12HT Boost Compensator Diaphragm (1 Viewer)

[relaxedcruiser]

Hi folks,
my first post here went into the classified forum - so I´ll try it again.

missed some ponys inside my good old 12ht so started to search for them.
As I had checked and ruled out many other possibilities before I focused on the boost compensator.
The culprit is most definitely in the diaphragm itself. Not enough movement in it. ....my one despite feeling quite allright seems to be a bit on the stiff side and has probably hardened out as it did not pass the test which is described in the manual: Apply 1.36 bar or 19,7 psi and achieve 4-5 mm of movement at the rod. If less discard the entire boost compensator.
My one is way off - I can only achieve a max. of 2.8 mm stroke when I applied the 1.36 bar with the guide bushing turned so far out that the spring just hold a tad pre tension.
The parts catalogue is showing only 22013-68151 which is the basicly whole top part of the govenor, I don´t know whether this is still available - but for sure it is or was rather expensive.
After searching the net for a while I found exactly nothing about it.
So my question into the world is: Has anybody replaced that diaphragm with an other part or knows the Denso part no.?
As my 60 is still going quite well - (it freed up many ponys reducing the spring preload on the diaphragm by turning the so called guide bushing 3/4 of an turn out) - i´m looking for annother old one to show it at the Bosch Denso Keiki Zexel or Lucas shops around.
Maybe someone has done it before and knows already more...?
Cheers from downunder

 

[relaxedcruiser]

No one here who has ever replaced the diaphragm on the 12ht ?

 

[IanB]

If you bring the pump number to a diesel injection shop they should be able to look one up for you.

 

[remy]

The spring is very stiff. Almost not compressable by hand. Also very hard to replace when the pump is on the engine.

 

[relaxedcruiser]

Thanks for your replies Ian and Remy,
after taking the inlet manifold away you are able to unbolt the complete boost compensator body very easily for dismanteling. I´m looking currently for an old one to search for the new diaphragm while driving my truck - It´s my only transport right now. Or get the Denso Part no. from somneone here.
In annother tread here I read that there is a website where you can convert Toyota to Denso part numbers. The search goes on...

 

[IanB]

Being as your in the NZ/AUS part of the world, why not talk to a pump rebuilder? They should be able to set you up with no issues.

 

[relaxedcruiser]

I already had the pump at a Denso/Keiki/Bosch Diesel shop for checking over.
I was slightly disappointed when they called and stated that my pump is in good health and everything is withhin the factory specs - only a bit overfuelling - which was clear as I tweaked the screw a bit to give the engine the much desired liveliness - not much, just so much that she is happy running with 0.7 bar / 10 psi of boost without excessive smoke. They asked me whether they should bring it back to factory specs.
Yes why not I said - knowing the the power is just an allen key and a spanner away. And it would be good to feel how the engine would run in complete factory settings.
The outcome was very disappointing as the engine had lost quite a bit of grunt. Out came the 3mm allen key and the 10mm spanner to open up the fuel delivery like before - It run a tiny bit richer but not much. I was then able to unscrew as many revolutions as I wanted but there was no further response from the pump. I called the diesel service and they said that everything was allright on the testbench. Since the truck was running now sort of alright just not that grunty than before I left it like this as you can unfortunately not play with your toy and everyday vehicle all the time.....Months later I took the inlet manifold off and found out what I had suspected already. The pump shop had adjusted the fuel at the so called guide bushing. This bush is efectivly the trust for the spring which sits behind the boost diaphragm. After releasing 3/4 turn of preload from the diaphragm the engine ran like before the pump shop was working on it. But the test for the diaphragm itself shows that the rubber is hardening and movement of the diaphragm is already restricted. So two things were restricting the liveliness, the adjustement and the diaphragm - first thing sorted ....
That is why I´m just after a new diaphragm now.

 

[Talos]

A bit of a thread Resurrection but I don't find anything else on the subject.

Did you end up getting a new diaphragm? and was there any difference?

 

[relaxedcruiser]

Hi Talos,

yes - got a new diaphragm - will come back with the news tomorrow as I was just about to close the laptop and go sleeping. 11:30 pm this side of the world.

 

[relaxedcruiser]

I got the new diaphragm from the diesel specialist shop - it came in a blank little plastic bag - I believe a aftermarket part.
When I replaced it I did in the same time a little modification to the body. As there is no possibility to adjust the preload of that diaphragm with the pump attached to the engine. The Inlet Manifold covers the access.
I tapped a 1/8' NPT into the housing and now have a nice inspection hole to adjust that star wheel in no time at the side of the road.


After I had the new diaphragm installed I did the test as described in the Manual.
It works absolutely fine with an syringe and an check valve alongside with my little industrial boost gauge.
Interestingly I was not able to get the stroke of 4-5 mm as per manual - although it was a bit more than with the old stock one.
I have to check in my notes in the workshop but I believe it was about 3.5 -3.8 mm with the new one
However - I fitted the boost compensator back with the same preload like it was before (counted clicks until the spring is becoming loose), finetuned it on the road and it runs fine since then.
Maybe the aftermarket diaphragm is limiting the stroke ? Maybe the manual has a bug ? Anyway - truck runs fine and I am able to adjust the pump into overfuelling / black smoke. I hate that but it tells me that the diaphragm is able to develop more stroke in relation to the given boost than necessary.
Talos - I hope that I could give you some information...

Pic above shows compensator in initial test - before tapping...note that I already marked the spot when it was all still attached to the IP

 

[Talos]

Great to hear and thank you for the response, I had a problem in my HJ61 that I couldn't get it to smoke at all, always suspected the boost compensator, will definitively check it out when I have time.
Did you get any reference on the diaphragm? part number or manufacturer

 

[relaxedcruiser]

No - the diesel shop supplied it after I gave them the Denso part no. from my IP.
Came in a blank plastic bag and looked different material wise than the original. It may be a generic part. Have to check whether I can find a pic from it.
Take the inlet off to access - thats realy the easiest way. You will get it off the pump, but it's difficult to engage the pin inside the IP without taking the top inspection cover of the IP off.