shark13

So I really don't have an excuse other than I procrastinated and procrastinated to the point where now the timing belt on my 99 RX300 is I'm pretty sure broken. I know there is quite a bit of debate as to whether the engine is an interference or non-interference engine. That is not my question though. I am going to replace my timing belt, water pump, and crankshaft seal, and hope for the best. If there is more damage I'll address it then.

My question is regarding the timing. Obviously both cams are out of timing with the crankshaft. I would assume that piston 1 would be set to top dead center but what piston should be set to top dead center on the other set of three? Is it just a matter of setting both pistons at TDC, making sure the hash lines on the cam gears line up with the engine, and then doing the same to crankshaft?

If there are other details I am missing I'm am listening.

Thanks,

Marc

salimshah

Before you go investing too much, do a compression check.

When you align the crank shaft at the mark you are ensuring that piston #1 will be at TDC and piston#4 will be at its appropriate position. The cams control the vales. Since we have a 4 stroke engine the TDC can be one of the two .. in compression stroke or in the exhaust stroke. The timing (spark) needs to be on the compression stoke and that is what you need to match to.

So if we mix it up the possibilities and you simply align the marks [crank, cam1 and cam2]
1. Everything is ok
2. Crank is 360 degrees off.


You need an experienced mechanic or if you want to do it yourself, you may have to open the valve cover and note the valve movement to understand which stroke the piston #1 is [can be inferred with compressed air and checking the exhaust for air flow.

Salim

PS: 360 off means you need to rotate the crank 1 full turn.

shark13

Hello Salim,

Thanks for the information. I suspected there was another factor I forgot to take int account. I've rebuilt the head of my Honda Civic (lapping valves, valve seals, etc, rebuilt rocker arms after the came apart) and it was the same with the only difference that it was a single overhead cam design as opposed to the RX300 dual cam.

I'll open the valve cover the watch for the compression stroke. To confirm, on the exhaust stroke the piston will rise to the top and the exhaust valve will open. Then the piston will drop and as it rises a second time that will be the compression stroke. When it reaches the top of that compression stroke this is where I will ensure that cam gear lines up exactly with the engine case, then repeat on the other cam, and then finally set the crankshaft to line up with the engine

Does that all sound correct?

Thanks

salimshah

I fell into the same trap regrading cam#2. Then I realized that the top cams rotate exactly once for two turns of the crank. So the top never goes off sync. So if you are the at mark on cam1 then the valve + timing will be compression TDC .. the crank may be correct or off 360. The other thing to consider is that the mark on cam2 does not mean cylinder 2 will be at tdc of compression stroke. But the valve train of the bank 2 will be right ... it will be where it needs to be when piston#1 is at TDC compression.

If you have air compressor, you need not open the valve cover. Just send compressed air in chamber #1. If you are on exhaust TDC, the compressed air will exit from the exhaust.If yo are at TDC compression, the compressed air will have no escape ... [just the leaks by the piston].

Salim

shark13

Salim,

That makes sense because piston 1 (bank 1) and piston 4 (bank 2) are not going to fire at the same time.

So in a complete cycle of the engine the cams will turn twice and the crankshaft will turn 4 times?

Is there a way to know whether the crankshaft is correctly aligned or 360 degrees off in advance?

Marc

salimshah

4stroke engine --> 2 turns of the crank -> 1 turn of the cams. [pistons move down(combustion), up(exhaust), down(suction), up(compression) --> 1 complete 4 stroke cycle)

I think you have 50-50 chance that the crank would be out by 1 turn. It was so easy when we had distributor. All you had to do was look turn the crank till the connection moved to plug #1.

this may be helpful

Salim

Bluejay84

If you broke the belt and it's zero clearance it's odds on favorite the valves are bent. Do a compression check. If you start it up and the valves are bent you run a very good chance of doing irreparable damage to the pistons, valve guides, etc. I unfortunately had a similar experience on a zero clearance Galant and it bent several of the valves. I got lucky that the pistons only showed some taps from when it went but I've heard stories of them getting gouged pretty good.

