1986 Porsche 944 NA-Engine Won't Hand Turn

[fitzpac3]

Background-Did a complete rebuild on the engine including having the block bored and honed. Cylinder head rebuilt. Put it back together and it fired right up last Saturday...wife lost the bet

Now comes the sad part. Went to start it on Sunday and the motor rumbled a bit and died. Tap the key a couple of times and got a starter click. Checked battery and it was full. Had a funny feeling to pull the timing belt covers. I could see that the timing belt had come off the pulley and was wedged against the balance shaft belt.

Pulled the belts off and discovered my timing belt tensioner was rubbing on the back of the cover. I used a small spacer since my oil pump did not have a boss, when I should have used the strange looking bolt that came with the oil pump hardware kit.

Got new belts and a new tensioner. Put everything on yesterday and set the timing. Turned the key and essentially got a click, almost like a bad battery or starter, which are both almost new. I tapped the start solenoid and checked the battery (fully charged)/nothing. Hoping I burnt off the starter when the timing belt jumps off track.

Went and pulled the plugs, made sure the car was in neutral and manually turned the motor over by turning the crank bolt. Was able to turn it about half a revolution and that was it. Locked up. I reversed the wrench and was able to turn it back the other way, until once again it wont turn.

Not sure what happened but I imagine it could be a bent valve or worse a spun bearing. The engine never started the day the belt jumped off track. I cannot imagine it being that bad.

HELP!!!!!!!!! What do you think is preventing the engine from hand turning?

[Fraser_Crenshaw]

Unfortunately the "rumbled a bit and died", followed by "timing belt had come off the pulley" is pretty indicative of interference. However I would assume even with a bent valve the motor would turn freely after you reassembled everything properly with new belts and tensioner...

[fitzpac3]

The engine does turn by hand almost one revolution, but then it stops. I have not forced it. I just reverse it. So what do you think is stopping it? Possibly a bent valve or two that won't seat?

[kdjones2000]

You're valves are bent.

Take the head off and fix things....

[fitzpac3]

I will start tomorrow. I hope my new pistons are not damaged. Thanks

[IdahoDoug]

Ack. Sorry to hear this, and hope to hear good news when you get it apart. Expect to see some piston damage which is different from destroyed. These are inanimate lumps of metal and can be repaired, but your worst enemy is the frustration you're feeling on the time. You thought you were going to be driving it this weekend and you're not. Summon up your strength of character and soldier on! I've been there and done that on a few projects in 45 years of hobby wrenching, so I can relate.

Doug

[fitzpac3]

Doug

Spot on. Thought I had a touch down and a flag was thrown. You think it killed a piston? They were brand new.

Thanks
Casey

[IdahoDoug]

Nope. I think you'll be bummed at having some denting, but it will be the much more replaceable valves that will hit the dustbin. Over the years, I've opened a few engines that were running fine and found everything from valve dents, to impressions from a random bolt that clearly fell in from a carburetor butterfly valve and spent some time in there before exiting. If a valve head snapped off and ground around the cylinder walls and got wedged between the piston and head it will be different but you'd know that happened. Your hair would still be standing on end! Heh...

[fitzpac3]

Pulled the intake today. Valve closest to firewall bent along with second one closest to firewall. Attached our pics from second one from firewall. Also used a magnet to pull a small piece

Thanks!

[pfarah]

Ouch...

[IdahoDoug]

Ow. Just reread your original post - thought it had just turned over and made noise and you stopped, but realized it started by noting the words "..and died". Bummer. That's a lot more force.

Not looking forward to pictures with head off, but let's keep our collective fingers and toes crossed.

[fitzpac3]

UPDATE:* Pull the head and the pictures speak for themselves.* One valve completely apart.* Chunk of the head missing near valve seat.* Probably lost.

MY BIGGEST ISSUE is cylinder 3.* Posted some pictures of the piston and the cylinder wall, which I had honed a bored my Lindsey racing.* Towards the top of the cylinder there is a small scratch.* Please tell me I'm good and wont lose compression :-(* And the piston is ok with the valve marks

[IdahoDoug]

Well a lot better than I thought we'd see. The head should go to a pro for sure. That will be a financial decision of "fix this, vs start over with another head" and up to them.

On the cylinder wall - I'd clean that up and run it. People who like their opinion to be synonymous with perfection will tell you it needs to be fixed, but I've seen enough perfectly running engines opened to find even deep scores in the cylinder walls to say that. It will be how to clean it up without putting abrasives into the rings that's the challenge. Doable.

