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12th September 2015, 23:50 | #11 |
Gets stuck in
Rover 75 Saloon 2.5 Join Date: Jul 2012
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What I wrote was "The front sprockets are NOT "keyed" to the camshafts like the rear ones are"
And they are not. As I read it the OP was wanting to understand how moving the front sprocket with the timing tool would impact on the rear sprockets. The fact that the front sprockets are not keyed to the camshaft but float on a hub is in my view the critical thing for the OP to understand. To the OP, I hope that you have the answer you were seeking. |
13th September 2015, 15:20 | #12 | |
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MG ZT 190 Join Date: Nov 2011
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Thank you all for your input on the matter.
Quote:
The timing is done on the front and the tool is actually holding the camshaft itself, not the sprocket (when unbolted ofcourse). The small freedom of the sprocket rotation is used to fine tune the position of the sprocket in regard of the teeth of the tensioned belt and therefore the crankshaft. The above leads to the conclusion that the timing - a correct positioning of the camshaft is done by the tool. The tool is rotating the cam to the correct angle and holding it there while you put on the belt. The different tool plates (2.0L, 2.5L, 2.5L 190) rotate and hold the camshaft to different angles. The main question turns out to be: if a correct 190 tool plate is used, what is the position of the rear sprockets? Will they align? What if a wrong tool is used? I'm sure this is true for standard 2.5L as Phil-T4 wrote, but is this also true for the 190 when the cam is rotated to the degree dictated by the tool? If this will be confirmed it would mean, for all engine versions in perfect timing the marks on the rear sprockets align, and taking into account that the marks will align at only one specific camshaft angle, then it would seem that even when no tools were used and the mechanic simply checked the rear sprocket marks alignment, then the correct camshaft angle was set - no matter if it is a 2.0 or a 190. Another question: I've read on this forum that "on the 190 the timing is different on the rear bank". What's that all about?
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13th September 2015, 17:08 | #13 | |
same car since 2005
2001 Rover 75 2.0 v6 Connoisseur Saloon Join Date: Nov 2006
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Quote:
As I understand it , the purpose of the floating hub in the sprockets is to allow the teeth to be aligned with the belt and permit some movement of the sprocket when the belt is tensioned , while the camshaft is all the time held correctly by the tool. As I said before , it is quite clever in use
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13th September 2015, 18:01 | #14 |
Posted a thing or two
MG ZT 190 + and MKIV Supra Join Date: Jan 2009
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Blimey Im glad I bumped this question
After reading all the comments I now have a better understanding. As the OP said thanks to everyone for their comments. I sit in the no need for the timing tools side of the garden but we will see when I do the job
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Jon C Living the dream MK IV VVTI Tiptronic TT Toyota Supra MG ZT 190+
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14th September 2015, 11:01 | #15 | |||
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MG ZT 190 Join Date: Nov 2011
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I am afraid that simply aligning the marks on the rears when in safe position is ok to make the timing work but is not enough to get the full power form the engine.
I managed to dig up a post from the other site by the user 1955diesel who worked at Rover and designend the timing mechanism. Our member Kaiser discussed the issue of the rear marks with him: Quote:
Quote:
Quote:
To align the inlet cam to the exhaust cam, you use the rear sprocket markings. This assures that one cam angle is synchronised to the other cam angle and that's what rear marks are for. But to do the actual timing - aligning the cams to the crankshaft in most accurate way, you unfortuanatelly need the tools to do so. You can get away with just setting the marks on rear sprockets to align when in safe position and the engine will work fine as this is the balanced setting and is perfectly fine to make the engine work correctly. If however you wish to take advantage of the research done by the factory in fine tuning the position of the specific cam you have and therefore get the full power available with that cam, use the tool to set the cam to the proper angle when cranshaft in safe position. This is the only way to know what is the best angle for the camshaft you have. Unless ofcourse someone with the tools () can attach them to the cams on the front and make a detailed documentatin of the angles of the marks on the rear for each engine version, then peopople without the tools could set the same angles. Untill then, tools it is.
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14th September 2015, 22:02 | #16 |
Posted a thing or two
mg zt Join Date: Mar 2014
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I firmly believe (but have no proof) that the inlet cam needs advancing around 10 degrees to improve torque on the 190. The reasonfor saying this is the inlet valve on the 190 opens at tdc - this is just about unheard of on anything other than lawnmowers. I belive it was done to improve emissions for the 190 with the increased valve timing.
Also, as further evidence, look at the 16v k series, closely related in many ways, again opens the inlet valve earlier. Usually, advancing an inlet cam will, up to a point improve midrange torque, at the expense of top end bhp. And who needs 190 bhp anyway? Its only there as a sales gimic, in my opinion. There is one possible fly in my theoretical ointment however, the poorly designed exhaust front pipe, it may be that the back pressure from this could reduce the effect of increasing overlap, but its a slim chance. Also, the ehaust timing would need to be adjusted to keep it where it is. Huw |
15th September 2015, 01:17 | #17 |
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75 Tourer 2.5 Auto, 1.8T, 75V8ZT Join Date: Jun 2007
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If you know your engines, you will also know there is not one set timing that is best. There is a timing recommended from the factory, which according to them provide the best compromise.
I remember my discussion with that person, and I also remember he opted out on several occasions. He might have designed the system, but he did not strike me as being fully aware of what was going on. But, as they say: De mortuis nihil nisi bonum So to sum up. There is no chance in hell that the marks align by chance when the right timing is done. It is designed like that, and that is common for any engine produced I have ever come across. The timing is on, when two or more marks align. The problem is, if that is the case for all models of the engine. That answer can perhaps be answered by researching if there are different parts numbers for the sprockets for the different models. If so, the only difference could well be the position of the marks. It does not take much to provide the correct marks when manufacturing, but it introduces more numbers and spare parts. They could simply have made several marks and marked them clearly, and the problem would be sorted, but this is the logical choice. That seldom seemed to be what Rover did.
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17th September 2015, 22:40 | #18 |
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MGZS 180 Join Date: Aug 2009
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Maybe the keyway's in the cams are counter rotated the same degree as they are advanced at the front on the 190? i dont know but it would enable all pulleys to be the same across all engines.
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18th September 2015, 11:27 | #19 | |
same car since 2005
2001 Rover 75 2.0 v6 Connoisseur Saloon Join Date: Nov 2006
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Quote:
As far as I know , the sprocket wheels are all the same .
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