Lexmus

There is no evidence the RX300 has an interference engine.

shark13

Sorry for the further questions. I just want to ensure logically I understand this correctly. Is my thought process correct?

Four stroke engine.....cams rotate once, crankshaft twice. Lining up the cams on their marks is all that is needed for the cams. Since they only spin one rotation in the cycle there is no possibility of them being off by 360 degrees.

The crank can be on the mark but be on the exhaust stroke or compression stroke. Hence the possibility of being 360 degrees off.

It is necessary to set the pistons at TDC on the compression stroke.

The question is how does one determine whether the piston is at TDC when the valves won't move as the crank is turned?

Am I correct in my assumption that at TDC the ignition would normally take place and therefore both valves and would be closed. Following that logic if one used the balloon method to determine when air was being pushed out they could accurately know whether the crank is lined with the engine case mark on the exhaust stroke or compression stroke?

Marc

salimshah

You are overthinking the problem.

Just line them up. Release the tensioner. With hand turn the crank 2 turns gently and stop if you have resistance (compression of the engine is ok).

Fire the engine up. If you have it right it will start, if not turn the crank till marks align. Remove tensioner take the belt off, turn the crank 1 full revolution. Put the belt on. Release tensioner and turn the crank by hand 2 turns to make sure there is no resistance. Fire the engine and things should be fine.

The turning by hand is to ensure there is no interference.

Salim

shark13

This weekend I had a chance to finally tackle this project. What I found is that the timing belt did not break, and the teeth were all still there. It appears that the edge of the timing belt began to fray like a single string and wrapped itself around the spindle. As the engine spun, the frayed piece continued to separate till the point that it was completely around the spindle perhaps 1/2" thick. I removed the spindle, cut away the torn piece of belt, and checked that the engine spun freely with no resistance....which it did nicely. I also did not notice any oil leaking out of the crank seal but I intend to replace it any way.

Prior to checking the engine for resistance I took note of where each cam and crank where in relation to their reference marks. From what I can tell each one is different which leads me to believe the belt string that wrapped around the spindle caused the belt to slip a few times and get the engine out of timing enough to die. Does this sound probable?

I noticed a fair amount of oil build up to the left of the crank and found an open metal tube that ends in the direction of the oil. I have attached a picture. Is there a connection between this oil and the tube? Is this a vent of some sort or am I missing it's corresponding rubber tube?

Thanks,

salimshah

The tube/hose looks like vacuum hose going to the steering pump. Please confirm (from memory two hoses go there to complete the loop ... )

Oil in that area is typically from steering pump and hoses or a trickle down from valve cover. If you are not loosing any steering pump fluid then for sure it is from the valve cover(s) above.

Check the seals of the shaft that the belt wrapped around ... the strands can bite into the rubber.

Salim

shark13

So after way too long (solid rain for a month and a half) I have finally finished replacing the cam and crank seals, water pump, reinstalling my timing belt. Everything seems to be running well but I have two lights that are on in the dashboard. The first is the ABS light and the second is the battery.

I was really good about removing the batteries positive cable as to prevent any issues with the alternator. My guess is it's the battery as I have had the car for probably six years and it just sat for about a month and a half. When I do start the car up it runs but then when I try and restart the engine it is either weak or will not start. I plan on having the battery tested tomorrow.

Any ideas on what could be causing the ABS light to be going on?

shark13

May not be the battery after all. I am getting around 12.5 volts on the battery before turning the car on, but then when it's started the voltage drops to a steady 11.1. My thinking is the voltage dropped because the alternator is not working and the car is pulling power from the battery. Does this sound about right?

salimshah

Low voltage and or ripple from alternator can cause both the errors.

You can take the battery and the alternator to be bench tested at the auto parts store.

Salim