Questions about changing my timing chain

[syclone98]

My car died last week and wouldn't start again but I *thought* I had solved the problem tonight. I changed the crank sensor and went through all the tests in the "No Start" tree to verify that it should have in fact started up:

- I had good fuel pressure
- I changed the crank sensor and checked the cam sensor
- I verified that I was getting both spark and injector pulses
- I did a compression test and got 90psi on all cylinders
- I pulled the plugs to dry them off from the excessive cranking as they were wet

After putting everything back together and trying to start it I got excited when there were some signs of life in that the engine seemed like it wanted to start. After trying that for a few minutes, without any making any kind of unusual sound the motor started turning over way too easily.

The first thing I did was check again for spark and an injector pulse - I was getting neither. After pulling the oil filler tube and seeing that the rocker arm wasn't moving at all I concluded that the chain had let go.

So...I'm going to replace the timing chain but had a few questions first:

1) Should I go single roller with a tensioner or double roller? (The car's only going to be a daily driver).

2) When the car died last week, I'm pretty sure that the timing chain had only slipped at that point but not actually broken yet as I was still getting spark and an injector pulse. Since it only broke while attempting to start it tonight, how much of a chance is there that I may have actually bent a valve?

3) If there is a chance of a bent a valve, is there any way to check this first before changing the timing chain? The reason I ask is that I'm pretty close (but not quite there yet) to rebuilding the motor anyway. If the rest of the motor is probably still okay then I'll just replace the timing chain for now but if I most likely did bust up a valve or two I'll probably just start tearing it down for a full rebuild.

4) Anything else I should be concerned about or watch for?

Sorry for the length of the post and thanks in advance for your feedback and suggestions.

Christopher

 

[SouthernCal GN]

How many miles on the motor?

If you're going to go thru the engine soon, just use the stock nylon setup with the tensioner. It's quiet, and you'll probably get 100k service from it.

You'll want to drop the pan and clean the nylon chunks (from the old timing set).

If you're going to just freshen the engine up, now may be a good time to do it.

 

[syclone98]

It's got about 110K on it.

Any idea on how to check for possible bent valves?

 

[SouthernCal GN]

Try this; loosen the rocker arm assemblies; feed compressed air into each cylinder, and check for leaks (air coming thru throttle body).

 

[syclone98]

Excellent idea, thanks.

 

[johnnyttype]

im pretty sure that a broken timing chain on our cars will not cause bent valves because it is low compression, dished pistons, which make it a non-interference engine. never hurts to do a leak down test though!

things that would change this are more valve lift, higher compression ratios, etc. hth

 

[psycho6cyl]

Is his compression a lilttle on the low side?

 

[Chuck Leeper]

Is this a Syclone or a TR? If it's a TR you can have piston to valve contact.
The 90# compression is likely due to the cam being out of time, it could also be from bent valves. I'd go ahead, pull the rockers, and run a leakdown.[SOCAL's idea!]

 

[Just a Six??]

To give you some hope I slipped a tooth a the track. After I got it started again I drove it home 75 miles & parked it. Tried to fire it up & KaBoom Backfire!! Tore the motor apart & only damage was the chain & sprockets, rest was fine. There is light at the end of the tunnel for ya!

 

[scottyb]

My chain let go on a cold startup (tensioner pad came off, and the chain sawed off the few cam gear teeth that remained). Valves were ok, but I bent 2 pushrods. The car ran notably better with a new chain - probably because the old one had too much slop in the cam timing.

 

[syclone98]

It's a Turbo Regal and I'm hoping that I didn't break anything. If I did though it'll just give me an excuse to keep going and have the whole thing rebuilt.

If it wasn't for the fact that I just pulled the motor out of the 86 to have it rebuilt, I wouldn't think twice about doing this motor too but since I only have so much of a "play" budget and my Corvette is also giving me a bit of grief, I'm going to try and get a few more miles out of it by just replacing the chain for now.

Just A Six - How are things up there in Toronto? I've been in California since 95 but I'm originally from that area, Hamilton to be exact.