HELP! Timing Question

[82targa]

I hate sounding like a novice, but I believe that when you don't understand something you should ask. So here goes..... I got these specs from Web Cams for the 20/21 grind. How do I set this up. I can use the dial gauge but have absolutely no idea where to set these numbers...... Help
~Damian

[Tim Walsh]

82,
From the looks of it you set the crankshaft to TDC and set the intake to 1.9 to 2.2 (lift) on the dial guage. IE use wayne's procedure in his rebuild book but use 1.9-2.2 as your measurement with 0.10 valve lash.

[aigel]

The problem is that you are confused by all the cam specs on the sheet. While all those numbers are important to have when you plan an engine, it shouldn't be called valve timing sheet, rather than cam spec sheet, IMHO. As Tim pointed out, the 1.9-2.2mm number is what you will have to adjust cam timing to. How to proceed should be in your manual.

George

[82targa]

Thanks guys, I timed the motor using the the rebuild manual and the specs in that manual. the engine performed poorly. The only problems or questions about the rebuild was the O2 sensor and the timing. I am getting the sensor put in the headers today and dropping the engine this weekend to do the "final" torquing on the cylinder head bolts and will care of this timing issue.

~ Damian

[Wayne 962]

Set your overlap to 2.1 or so, and you should be fine...

Is this clear to you, or still fuzzy?

-Wayne

[82targa]

I took the engine down today to re adjust the timing and do the final torquing. Bad news...... zero compression on left bank....careful examination through the spark plug holes reveals that valves have been hitting pistons... could this be because of weak springs or overlap of 1.1 instead of 2.1

~Damian

[82targa]

I will tear down the top end this week to confirm

[Wayne 962]

Could be - I would guess that simply setting the timing back to the proper value may fix everything. I doubt that you bent valves...

-Wayne

[82targa]

Wayne,

I tried pressuring the cylinders using compressed air, all leaking through exhaust valves.....

[PorscheTSC]

Hello 82 Targa, My advice is not a lot and a bit late but here it is all the same. When I find myself in a situation where Im not certain ,rather than risk it I grab so real time help. Such measurments as those you inquire about are critical so if your not certain find the best local machine shop and hand this task over to them. To your machinist setting these tolerances is a small task and one for which they should not charge a lot for. I would handle all the assembly myself but then glady let the shop set the cam timing just to be safe.

Best of luck ,The most important thing is not to let frustration get the best of you . When I was 16 (long time ago) my first car was a 1969 GTO . I built a 400 for in the car and all was well. Then the car's alternator failed so I decided to put a new one on ,no big job, unless it gets dark on ya like it did on me. Well it seems when the sun set my vision went low and I hooked the damm thing up backwards. The statement "let their be light " certainly held true that night. I fried the wiring from the firewall out . Frustration got the better of me and I grabbed a hammer from the toolbox and reformed the entire drivers side valve cover.This of course did nothing more than give me two jobs the next day ,rewire the car ,replace the valve cover . Hang in there ,be patient and you'll get it .

Randy
1970 911T
1998 Caddy Catera
2002 Ford E250 cargo van

[Wayne 962]

Originally posted by 82targa
Wayne,

I tried pressuring the cylinders using compressed air, all leaking through exhaust valves.....

This will happen if your timing is all screwed up. Check / adjust the timing, then re-run the test...

-Wayne

[82targa]

I remove the cylinder heads today. Here are some pictures of what I found





Definitely valves to piston contact. Someone mentioned that tensioner failure can cause this. I am using the solid tensioner:



could there be a problem with this. I replaced the hydraulic tensioners with these....Was this a good move?

~ Damian

[PorscheTSC]

Hi Damian, Again I am far from a Porsche Pro so hopefully some of the Pros on this site will return with some sound advice. I would not see where replacing the hydraulic tensioners with solid would have any bearing on this. The tensioners look good in the pics. When doing the engine build did you change out any of the original items such as Pistons , Rods or Crank. If you did change out any of these parts did you replace with original pieces or did you upgrade to more substantial pieces ( ie: longer rods,higher dome pistons,larger crank) ? If you did happen to upgrade ,did you spec out the new parts and allow for the proper Piston to Valve Clearences??

If none of the above applies and you simply rebuilt the engine as original then it must have been the cam timing setup. If you find this was the problem then do as I would do . Once you are ready to re-assemble the engine,load it up and head for a reputable machine shop. Those guys are pros who make their livings building motors. If all they have to do for you is set the cams /timing they should not charge much. This way you wont have to agonize over what might happen when you fire it up. It is worth a few bucks just for the piece of mind. Hang in there you'll get it .

Randy - PorscheTSC

[Doug Zielke]

You have changed the stock SC cams for the 20/21 Webcam grind, yes?

If so, you should have checked the piston to valve clearances, using solder or plasticine. Even considering the 20/21's relatively mild timing, clearances should still be checked. From your picture, the piston looks like it was contacted quite hard. I'd check the valves carefully to see if they are bent.

[cstreit]

It's very likely that your exhaust valves are bent. In the picture, the contact is on the exhaust side.

Since you just installed cams, it is most likely that you timed them incorrectly and caused this... THe good news is, the pistons are probably reusable and it's clear you didn't drop a valve which would be catostrophic...

THe bad news is that your exhaust valves and guides will need replacing most likely. Did you turn the motor over by hand when you installed the new cams? A failed tensioner COULD have caused this, but seems awfully coincidental... If you are going to use the mechanical tensioner, at a MINIMUM get the collars that prevent collapse...

[82targa]

Hi Guys,

Thanks for all the input.
Randy the only significant change to the engine was the 20/21 gring on the cam. They did not send me any specs on it so I assumed the standard overlap would be fine. We turned the motor over by hand several times and felt no resistance. what is very unusual though is the #5 and #6 cylinders are perfect!!. The motor ran a little "choppy" during the break in process but we thought it was the cam. During the first 500miles we would hear a metalic clinging noise on deceleration but, since we installed Dansk headers and two in two out muffler we thought it was normal. Being the novice we are we also left out the O2 sensor. "Like walking around the room with the lights turned off" -Wayne. Now we know.

Doug, I will check the clearance this time. and get the collar for the tensioner.

We will replace all valves and valve guides

[Wayne 962]

Every single camshaft has it's own timing value - there is no 'standard' timing spot.

You can check the timing with your dial gauge with the engine still in the car...

-Wayne

[82targa]

Now I am totally confused, shouldn't all SC grind carry the same overlap which would make it standard for that shaft/grind? (assuming that there is mimimal wear).

[Wayne 962]

Let me rephrase. Every single camshaft "grind" has it's own timing value. There were variations over the CIS cams, as there were variations between them and the 964 cams. All SC cams with the same part number will indeed have the same timing value.

What I meant is that there is no "standard" timing value for *all* camshafts, or *all* CIS camshafts...

-Wayne

[82targa]

Thanks for clearing that up, now I think I understand.

~Damian