Firstly I guess the default position would isolate all the passages. The only flow of oil in this situation is the small amount through the metering port which will provide low pressure to the rockers to lubricate them.
When the engine rpm passes the high lift trigger point the solonoid is energised and the spool valve connects the main gallery pressure to the rocker shafts, this then pressurises the rocker shaft sufficiently to drive the locking pins in the high lift finger followers into place thus switching cams. The solonoid will stay in this position as long as the engine is above 6000rpm.
When the engine speed drops back below 6000rpm the solonoid is energised in the opposite direction and the rocker shaft ports are momentarily connected to the relief port and the internal pressure is dumped as quickly as possible to reduce the chances of the finger followers engaging on the edges of the locking pins which was a major worry for toyota. This position can only be maintained for a split second whilst the transition back to the low speed cam takes place, then the solonoid with go back to default.
Next week we’ll pull the other end apart, The VVTi solonoid has two pressure outlet ports(advance and retard) and a relief.
Firstly I guess the default position would isolate all the passages. The only flow of oil in this situation is the small amount through the metering port which will provide low pressure to the rockers to lubricate them.
When the engine rpm passes the high lift trigger point the solonoid is energised and the spool valve connects the main gallery pressure to the rocker shafts, this then pressurises the rocker shaft sufficiently to drive the locking pins in the high lift finger followers into place thus switching cams. The solonoid will stay in this position as long as the engine is above 6000rpm.
When the engine speed drops back below 6000rpm the solonoid is energised in the opposite direction and the rocker shaft ports are momentarily connected to the relief port and the internal pressure is dumped as quickly as possible to reduce the chances of the finger followers engaging on the edges of the locking pins which was a major worry for toyota. This position can only be maintained for a split second whilst the transition back to the low speed cam takes place, then the solonoid with go back to default.
Next week we’ll pull the other end apart, The VVTi solonoid has two pressure outlet ports(advance and retard) and a relief.
thanks a lot for the explaination, it makes a lot more sense than the simple “on/off” description could be found on the SAE paper you quoted (which was the one I read before).
IMHO this explaination is also helpful in the cam wear issue:
if the spool valve sticks in the “open relief port” position, this could explain the problem…
Just on a little tangent here but there has been a lot of talk about the lowering of cam change-over point. The 240s all have a change over in the 4000s and now the reflash will allow N/A cars to run a 5500 change over point. First of all the change over seems to be done according to the oil pressure the ECU can be set for a specific pressure which will mean a certain rpm. I heard some people were worried about oil pressure issues if the change over point was too low � this seems not to be an issue since ECUs are being reprogrammed etc. Have I got that right and are there any things to watch for when lowering the changeover point.
If the spool valve where to stick in the relief port open position then it wouldn’t be able to engage the high speed cam. The valve only has one moving part.
Jamie, switching the cam at a lower speed will increase the engine oil flow but at 4000rpm the PRV will be already open and regulating at a ~fixed pressure. The big thing in preventing the engine spitting a rod out is all to do with the lubrication of the small end and the centfugal effects which occur inside the crankshaft. This all comes into play over 6000rpm so there shouldnt be any change.
If the spool valve where to stick in the relief port open position then it wouldn’t be able to engage the high speed cam. The valve only has one moving part.
Sorry, I didn’t mean it as a relief port stuck open all the time (high lift cams weren’t going to be under stress at all) but basically a two position switch: either relief port or high pressure camshaft feed.
I didn’t think of a mechanic sticking issue, but a software “bug” instead.
You be surprised what you can think you hear in an engine. Ed I would get the top off and have a look (or get a hand) you cars has higher mileage than most S2s
Thought i would update this thread with what the state of play is with my car.
The car was taken to the Dealers yesterday for inspection of the damaged cam, and this information sent to lotus.
Lotus have agreed to pick up the cost of a replacment cam & followers and the labour charges.
Aparently Lotus have only seen this Issue once before on an early development car that had very high milage, and investigation showed it to be a hardening issue with the cam.
I have to say that the dealer has been excellent in assisting me with this issue, and kept me informed of every communication with lotus in resolving this issue, anybody in the north of the country i can recommend the service that HHC at Hexham provide.
I should get the car back next week, fingers crossed it will be running alot smoother.
Hopefully Bob with have a similar experience with his dealer where i know his car is currently being check over.
excellent news Phil, I do hope Bobbly (short for bob corbishley, sorry mate )
gets the same resolve.
Thats excellent news, my dealer is going to call out the Lotus field engineer too but said from the start that he would expect Lotus to be very good about it.
Once thats fixed I only need to worry about the bodywork getting patched up…
As someone who had an early failure with a toyota engine (unrelated to the problem described in this thread), I have to say that both the dealer & Lotus dealt with the issue really well, & the car has run very sweet ever since.
I spoke to Matt Becker just after collecting my repaired car, & just has others had said before, a failure of this engine is very rare. The original development cars had no significant failures.
It’s a fair bet that the Celica’s engine install doesn’t get the same degree of thrashing as in the Lotus’ though.
It’s a fair bet that the Celica’s engine install doesn’t get the same degree of thrashing as in the Lotus’ though.
Very true, I can’t drive my Exige without hitting 2nd cam. I once thought about driving on a full tank of petrol without going above 70mph or hitting 2nd cam just to see what mpg I could get. Truth is, after four months of ownership I haven’t managed it yet…and probably will never manage it.
I came from an RX-8 and had to razz the nuts of that to get it to go fast. Still love the noise and aspects of a N/A engine, these forced fed turbo’s sound cool but will probably ruin my driver experience.
Just a quick update. My dealer rang me last monday to say that they’d eventually found time to be arsed looking at my car and that they’d taken it out for a spin and looked at the cams and came to the conclusion that it was just fine…
I cant believe how incompetant they are, I specifically told them which cams were wrecked and sent them packing. I had to ring them back last wednesday at which point they confirmed that they had found the problem and were working on it.
They rang me yesterday to say that their technician (they only have one?!) is off work long term sick.
Now what do I do??? They are trying to palm my car off on the bodyshop now to replace the rear clam after I was pranged back in october. I doubt they can take it just like that. I haven’t driven my car (other than taking it to paintshops or garages) since october 13th.
I’m really sorry to hear that your having problems Bob,
As you know mine is all sorted, i had no hassle getting mine sorted out, Lotus excepted that it was a failure that had not just happened over night, my car was off the road for a week tops and that was mainly because i could not find the time to collect it,
PM me if you require the details of my claim against lotus, I have the photos of my cam and followers, the dealer still has all the bits in a box.
Have they given you a car ?, i was offered a car at lotus’s expense. for the time it was off the road, even if you dont use it it puts pressure on the dealer to sort it out.