Mike J

Shoot, away for a few hours and it gets solved - nice work Andreas (but I would have guess it, right.. LOL - but you win!)

Juha suggested testing the compression yesterday at 1:51PM, so he also deserves a bit of credit - and i thought we talked about that before?

I did not remember you mentioning using an IMPACT gun on the pulley - bit NO-NO - I NEVER do that because of the chain loads and it can cause skipping, screwed up timing, etc.

It can be your problem, and you can time the cams in the car, but you will need to take the cam covers off and valve covers - luckily its a 95, so you should have the older style gear clusters. You will need a few specialized tools as well - like a dial gauge, a P9191, manual chain tensioners, and a solid rocker to get the timing adjusted ( I have all this stuff if you want to borrow it).

We can do a quick visual check though - your #1 intake valve should be depressed about 0.6 - 1.0mm when your pulley is at TDC on the intake valve stroke - so the OPPOSITE of the compression stroke, or where the spark plug is firing. You can do a quick visual on this, as you approach the TDC intake, you should see the intake valve slightly opening. Of course, you will need to take off the upper valve covers.

Do you want me to come down and help you time this puppy? I am tight for time, but might be able to come down last Saturday night, and we can work on it Sunday.... you get it all stripped and i can coach you through. Or I can talk it through with you on the phone or via skype - will PM my number.








Cheers,

Mike

axl911

Generous offer Mike.

If you have a leak down tester, bring it also.

You may want to do a leakdown on the engine to check if any valve is bent.

Jeff96-993

Help my understanding here... on a '95 the cam sprockets are doweled, and on all models the crankshaft sprocket is woodruff keyed to the crank. So the only way to lose cam timing is for the chain to jump. With the engine off, there's no oil pressure at the chain tensioners, so it makes sense from that perspective.

Still looks funny that #1 & #4 measure zero, and the rest above that. I thought if it just jumped a tooth or two that all of them would fall to the same lower level. Something else amiss?

Juha G

I agree with your reasoning; It is possible that the chain "jumps" on the sprocket, especially if you are turning the crank into the wrong direction (i.e. opening the king bolt) as you have slack on the tensioner side of the chain and the crank is able to turn a bit before the chain is tensioned, thus bringing a slack on the un-tensioned side (that is usually under tension because the crank sprocket is pulling the cams). Since there is no tensioner, the chain will be pushed out a bit and can very easily jump...

IXLR8

I don't use an impact gun...period!!! The only time I will use one is when I have a rusted/seized-on fastener on my daily driver that goes through some very severe winters and road salt. After well over 25 years it may have an hour of use on it, if that. I don't even use one for wheel nuts/bolts.

Anyway, if that is the issue, the winner is Travis because he'll be on the road shortly, depending on what is found.

mcipseric

Someone please develop a screen play! Great story.

993 Rennlist is one wonderful place! You guys make me feel honored to be associated with such good people.

race911

I think a few of us were zeroing in on it. Which is why I always say go back to the basics of the internal mechanicals. Seen too many screwy things happen.

Sadly, tough to think that a re-time is going to solve anything. Been there too many times on early engines that puked tensioners, and thinking maybe, just maybe we can get it bandaged back to health. Especially sucks at the track, for a guy who wasn't towing. And that was most everyone way back when.

For the record, I'm not averse to using an impact gun on the pulley bolt. IF the flywheel is locked. (Steve, or anyone else who's done mega numbers of engines and isn't commenting here can cringe, but it's worked for me.)

I'm having a flashback here to one of my unsolvable moments--why a freshly assembled (though from used parts) engine lost compression on startup. It had Ford intake valves. One of the only sets of heads I didn't do myself as I was time crunched, and the machinist wasn't a 911 guy. Had him set the spring height, and do it all. Something screwy in the stem-to-guide clearance that manifested itself on startup. Wasn't costly, just a time waste.

JPP

Ha. Brain good!

MDamen

What an adventure.
Travis, you can read up on Mike Js cam timing procedure in his engine rebuild story on Pcarworkshop.

http://www.pcarworkshop.com/index.php/Cranking_it_up
http://www.pcarworkshop.com/index.ph...timing_Part_II

Mike J

While there is the ability to use a key, many 95' do not use the pin to lock the sliding sprockets together - so the slippage can be at the camshaft nut, not the chains skipping. I have heard of this happening due to impacts that came through the shafts. It can also be the skipping.

Next test, as discussed, is to check #1 and #4 intake valves for the proper timing. It will be approximate since the engine still has the stock hydraulic lifters and the tensioners. Best way to measure is with a solid lifter in place, and the tensioner replaced with a took to load the chain.

Cheers,

Mike

race911

This is going to take the discussion off topic, but it's being discussed...........

I was looking at semi-torn down 3.6 and 2.7 engines here practically next to me when it hit--how much torque can an impact gun apply to "shock" the cam timing? Is it more than drop throttle from redline in 1st gear? How about a high speed spin, where the engine is rotating 5-6K "forward", and then is shocked into counter-rotating nearly that speed in the opposite direction? I've had personal experience with both, not to mention witnessing it in life or on track, with no ill-effects. Only thing I can think of is that the 3.6 tensioners aren't pumped up. And then you've go the pin/no pin issue on the later 3.6s.

Mike J

I do not think any of the 993's have the dowel pins - the only reason the cams have woodruf slots and old style sprockets is leftover parts as they started 993 production.

I suspect an impact is much sharper hitting than a fast climb in revs. As far as reversing the engine, there are spots like the clucth disk and flywheel that will absorb a bit of the peak of an impact.

With an impact gun, especially with no crankshaft pinning, the shock is very direct and uncushioned.

At least that is my understanding.

Cheers

Mike

AOW162435

Interesting Pelican link

Interesting Rennlist link


Andreas

race911

I was talking about a fast decline in revs, magnified by doing it in 1st gear.

I'll be freely corrected by someone who's experienced it, but in a spin you have the potential to go from 6K+ forward to at least 4-5K backward. That's a 10K net shock to the system, in reverse rotation. Which means the chains are running in their slack position counter to the idler wheel (and tensioner).

I THINK the first 993 engine I took apart had pins. This was pretty much when they came out--a new car was wrecked and a friend picked the engine up for his track car. (I think he sold the trans for under $1K, since who could use a 6 speed 15-16 years ago?) I know it was the first hydraulic lifter engine I had my hands in, as we were told we didn't want that for the track.

Mike J

So maybe the first 95's had the pins - and I know that some 96's have the key slots in the cams, and the updated sprockets without the ability to positive lock. I know that because that is what my 96' had - I backdated the sprockets, but the camshafts still had the woodruf keyway.

I still think the shock is more directly applied to the crankshaft - even if spinning backwards, there is the rubber tires slipping, slop in the drivetrain, cushioning by the clutch (especially if a DMF), slop in the gears in the transmission - all take that real peak out.

I doubt if any measurements have been taken anyway - its all anecdotal.

Lets see what Travis finds when he takes the chain covers off and we can work from there. If no pin, then likely its just a slip which has happened before. I know Gerry Woods (when I took the engine rebuilding course from him) has seen that happen.

Cheers,

Mike