WillyC4S

Hello,

I recently purchased an '86 951 and was establishing a baseline for maintenance by doing all the belts, seals, water pump, ... one thing I'm learning from this is get the flywheel lock (tool # 9206).

I had all the belts, sprockets removed except for the crankshaft bolt and it's associated sprockets/pulleys. Was waiting last to tackle that problem. The balance shafts and camshaft were set on TDC already. I jammed the flywheel with a punch (@ TDC) and attacked the crank bolt. I checked the lock of the flywheel by pulling on the breaker bar and it seemed locked. Then proceeded to put on a 3 foot pipe extension on the breaker bar to remove the bolt. One strong pull and I heard a crack (the bolt loosening up), but in the process, the punch had fallen off the flywheel and dropped to the ground. I started to loosen the bolt (counter-clockwise) but the flywheel was moving, so I re-inserted the punch again ... this time without putting it back at TDC. Anyways, long story short, I may have been off by as much as 180 degrees (half turn counter-clockwise from TDC) during the latter part of my crankshaft bolt-removing session.

So now I'm wondering if I may have bent any valves in the process. Normally if you turn over the crankshaft by hand and encounter a piston you'll feel it ... and stop. When you've got a breaker bar it's a little hard to tell if it's the flywheel lock or the valve that's holding crankshaft from moving (in case the punch fell off the flywheel).

Bottom line is ... can you check for any valve damage without having to fully remove the head from the engine? I'd rather not remove the head if I don't have to. I would appreciate any advice on this situation.

Thanks,

*****

Perry 951

Put it all together and do a compression check. That is about all you can do.

If you are lucky, that 180 degrees missed the open valve. It realy does not take much to ding it enough to not seat right.

WillyC4S

Thanks Perry951, that suggestion had come across my mind as well. I'm trying to figure a way to see if there's a problem now before re-assembling the whole darn thing; if so I could do the removal now while everything's apart, essentially lessen re-work.

Do you happen to know which valves are open at TDC? I think firing order is 1-3-4-2 for our vehicles.

I'm also wondering that if you back off half a revolution that's basically 2 cylinders going
off (I believe that would be cyl. #2 and #4, moving counter-clockwise). Which other cylinders are up during those times? Are 2 pistons up and 2 down at any one time (i.e. TDC #1 is up on ignition, but #? is up on exhaust ...)?

Thanks,

*****

Steve Lavigne

Do a leakdown test. Obviously you need to have the timing belt and pulleys installed to do this. Typically it is good to do a leakdown test on a warm motor, but it should give you a decent indication.

Still, you really won't waste that much time by putting it back together and doing the compression check. The only real issues if you need to remove the head will be having to drain the coolant and re-tension the t-belt

WillyC4S

Steve,

Good point about only re-tensioning the belt. I forgot that you only need to loosen the cambelt and take it off the sprocket for a head removal; nothing else gets touched. Makes it a bit easier.

Does a leakdown test also check the exhaust valves or only the intake valves?

Thanks

Steve Lavigne

The leakdown test is done with the piston at TDC. That means that the piston is at the top of its stroke and the intake and exhaust valves are closed. If you have significant leakdown, you can check the exhaust, intake, oil fill tube, coolant, etc. for hissing air. There was a thread posted today in the main 944 forum that has some links to more information about leakdown tests.

Dave951M

If you were really off by 180, there is a very good chance you dinged the valves of 2&4. Do a leak down and cross your fingers

WillyC4S

Thanks everybody for all advice. I'm going to do the leakdown test and see if it's a problem. I'm thinking that I didn't go an entire 180 degrees, but more like 90 degrees (which should only be half-way up or down) so I should be OK.

I'm learning so much ... looks like two crankshaft cycles for every one camshaft cycle.

That darn camshaft bolt (stripped and had to Dremel it out) and those Woodruf keys in the cam, balance and crankshafts. Nothing's easy to work on in this car ....

*****

951and944S

*****, darned, a little late on this one I guess, but measure the height of the valve stems against each other with the cambox off.
A bent valve won't close completely, leaving the stem lower than the rest.
Take care when doing this to not cause damage, but tap each valve stem top with a hard plastic object (large screwdriver handle) and listen for one that is out of tune with the rest. Make sure to test four exhaust and four intake valves separately (they have different sound). All intakes and exhaust valves should sound the same when tapping with the object of choice, if one sounds flat, it's bent...

<img src="graemlins/beerchug.gif" border="0" alt="[cheers]" />

Dave951M

I noticed that you had your camshaft bolt strip out. One piece of advice here for anyone working on any 12pt internal stuff, clean out the bolt first, repeat, inspect bolt for crud, repeat cleaning if necessary. Seat the internal 12pt socket into the bolt head, tap it down gently with a hammer to seat it, key here is gently. Put wrench on internal socket turn, making very sure that the camshaft, bolt and internal socket stay lined up respective to each other as you do it. Follow this method and you'll strip out far fewer bolt heads.

Dave

WillyC4S

Thanks 951and944S and Dave951M for all the good information. The part about the valves is quite interesting. I'll have to check that and see what I come up with.

For the 12-pt (triple square) on the cambolt, I used an impact wrench with a universal joint to clear the front part of the vehicle since the camshaft axis is slightly below that part. I stripped the bolt AND the 12-pt tool; it must have been the universal joint which allowed too much flex during the operation. I thought for sure that the impact wrench would get the bolt out in the first blow .... took about 5-6 attempts with the last one stripping the bolt.

Thanks again for all the help folks.

*****

Steve Lavigne

Twice I've stripped the cambolt. Due to several other failed attempts to remove broken bolts, I ended up taking the cam housing to a machine shop and they cut the bolt head off for me.

In retrospect, make sure that you have a high quality 12 point socket (snap on or equivalent) and use a air ratchet which allows you to torque the bolt in a single plane so that the socket stays fully engaged.

Dave951M

I would advise against any air tools for this operation because with a manual tool, you can feel what is happening before you really screw up. An air tool just lets you do it faster. Just my opinion.

WillyC4S

I'll say that if I had to do it again (when I need to change the belts next time) that I would probably not use an impact wrench. I'd probably go with the route recommended by Dave in that you get better feel and more control over the actual "breaking" of the camshaft bolt when it comes loose. Also the slowness of the manual operation should help you keep the socket and cheesehead bolt aligned thus preventing the stripping effect from a mal-aligned tool.

Then again, these cheesehead bolts strip pretty easily and can't take the torque a normal hex-head bolt can take. If it wasn't for the darn distributor design being bolted to the end of the camshaft, Porsche would have put a normal hex bolt in there; only way to put the rotor extension and other mechanisms in-line with the camshaft axis and still have a bolt securing those items is to use an internally-driven bolt (allen or triple-square) rather than an externally-driven bolt (hex). It's a neat and clever idea that's really hard on maintenance in a real-world situation, as we all know by now ....

*****

Steve Lavigne

The reason I mentioned using the air ratchet was due to my putting an undesired torque on my manual ratchet when I tried to remove the bolt. If you don't have an assistant, you need one hand for the wrench holding cam gear and another hand for the ratchet. What you really need is a hand holding the counter-holding wrench, one hand on the end of the ratchet, and one hand on the ratchet head to keep it engaged and aligned properly.

Using an air ratchet works, but a standard impact that doesn't fit with a u-joint is definitely a poor choise, and would negate my intention of using the air ratchet to keep it aligned properly.