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 Post subject: Rebuilding Prins reducer
PostPosted: Sat Aug 27, 2016 7:37 pm 
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Gents,

Does anyone have a guide to rebuilding a Prins reducer please?

Cheers.

Nige.


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PostPosted: Sat Aug 27, 2016 9:49 pm 
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Full rebuild or just changing the diaghpram, the latter is quite easy on Prins reducers.

Simon

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PostPosted: Sat Aug 27, 2016 10:00 pm 
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Had a quick look - this might help for the video (audio probably not helpful though)

https://www.youtube.com/watch?v=W_-VE050jn4

Theres at least 3 different phases of design - And revisions from A-I of the VSI reducer if not more.


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PostPosted: Sun Aug 28, 2016 10:35 am 
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I have a later version which is leaking from the coolant elbows but checking in the shed, I previously replaced an older version (D) and bought a repair kit consisting of o-rings, diaphragms etc. I figured I'd refurbish the old one and put it back on. I used to have a PDF guide but cannot find it :(

Cheers.

Nige.


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PostPosted: Sun Aug 28, 2016 5:27 pm 
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Also worth bearing in mind VSI is very fussy regards reducer pressure, following a rebuild (that affecting spring pressure on diaghpram) it may be necessary to check/adjust pressure, the only place to see expected pressure is in software settings, though without software you could measure pressure with an external gauge before the rebuild.

Simon

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PostPosted: Sun Aug 28, 2016 5:33 pm 
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No issues with regards to software. I just wondered if you could perhaps give a brief step-by-step?

Cheers.

Nige.


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PostPosted: Sun Aug 28, 2016 7:10 pm 
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Full rebuild / just changing the diaphragm, to what extent do you intend on rebuilding? If most of the way it's worth remembering you don't get all parts in a rebuild kit and even if you did there can be wear on the housing itself... a rebuild isn't guaranteed to fix every problem. Tbh if seals aren't leaking there's little point in changing them.

You did mention water elbow leaks.. Is yours the type where both elbows are secured by a single plate that is secured by a single bolt? That type just pull out, best to use a slight twisting action. Seal is just an O ring in a recess on the elbow, elbows a push fit.

Simon

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PostPosted: Sun Sep 11, 2016 7:27 pm 
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Well I managed to open one side of the reducer but the other side (with the torx bolt in the centre) would not come off at all. The torx bolt turns all the way in both directions but the cover does not budge. How does this side come off?


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PostPosted: Sun Sep 11, 2016 7:33 pm 
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The torx bolt right in the middle is probably how you set the pressure. I'd expect the spring to be on the other side of it.


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PostPosted: Sun Sep 11, 2016 7:41 pm 
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And looking at the repair kit it seems the same bolts run all the way through from one side to the other - I don't know the Prins VSI reducer at all, but from previous experience of taking others apart the heavy ends left inside can form somewhat like glue. It may be just held on with that, especially if its cold as suspect it will be if your rebuilding the old one.


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PostPosted: Mon Sep 12, 2016 11:29 am 
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Is the torx bolt you mention the pressure adjuster or were you referring to the mounting stud on the other side? And is that a torx or allen socket?

Agreed with Bri on heavy ends acting like glue but even without that effect rubber seals / diaphragms can retain the covers after the rubber has been tightly clamped in position for a long time (rubber around bolt holes etc can be squeezed into holes). Could be that either/or of those effects is holding the reducer cover in place, in which case would just need a bit of persuasion to come off... but don't do anything to scar the mating faces, prying is a bad idea, tapping usually works. Careful not to tear rubber in case it continues to stick while taking the covers off.

Simon

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PostPosted: Mon Sep 12, 2016 11:54 am 
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It may help to run some hot water through it as well.


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PostPosted: Mon Sep 12, 2016 12:32 pm 
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Brian - wil try some hot water.

Simon - I was referring to the pressure adjuster.