The piston is a question mark. Not the valve mark circles, but the divot close to the edge. If it's mushroomed the edge outward you could have some contact with the cylinder walls that is again - not a big deal. It's a smaller deal if that's above a wrist pin end, and a bigger deal if it's 90 degrees from a wrist pin end where more piston/wall contact occurs in normal operation. But I personally would run it if I got a bright light and could convince myself the piston top is not flared out either at all, or barely.

Curious you said the block was actually bored? I thought these cylinder walls had a coating like nikasil or something and could not be bored.

Anyhow, overall I think you skated. Take a shop vac and try to vacuum very aggressively in the #3 to pull stuff up out of the seam between piston and wall. Tape a straw into a crevice tool to get a powerful suction in a tiny tip. And I have some ideas on how to clean up the cylinder wall. You'll also want to clean up the tiny points on the piston top to reduce hot spots that can cause preignition but that's also doable.

[fitzpac3]

Thanks Doug. Yes-I sent the block to Lindsey Racing before this disaster and they bored the block .5 mm and recoated the walls. Brand new wossner pistons. Now one looks likes it got in a fight. I will get a new cylinder. Probably look at 944 online for a significant discount since they advised me on the spacer for the oil pump stud that held the timing belt tensioner that failed. I will clean the are well and run it. Thanks!

[kdjones2000]

Get another head and clean up the other stuff.

[mytrplseven]

Is it possible to get just one replacement piston?

[fitzpac3]

Thanks KD Jones2K! I will talk to Mike Lindsey on the phone tomarrow and probably get the new head and try it. Much better than pulling the motor again and sending it from Hawaii to OK for another hone and bore.

Mytrplseven-I imagine I can get another piston from Lindsey racing. Current pistons were all balanced and the rings were put on them. Way beyond my skill set. All I had to do was install them.

[walfreyydo]

I would get a used head, cut/lap new valve seats, clean up that piston best you can to make sure its not contacting cylinder wall, and run it.

Tough luck my friend, but all is not lost!

[IdahoDoug]

Last year, I bought an 88 Toyota Supra that had been sitting for 19 years in a garage near Mount Rainier, WA. It had blown a head gasket and then sat. Two cylinders had rust rings and the engine did not turn. Determined to keep it numbers matching, I put a shot of Kroil on each piston top for months until I was rewarded with movement without damage (I was worried primarily about breaking a ring and scoring the cylinder). Once the pistons were out, I measured each cylinder with the traditional 6 points and it proved to be stellar. Someone took very good care of this girl before the HG blew.

So now I had two ridges to deal with and this is getting to your situation. I needed to find something very close to the cylinder diameter that I could glue some super fine sandpaper to in order to knock the ridge down (high spot) without danger of creating a low spot. After weeks of randomly noticing round things in hardware stores and carrying calipers whenever I went on errands (heh) I found a PVC drain cap. So I knocked the ridges down a few weeks ago and now I will use a hone to prep the cylinders for new rings.

So, there may be a slight high spot there from the damage and IMO you might determine if you can feel it (aluminum pushed into that score mark may flow into a high spot on each side of it). Perhaps you have an original piston around, or piston ring you can use a bright light to examine it or snap off a section of an old ring and see if it "rocks" across the damage - indicating a high spot. If there is no high spot, I'd do absolutely nothing. If there is a high spot, you might consider a strategy like mine to knock it down.

Nothing massive - just a film of grease on the piston/wall gap to catch any debris and a few minutes work is all I'm thinking. Just so there's not a high spot and so there's nothing to catch the rings.

Probably more words than needed here but some thought starters for you. I agree - run it.

Doug

[fitzpac3]

Pulled the head and cleaned up the cylinder did some light polishing on the top of the piston.* Head was destroyed.* Purchased a rebuilt head, which arrived Friday looks great.* Put it on yesterday with a new head gasket.

NOW FOR THE WEIRD PART- Install the cam tower with a new gasket.* Used the cheese head bolts specified for the cam tower.* Realized the bolts bottomed out before tightening the cam tower to the head.*Thought it may be the extra long pins that came with new head so I put the shorter pins in off my old head.* No can do.* I ended up cutting about 6 mm off the cheese bolts, which appeared to work.

​​​​​​​Any idea what happened here?* I did test the bolt height on both old and new head with a digital gauge.* The bolts went in about 6 mm farther on the old head.* Maybe a machining issue with the new head?