Viking12

I put new timing belt on my 1999 rx300 all marks are correct . Tried to start only cranks . I'm getting white spark on front 3 plugs . I'm getting fuel . Will not start with ether . No security codes no engine codes . Disconnected battery have no clue

salimshah

Welcome to ClubLexus.

Not sure if this is your problem, but the 4 stroke engine will have 2 points where the crank will be on the mark. The mark needs to be aligned with cylinder 1 at TDC.

Salim

Viking12

All 3 marks are TDC

Drcoffee

Yes but is number 1 cylinder on the compression stroke or exhaust stroke? The cams turn once for evey two turns of the crank. If you are not careful, its easy to lose track of position of the crank when doing the timing belt.

salimshah

Without getting technical, I understand that the 3 marks are matching.
BUT
You can spin the crank 360 degrees and still match the mark. If you spin yet another 360 degrees, you will match the mark. Only one of the two positions is correct for 4 stroke engines. To avoid this potential confusion one should not touch the crank shaft once the Timing belt is removed. [you can nudge it but not spin it and if you spin then make 2 circles.

I just gave you one possible reason why the engine would not run. If you are sure that you did not spin the crank-shaft or you only spun in times2 then this is not your problem. If you recall spinning the crank one time around or odd number of turns then this is your problem.

Exercise of finding if your engine is in compression TDC of #1 requires observing the valve position (cams not pressing any intake or exhaust valve of #1) or looking at the timing. Task much easier on straight mounted engines and rotor distributor. Hopefully some one can give you pointer(s) on how to determine this easily on RX. Expert mechanic, who knows the timing sequence can infer by observing the 2/4/6 cam position and tell when the 1 will go to TDC as they spin the crank around. Sorry, I dont have this knowledge to share.

technical details:
Limiting discussion to Cylinder 1 only, in a 4 stroke engine reaches TDC twice for a complete 4 stroke cycle. Once in compression stroke (spark -- the one we are interested in timing) and the second time during exhaust stroke.

Drcoffee

Salim,

I believe you and I are mistaken. The mark on the crank shaft when matched to the block shows that the #1 piston is at TDC. Same for the cam gears. If he matched all 3 marks when he installed the belt, then he is set correctly. Its only once the belt is installed does the crankshaft and camshaft position matter.

OP,
did you by chance disconnect the crank or can position sensor? Did you rotate the crank 2 full revolutions to make sure the timing marks were still correct? Since I wasn't there, I am only guessing. What about the tensioner? did you pull the pin to release the tensioner on the belt?

Viking12

I might have to rotate the cam 360 . I was thinking about that

salimshah

No Dr. Coffee we were correct on this one ... there is no gearing in the crank shaft and TDC of 1 with respect to crank will match on compression and exhaust stroke. The cams are larger in gear dia (number of teeth) and they spin 1/2 turn for each crank turn and thus once matched will always match.

When the engine is put together the first time or after the belt breakes the tech goes through the process of ensuring the compression stroke of #1 is the condition of timing marks. When I do the belt replacement I just match the marks and then do not touch the crank.

I am not sure if OP is 360 degrees off or is in sync. Only he can confirm.

Crank shaft needs the magnetic cog to trigger crank-position sensor. Maybe some sensor wire was left un-connected or pinched.

The two crank turns at the end of the timing belt ensures belt is moving correctly and there is no interference any where.The very first time I did the timing belt change, I was expecting the belt marks to align again and only by logical reasoning I concluded that the marks on the belt are only to be used when you hang the belt. Rest of the time the marks on the cams and the crank are to be observed.

Salim

salimshah

No my fried cam rotation will not get you any different results. See my reply to DrCoffee for details on ratios between cam and crank.

If you ever need to turn the cams then make sure you do not use force ... interference engines cause the valve(s) to hit the piston head. RX in certain conditions (high rpms) can become an interference engine.

I would remove the plugs so that I am fighting the compression on any piston and turn the crank with light force.

Salim

Drcoffee

if he rotated the cam gear 360, he would be back at exactly the same place with both valve closed on the #1 cyl. Same for the crankshaft if the mark on the gear matches the block, the piston is on the up stroke. I think you are confusing whether the belt is on or off.

if he had the marks (all 3) lined up when he put the belt on and he didnt jump a tooth, he is okay. Once the belt is on, then the cams turn 180* for every 360* rotation of the crankshaft.

think about it. The mark on the cam gear is a 1:1 with the lobes on the camshaft. If the mark is up, then the lobes of the cam are off the valves. Same for the crankshaft. If the mark is up, the piston is on the up stroke.

the only way this gets muddled up is if marks are off by a few teeth when the tensioner was released.

Drcoffee

these are interference engines. You could not have rotated the cam gear 360* without causing valve contact on a piston. Check your sensors. Im guessing you disconnected one and forgot to reconnect it.

go to walmart and get the $20 OBD2 code reader. You may have temporary codes set that hasnt triggered a light on the dash.

salimshah

We have had long discussions on RX-300 engine. Folks have had timing belt that broke while driving and had no valve/piston damage. The V8 vvt would for sure have collision. On RX at low rpms (when vvt-i has not advanced a lot) the valve clear the pistons.

Note for OP ,,, please check everything and do not force anything.

Salim

Drcoffee

thats good to know.

Viking12

tore everything apart timing is right on checked all wires talked to a 30 year experience Lexus mechanic dealer . He said u cannot be 180 out as long as u are TDC you are good these motors are not interference . Still won't start keeps cranking did compression check , very good still have no clue . Also put on a snap on computer no codes

salimshah

You can not be 180 off with with the crank on the mark but you can be 360 off. If he used 180 and meant 360 then trust me the mechanic dealer has been working with lawn mower engines. He needs to understand 4 stroke engines. Please look up an encyclopedia and keep in mind there is no gearing between main pulley and the crankshaft. Your problem can be be some other thing, but science behind 4 stroke engine is that you have 2 TDC for a complete cycle and ONE of them has a spark with valves closed and the other has a exhaust port open and no spark.

Compression test is useless check after T belt change ... assuming nothing broke. A timing test or verification of spark would be more useful.

If you have air compressor and fittings, you can confirm that TDC on 1 with spark would happen with the valves closed. If the TDC is exhaust cycle then the air compressor should leak out of the exhaust. If air comes out of the exhaust, simply turn the crankshaft 1 complete revolution. Confirm that 1 then keeps the pressure. That would be the good TDC to align marks.

Salim