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PostPosted: Mon Sep 12, 2016 1:03 pm 
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Yes, the cover should just pull off - no part of the pressure screw mechanism should retain the cover.. the pressure adjuster is sealed against the cover with an O ring but the only part of the pressure adjust mechanism that attaches to the cover is more of a flat disc (inside) than a shaft.. The disc may be stuck in the cover slightly due to the O ring but between the the disc and diaphragm there is pretty much only a spring - The pressure adjust allen / torx screw will probably be retained in the cover when the cover comes off and not affect the cover coming off. Increasing pressure setting will put the spring under more tension and could aid getting the cover off. For re-assembly, on the one hand decreasing reducer pressure setting lowers spring tension so can make the cover easier to refit, on the other hand a setting other than minimum pressure can help you locate the spring properly (but keeping spring located properly while putting the cover back on isn't as tricky on these reducers as it is on some reducers anyway). When the cover comes off you'll see how the pressure adjust mechanism works, since you've been turning the pressure adjust screw it would be a good idea to make sure threads in the disc will/are engage(d) before bolting covers back in place, as turning the adjuster too far can cause the threads to completely unscrew coming off the threads (again the threads don't in any way hold the cover to the unit).

VSI reducer £25 in need of repair http://www.lpgforum.co.uk/viewtopic.php?f=29&t=14155, got a few myself too!

Simon

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PostPosted: Thu Dec 01, 2016 1:17 pm 
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In the end I just replaced the o-rings that were leaking at the coolant inlet and outlet points on the reducer and have been running fine for some time but now (and only on gas) I keep getting really rough running. I've checked the error codes and get:

multiple cylinder misfire with fuel cut off
misfire cylinder 6 with fuel cut off
misfire cylinder 8 with fuel cut off

I've cleared and the errors come back, sometimes changing the cylinder numbers on which. Everything runs perfectly on petrol.


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PostPosted: Thu Dec 01, 2016 4:54 pm 
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Hmm, the 'with fuel cut off' bit makes a bad situation worse from a diagnostics and drivers perspective eh! Is this on a Merc?

Maybe the colder weather brought this problem on - In Prins software you can set time to changeover if reducer is below X temperature etc. In colder weather, too short a time setting here could mean the reducer is too cold to work properly. This could apply particularly on a Merc or something with a similar heater water flow circuit if the reducer is plumbed in a certain way (delay in flow until climate control sees fit to allow flow). What happens if you drive on petrol until the engine is warm enough for the heater to work nicely and then manually switch to gas?

In some cases vehicles stop reporting specific cylinder misfires after the 'multiple cylinder misfire' code is generated, so if it runs OK on petrol and it isn't always 6 and 8 that misfire on gas it'd be a fair assumption that injectors / ignition are not to blame and something more generic is at fault... Such parts include standard components such as lambda probes, cam/crank sensors, maf/map sensors and LPG parts such as reducer, ECU, pressure/temp sensors, injector emulator switching unit(s). Reducer over pressure situation could cause this type of problem but if affected cylinders are only on one bank that might narrow it down to one lambda or only one of the injector emulator switching units.

Have you confirmed all is well on petrol with a scanner?
Simon

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PostPosted: Thu Dec 01, 2016 5:04 pm 
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It's an old 5 series V8. Just driven 150 miles on petrol and everything is dandy - no errors code and fuel trims spot on. The moment I switch to gas it runs lumpy and the EML starts flashing - even when the car has been running for an hour and the coolant would be plenty hot.

Cheers.

Nige.


Last edited by N_Willmott on Thu Dec 01, 2016 10:28 pm, edited 1 time in total.

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PostPosted: Thu Dec 01, 2016 10:27 pm 
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Plugged in a code reader and lifted the bonnet. The gas injectors seem to be ticking a lot more than normal and fuel trims are all over the place when on gas (but perfect on petrol), so I am assuming the gas injectors on the cylinders with errors are at fault??

Cheers.

Nige.


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PostPosted: Thu Dec 01, 2016 11:27 pm 
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It might be worth a try with some IC12 injector cleaner or similar - it may be that they are sticking slightly, probably worth a try with that before trying anything more drastic.

100ml one linked below - theres a 50ml bottle, but they are out of stock at the minute. Available elsewhere as well.

http://www.lpgshop.co.uk/ic12-injector-cleaner-and-lubricant-100ml/


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PostPosted: Fri Jan 27, 2017 10:24 pm 
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By way of update, I replaced the Keihin injector I thought was faulty and everything has been running great.

Some time has passed and I am getting differing LTFT on Bank 1 (-3.9) and Bank 2 (-10.9) but on petrol the banks are similar and both around -2.9. Does anyone have an idea why the 2 banks would differ so much on LPG?


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