88 Surf 2.4T & roller rocker head Right ti ho then.
In the past when speeding up through the gears, at around 2300rpm to 3000rpm, theres been a very definable amount of "boost" pressure.
Mmmm Reset the tappets via factory method & spec's & now theres no d3efinable "boost" effect. It's pretty even all through the revs . So . WASSUP with that!
Ok, what I suspect is that correctly setting the tappets has effectively advanced the valve timing by THAT little bit. Now, I know this wouldn't normally effect a petrol engine but there is a rather large difference in combustion pressures (average 120psi petrol verses 470psi for diesel L engine) Hows that for an idea & this for a solution.
Reset the tappets from the factory 14 ex/10 inup to 16 ex / 12 in or even 18 ex / 14 in to retard the valve timing slightly
When I did it the tappets the 1st time, I screwed up & made them really loose but it still drove that same way with definable boost.
intrade,
Mar 21, 4:21pm
umm incorrect adjustment of the valves will burn em out over time , i would check if the cambelt is set correctly notch is below the pulley all easy marked .Also i would more suspect that you knocked the hose off somwhere for the boost controll to the top of the fuelinjector pump or something . rwther then the valve clearance having anything to do with it.
mrfxit,
Mar 21, 6:44pm
Cam belt was done about 20K ago & hasn't altered anything in performance since Mmmm yea but no to the hose's, checked that all the hoses were in the same place today. Also only had to disconnect the vacuum pipes on the inlet manifold to get access it's really odd that from the original settings to the loose settings, it still had that "boost effect" but the moment I had the settings correct, it all smoothed over. Still starts /idles & stops as per normal hot or cold. Would love to pop a boost gauge on it but don't have 1 here & they aren't cheap for what they are
kazbanz,
Mar 21, 7:07pm
Mrfixit-An old trick with bucket n shim tappet settings was to set them right at the very limit of maximum clearance when cold.The bike would rattle like crazy till it warmed up and the clearances were bang on optimum -Moral of the story-Check your clearances hot mon and see if you are in the correct range.-you I think will be suprised
mrfxit,
Mar 21, 8:48pm
Adjustments were done hot each time (well slightly cooled after a 1km run each time) didn't feel like burning myself on hot engine parts .getting to the cam. The roller rocker tappets are adjustable just like a std english push rod motor.
On the old english tappets, it was very common to have to reface the rocker valve face because of pitting against the valve stem but on the 2L-t the adjustment pin is about the same size as the valve stem. Might have to look in to that to check for a wear dip which would upset the final measurement a tad. Would be a right royal pain to have to strip the cam to "adjust" that bit of wear on the valve tips
mrfxit,
Mar 21, 8:52pm
I have no idea on what percentage of degree's the cam would shift via tappet settings but do clearly remember that in the old days of adjustable tappets, over loose or over tight tappets could suck power & fuel from petrol engines fairly easily
skin1235,
Mar 21, 9:24pm
adjust them from the roller end dave sequence,
,50 blade on valve, tighten, check zero at roller/cam, loosen, fit 14 on top o 50 and tighten, check roller/cam is still zero, remove 14, check roller cam again, should be about 18 recheck that, it maybe 18 or 19 or someother value, whatever it is that is the value at the roller cam when the valve is set right remove all blades, set each from the roller end at the found value
old trick to get around hollow tappets and domed valve ends due to wear
even made a spanner socket and bar with a screwdriver through the middle and a dial /protractor on the screwdriver, set the protractor to zero when lash removed ans simply open the tappet required degrees, found the degrees from above method ie 50 and desired ( say 14) in tappet closed til tight, remove 14 and note degrees of turn to tighten on the 50 set them all the same as specs required, no error in valve lash
skin1235,
Mar 21, 9:27pm
will be different for every different cam profile depends on rate of lift angle and rate of change a 3 degree lag on the valves would also alter optimin timing by 3 degrees too, timing has to happen with piston in right place AND valves in right portion of cycle, being diesel it only complicates it more, errors are not so forgiving etc
skin1235,
Mar 21, 9:31pm
after a while you get to know each thread and can immediatel set them without major mucking about holden 186 were touch and back off 22 seconds for exhaust, 18 seconds for inlets, boss once check with a dial meater, found all the lash to be accurrate, never checked again( by then I'd worn the protractor figures off and used seconds on a clockface
mrfxit,
Mar 22, 6:53am
Mmmmm yep thanks for that Steve. Yep should have remembered to cross reference on the roller end but haven't had to deal with roller rockers or for that matter, any adjustable tappets for many years. I get the feeling that it's been many many years since it may have had any engine work done & probably not even this level done before since not far off the end of the factory warranty. I presume you can see where I am coming from about the change in boost effect!
smac,
Mar 22, 7:21am
You kinda seem to be judging what is right or wrong by this 'boost effect'. How do you actually knowyou've lost power! You may have actually gained back power at other points in the rev range, giving a less 'peaky' power band. Might FEEL less grunty but actually delivering better power over wider rev range.
mrfxit,
Mar 22, 1:04pm
Have done a few very common trips (for me) recently, out to Huntly a few times with & without a trailer& over to Cambridge with & without a trailer & also been down to Rotorua a few times since I did the tappets. Torqueis definitely down across the rev range & previously that "boost effect" was very definable in 2nd & 3rd gear between approx 2100rpm & 3200rpm when at approx 50% to 100% throttle (mostly 100% ish) It had always been there in the 1000rpm range for the last 3 years.
Towing & climbing hills is a struggle now compared to before. What I have gained is the ability to rev higher in 3rd gear with usable torque compared to before,thats only really usable on flat roads & no load but the previous lower rev torque was far more useful.
mrfxit,
Mar 22, 1:15pm
I call it a "boost effect" because in a diesel, that boost power band is normally fairly subtle compared to a turbo petrol engine. Remember the average petrol engine would be running something like 130 - 140psi compression & this diesel runs at around 480psi, so any boost effect is very different to a petrol engine Remember also that diesel engines don't have much of a combustion chamber so in my theory, any valve timing could have a dramatic effect on performance. Will reset the tappets compensating for the wear & get back to this thread when done (probably next week sometime.)
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