teardown and final assembly with sealants.

Mark

[Gordo2]

I've installed DC cams in my engine.

When John sent them to me, he had coated them with some sort of hardening material that made them look uniformly flat black.

I found this material coating made it very difficult to get the sprockets on the ends of the cams, and once on there was no spinning them to adjust timing.

John recommended I lightly polish the ends until I was satisfied with the installation and movement / rotation. I was hesitant and ended up incrementally polishing until I could spin / coast the sprockets on the cams without much resistance.

The description is midway down this thread: Difficulty Installing Camshaft Woodruff Key and Sprockets - 3.2L

My cam timing method is described midway down this thread: Gordo's 3.2L Engine Rebuild - Ready to Reassemble

Good luck - I clearly recall cam timing as one of the more challenging steps of my rebuild.

Gordo

[Trakrat]

Originally Posted by Dauner

Rebuild of 1989 911 3.2.

This time I am trying to time my camshafts that were remachined by Dougherty to a DC-15 sport grind to go with my 3.2 to 3.4 upgrade.


Mark

Just curious... why did you decide on the DC-15 sport grind?

I am also upgrading my 3.2 to 3.4, but was always suggested to me to go with 964 cams.

[Dauner]

Trakrat, sorry for the delay in responding...

Good or Bad, I didn't put a tremendous amount of research in to my cam choice. EBS racing helped with my selection to bore my 3.2 cylinders to 3.4 and replate with Nikasil, JE 9.5/1 pistons, and knowing I was looking for a daily driver, they said they have been putting DC-15 cams in engines for customers with my goals.

Mark

[Neil Harvey]

Originally Posted by Dauner

Trakrat, sorry for the delay in responding...

Good or Bad, I didn't put a tremendous amount of research in to my cam choice. EBS racing helped with my selection to bore my 3.2 cylinders to 3.4 and replate with Nikasil, JE 9.5/1 pistons, and knowing I was looking for a daily driver, they said they have been putting DC-15 cams in engines for customers with my goals.

Mark

Mark and to all others,

Never put any credence in a result with a parts house over an experienced engine company. That been said, here is my advice.

First off, if you did not check the RA finish on your cylinders before assembly, maybe re start your engine project by looking at the finish of the Nikasil plating. This may be another issue could have but after you get the engine running. I recently had a customer ship me cylinders replated by your supplier and had to have them redone so they would not destroy the rings.

Camshaft issue. If this is about trying to hit the number on the head by removing the play in between the pin and the gear, aim for an earlier number by rotating the crank "just" before your TDC mark, find a hole for the pin, then rotate the crank to remove the play in the pin. If you go past TDC, then go back and give a bigger amount before TDC. keep doing this until you hit the mark. If you are real close, nip up the nut or bolt and do your piston/valve clearance check.

If the crank strokes were checked, the rod lengths are the same, the piston comp heights and head heights are all the same, hoping the cam lifts are the same, you only need to check 1 piston.

Another way to check your piston clearances is noted on our wed site. Also Jeff, "home built by Jeff" has a video about how we do this. It will require you to ask for the valve lifts from 20 degrees BTDC through to 20 degrees ATDC. This way it removes any cam setting issues you are having to get clearance numbers, but you will still need to revisit the same issue when doing your cam timing.

Performing the cam timing at full lift (valve open) kinda holds the cam in place and allows you turn the cam gear to find the hole you need. We time the cams always at full lift as this way the LC's are split the same either side and removes any differences in ramps and radius rocker faces.

Have patience here knowing you will get it.

[Dauner]

Hi Neil,

Got the cams timed just fine and my piston to valve clearance met the general guideline of 1.5mm Intake and 2.0mm Exhaust minimum on #1 and #4.

What would be the cylinder wall Ra or RMS spec for my application? I am now in the process of tearing things back down to block to re-assemble with sealants so no lost time or effort on my part to take measurements.

Thanks,

Mark

[Neil Harvey]

Originally Posted by Dauner

Hi Neil,

Got the cams timed just fine and my piston to valve clearance met the general guideline of 1.5mm Intake and 2.0mm Exhaust minimum on #1 and #4.

What would be the cylinder wall Ra or RMS spec for my application? I am now in the process of tearing things back down to block to re-assemble with sealants so no lost time or effort on my part to take measurements.

Thanks,

Mark

It appears that your cylinder repair supplier acts as a 1/3 party without any sort of responsibility. The actual company doing the repair work do excellent work but they work to specifications. They need to know the acceptable ovality and taper along with the required RMS finish.

We use them often and always supply a written PO with finished specifications. We have never had any issues. From speaking to them (re plater) in our last go round, they were not given any spec's from the 1/3 party so provided my customer with what the 1/3 party has always accepted.

When the 1/3 party was asked why the cylinders came with such a high RA number, ( 26+) they said, we have a standing spec with the plating company.

But here is the rub, the re plater has very little room to lower the finish and still hold the required bore size. So its very important to give the re plater the finished bore size along with the finished Ra number at the beginning.

Nikasil does not need a high cross hatch to retain oil. You do not need a lot of oil up there. Nikasil is very hard and a high Ra number along with severe cross hatch with wear out your rings in a heart beat. The idea of breaking in a engine is to allow parts to bed into one another. Rings are often of a very hard surface like chrome which is hard to withstand this assault when rubbed up against the bore material. The bore material was softer, often cast iron. The rings wear down the high spots of the cross hatch and the rings bed in. The rings do not take a hammering as they are a hard surface.

Not to mention the frictional losses you will experience. The highest friction losses an engine has to over come is from the rings.

But with Nikasil, you cannot use hard ring faces. You cannot run two hard surfaces against one another , so no chrome. With Nikasil been so hard, the ring faces been softer, any high spots from high cross hatched finish just wears out your rings and smoke happens. Nikasil also allows the cross hatch angle to be different from a cast block as the lower finish number and lower oil content retained needs to spread itself over the same area.

A long winded answer to what you need. My guess is, if you had your cylinders supplied by this same 1/3 party, your finished surfaces are too high a number. Have them first checked to see what you have. This gets into touching areas for me as these sorts of details are kept very confidential. This is what our IP is.

I am happy to help and offer this service in the future to anyone who will then gain our knowledge and experience in asking the re plater to repair cylinders to our spec's.

In your case, if unsure, send them to us and we will measure and tell you what you have at no charge. Then if they need re honing, we can ship them to the re plater and have them re done to our spec's. You pay the shipping and the re do costs.