Snapped Timing Chain?
 

Yesterday my engine shut down at about 4000rpm. Long story short; the engine cranks but the distributor does not turn. I pull the distributor and it looks fine. I'm thinking the timing chain snapped.
How ugly does it get if that happened?
Do the pistons hit the valves that remain open?
What else could it be?
I plan on tearing into it tonight. Can I get the timing cover off without dropping the pan?
The engine is a 1999 7.4MPI...
Thanks for the help,
Patrick

Re: Snapped Timing Chain?
 

Had this happen once, it was a broken cam

Re: Snapped Timing Chain?
 

Ditto, on the broken cam, several bent valves though, and cam and lifters.

Re: Snapped Timing Chain?
 

Can't imagine a steel roller cam breaking, but I guess anything is possible...
So, the pistons did probably hit the open valves too then?
Anyone got a Gen 6 7.4 long-block or base engine?

Re: Snapped Timing Chain?
 

Sound Like A Total To Me.your Insurance Companys Going To Love You This Year.im Afraid To Put Mine In The Water Any More This Year With All The Bad Luck Going Around.what Brand Of Cam Was It?pm Me With What Your Looking For And What U Want To Spend And Ill Make Some Call On The Island.

Re: Snapped Timing Chain?
 

I had the same thing happen when my oil pump siezed up and broke the gears off the distributor gear. Pull the dist out and check the gear.
Good news is that most internals were fine .

Bad news is that the motor was pulled and disassembled to flush out the metal. The cam was still ok. New pump, gear and gaskets and all was good for the year I had it.

Re: Snapped Timing Chain?
 

Hey ZZ,
Don't think the insurance company will cover this one...
If the engines is gone, I will be looking for a replacement Gen 6 (1996+) 7.4 or 454mag.

Bobaloo, The distributor is fine... Either the chain or cam must have broken???

Re: Snapped Timing Chain?
 

Patrick-- Sounds like you're getting pretty good advice. You may want to pull the valve covers and spin her over. Obviously if you snapped the cam there won't be a lot of rockers going up or down. If none of the rockers move, you're right and the chain broke. If it did, crank the starter and listen for a constant rpm. If the sound varies, you've probably got some bent valves because of uneven compression. Look for evidence that the valves are seating. A compression test and leakdown test should confirm what you've seen and heard. Unfortunately, even top shelf cams break. Let us know what you find.

Re: Snapped Timing Chain?
 

Thanks Lmarth,
I'll pull the valve covers first, got to do it anyway...

Re: Snapped Timing Chain?
 

I hear you Tempest, but I have cranked it over may times already.
If the pistons hit the valves, the damage is already done...

Re: Snapped Timing Chain?
 

The valve covers aren't going to tell you anything???? If none of the rockers are going up/down, the timing chain broke. If only the front cylinder's valve train is functioning, the cam broke. Please enlighten us Tempest.

Re: Snapped Timing Chain?
 

You Can Remove The Timing Cover Without Dropping The Pan.just Loosen The Pan Bolts And Pry Down Alittle.have Done It Many Times.reinstalling I Nip The Ends Of The Cover Where It Tucks In.

Re: Snapped Timing Chain?
 

Just talked to the engine builder that did my cylinder heads. He has no clue if there is enough piston to valve clearance for the engine to crank out of timing without collision. He did agree that the damage has already been done. Told me the first thing he would do is pull the valve covers, loosen the rockers, then put air to the cylinders. If she leaks the valves got hit. If not, she may be salvageable...

Re: Snapped Timing Chain?
 

Patrick-- Your engine builder makes good points. You'll have to take it one step at a time. If you're really lucky the valves didn't get bent. A lot has to do with how aggressive a cam (lift) you're running and compression ratio (dome configuration). I once saw a dropped valve just bounce off the dome of the piston. The valve hit the piston square and did virtually no damage! Keep us posted

Re: Snapped Timing Chain?
 

Pat,Just an idea but I did a timing chain and gear job once too find out it was the 10 cent roller pin that holds the gear onto the shaft that was not noticable until you put some force on it and then you could see the shaft spinning inside the gear. I know its a long shot but just thought I would pass it on because it cost me $250 and a Saturday. Good luck. Tom

Re: Snapped Timing Chain?
 

I would think that if the pistons hit valves that the engine still would not turn over so easy. I have also seen the problem that zzzzzz mentioned in his last post. I would first call mercury and ask if the 7.4MPI 310 engine is an interference engine. However perhaps he may not even know.

Roby

Re: Snapped Timing Chain?
 

had the same thing happen as zzzzzz, broken rolled pin in the distributor gear....




fingers crossed for an easy fix

Re: Snapped Timing Chain?
 

Well Guys, I started tearing into it.
Pulled the water pump and balancer before it got dark.
Have not gotten the timing cover off yet but I can see inside.
The chain is definitely off or broken. The gear on the crank is stripped.
Things are not looking good... :(
I guess tomorrow after work, I'll work on loosening the pan so I can get the timing cover off. Then I'll work at getting the valve covers off. Lots of stuff in the way.
Seeing the stripped gear on the crank has got me thinking the cam is locked up... Anyone else got a guess???

Re: Snapped Timing Chain?
 

Don't waste your time - Just pull the motor. It is going to have to come out no matter what.
It will be alot easier to pull it apart on the stand.

Re: Snapped Timing Chain?
 

Yea, I am sure things are quite ugly inside...
I'll screw around with it a little more tonight then yank it over the weekend.
Looks like my season has ended about two months early.

Re: Snapped Timing Chain?
 

On the wishful thinking side, maybe when the engine was built the assembler did not install the front galley plugs with the .060" holes. These holes are there to provide a source of lube to the rear of the cam spocket so it will not gall up on the block and seize. If this were the problem and if you have enough piston to valve clearance you may be in luck. Lot of "ifs" there, but at least a small ray of hope. Look closely at the backside of the cam spocket for signs of heat and galling.

BT :cool:

Re: Snapped Timing Chain?
 

OK Guys, I tore into it a bit farther.
Dropped the pan down and got the timing cover off.
Looks to be a failure of the gear on the crank and the bolts and pin holding the cam gear to the cam. The chain is still in one piece surprisingly...
I pulled the cam and lifters out and they look like new, other than the bolts snapped off in the cam. The oil pump also spins freely.
The piston did hit a couple of the intake valves though. I can see that they are still open when I look down the intake ports.
Next, I guess I'll pull the heads to see what the pistons look like. With my luck there will be holes in them... :rolleyes:
If I have any luck, the bottom will be OK. I have the stock cam and heads that I could bolt back on.
Any thoughts?
Thanks again for the advise,
Patrick

Re: Snapped Timing Chain?
 

What type heads are you running? My t/c broke on my engine after upgrading to merlin heads. They neglected to machine the top of the valve guides and it was bottoming the retainer. About 4 hrs later I was running @4000rpm and it broke. Of course they denied it but my very sharp machinest showed me the cause.To this day I am still warning people off of them. I told them I was going to get my money or cost them money. Sorry your missing out on the rest of the season. I know I should have checked them before installing but if you pay $1400 you don't expect to have to do that.

Re: Snapped Timing Chain?
 

Tempest,
I am crossing my fingers the piston are not too beat up... Would be great if I can get through the rest of the year with the stock stuff.

kennyo,
I was running a set of modified l-29 Vortec heads. The engine has about 60hours on it since I changed the heads and cam. I still have the stock heads and cam that came off.

Thanks for the replies,

Re: Snapped Timing Chain?
 

Piston Are Stronger Than You Think.make Shure They Move From Side To Side And The Rings Are Not Frozen.slap It Back Together With The Old Parts For The Rest Of The Year.why Did It Break?did You Locktite The Cam Bolts?cambutton Thrust Bearing What?

Re: Snapped Timing Chain?
 

No, ZZ I did not use locktite, but I will next time. Inch-pound torque wrench is not enough. They must have loosened up causing the failure.
The engine is a Gen 6, so the cam is held in place by a trust plate. The cam slid right out and the bearings look fine.
Ordered up a new timing set, and gaskets; let's hope for the best!

Re: Snapped Timing Chain?
 

I wacked all my valves in one engine last year. Your pistons will be fine. Your cam will be fine too. No need to change unless it is improper for the stock heads. Just check the pushrods. When I did mine it was all the intake valves bent and only a couple exhaust.

BT

Re: Snapped Timing Chain?
 

I hope your right BT. The cam is too big for the stock heads so I'll use the stock ones. Thanks for the advise; I will check the push rods. Maybe I'll just change them, I have another set. Should I change the lifters too? What do you think?

Re: Snapped Timing Chain?
 

You cannot use the current lifters with the old stock cam. Lifters and lobes get wore in to each other and cannot be moved to different lobes or used on different cams after breakin. Do you have the original cam and original lifters which are marked for which lobe they belong? If not, I would either continue using the current cam/lifters or buy a new cam/lifter set and breakin accordingly.

BT :cool:

Re: Snapped Timing Chain?
 

Original GM roller lifters with about 180hours...
They had about 120 hours when I changed to the 454HO cam.

Guys, I'm only looking to get through the rest of the season (20-25hours).
I'll do a complete rebuild this off season or buy a new base engine.

Thanks for the help,

Re: Snapped Timing Chain?
 

I agree with blue thunder.Additionally, If you insist on putting this thing back together, I'd make sure any sharp edges on the pistons where they were struck by the pistons be smoothed out to avoid hot spots or stress risers whereby the pistons would crack.

Re: Snapped Timing Chain?
 

I pulled the heads off last night.
3 belt intake valves.
Pistons show no signs of the collision...
The gaskets and new timing set on order.
Pulled the stock heads and cam out.
With some luck she'll be running again next week.
Thanks for the help guys,

Re: Snapped Timing Chain?
 

Will Your Reprogrammed Ecu Work With The Stock Cam?

Re: Snapped Timing Chain?
 

Hey ZZ,
I have two ECUs... One I sent to AZ Speed 3 times for recalibration. The other is stock. Funny thing is, I have been running the stock one all year.
AZ Speed just could not get it right. Volvo's stock program worked fine other than the 4800 rev. limit. and 600rpm idle.

Re: Snapped Timing Chain?
 

Is'nt it funny how things change when you get curious, If you were to rely on someone else your season would be over.

Re: Snapped Timing Chain?
 

Amen to that!

Re: Snapped Timing Chain?
 

Pat,
bringing up your old subject here.

what did you use for your timing chain, the single chevy one or did you upgrade to a double roller?
thanks
kevin

Re: Snapped Timing Chain?
 

I bought another single roller chain and gears.
The single roller chain set-up is the same on the ZZ502, 502HO, 454HO, and the L-29 454.
The chain is not what broke. The bolts and pin holding the cam gear on sheared off, then the crank gear got stripped of its teeth. The chain was still in one piece. I would say the single roller chain is plenty strong for a stock or slightly modified engine.

Re: Snapped Timing Chain?
 

You too had problems with AZ speed :eek: