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Slow boost


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A bit of head scratching, the bush for the spindle of the "Flapper Valve" wastgate had definitely moved causing  the valve to sit to one side and not seal, but showed no sign of wanting to budge a second time.

A bush within a cast iron exhaust impeller, in logic will probably be made of a metal that expands faster than the casting, so I figured I'd put the whole thing in the freezer (it's good to be a bachelor) took it out tapped it back in line, job done !

 

Now all I have to do is get the remnants of the studs out of the manifold so I can bolt the intermediate pipe back on ! Ironic that now I realise I didn't have to take it off in the first place. There again I could not have diagnosed it without dismantling it.

 

I have the inevitable broken drill bit stuck in one, any ideas ?

Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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Thanks, I was about to peruse my Dremel catalogue, just hope my local Bunnings has a selection in the morning.

Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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Well I finally got them all out, did in a number of drill bits, killed the Dremel (not happy, it was expensive)

I now have the down pipe back on, Allan Bolts and nuts, should get the turbo back on tomorrow. I leak tested the wastegate, came up better than I expected, ie sealed.

The silver lining ? I have improved my drill bit sharpening skills, I had a jig sharpener which I always thought was useless, I can now do it better freehand.

Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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That would be a fix, just to be safe I took the wastegate back to 10 psi, but all is good, no leaks, sounds fantastic, and goes like hell.

Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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Well done Roger. I did my Dremel in the first day I had it. Applied too much pressure and stopped the motor - didnt work after that . But managed to put everything back and got another one, bit cheeky but I am now much more careful when using it.

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  • 3 weeks later...

Hey Roger

 

Thanks for posting this! I've got the exact same problem!!


I've been suspicious of low boost in my Esprit ever since I bought it, but not having anything to compare to, I was never sure. I have a home-made logger which I've been using to measure boost pressure/rpm etc and always found that I never got anywhere near full boost until 6000rpm. I'll attach a boost-rpm curve to show what I mean.

 

This weekend I decided to add an oil pressure sensor to my logger and one thing lead to another, as it always does with a Lotus. To get to one thing you have to take off 3 other things. And I am now looking inside my turbo and seeing exactly what you saw - the waste gate spindle/bush has slipped sideways and so the waste gate is permanently open! At least the turbine blades are all
in one piece...

 

So all this time I've been driving a naturally aspirated Esprit :(


How is your repair holding out? Any sign of the bush slipping again?

Steve

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here's the picture of my waste-gate, supposedly in the closed position!!post-3342-0-63725400-1359179678.jpg



And here are some traces from my logger:

First one shows a couple of accelerations up to 100kmh. The boost spikes over the rated 65kPa only when you take your foot off the throttle - that's because I've got the sensor on the turbo-side of the carburettor, so it sees the boost building up against the closed butterflies, but before that it barely gets ot 60kPa even at 6000rpm.

post-3342-0-65882600-1359180013.jpg

 

The second one shows boost versus rpm. Only starts to boost (and only weakly) above 4000rpm.

Its going to be interesting to see how this changes when I get the waste gate fixed!!

post-3342-0-07384300-1359180157.jpg

 

 

 

Steve

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Yes, exact same problem ! I can save you some work, Get some freon or similar freezing agent, spray the turbo body and you should be able tap the spindle into place, no need to take it off.

Be prepared for Cape Canaveral !

Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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Thanks Roger,

I am going to pack it inside and out with some dry ice and give it some time to soak through to the bush.

Do you know what the bush is made of? (I can't see it at all...)

If its bronze or brass it should shrink almost twice as much as the cast iron housing.

Steve

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My guess is some sort of bronze. What I can confirm is it shrinks much faster then the housing when frozen. I could not budge it until severely cooled. The a couple of solid taps it was back in place.

Resist taking the turbo off, you end up with almost every stud broken.

Life is like a sewer, what you get out of it, depends on what you put into it. (Tom Leahrer)

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  • 2 weeks later...

Got the turbo off fairly easily and did the freezer trick, but no joy with tapping the bush back into the housing.

Tried to disassemble the waste gate valve/spindle arrangement, but its not going to happen without cutting the spindle. Its just too long to get out any other way. It looks to me like these things are assembled by shrink fitting of the parts, something I just don't have the equipment to do. So I am shopping for an exchange or replacement unit...

Steve

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  • 2 months later...

Well I finally got my turbo sorted. Bought a new one from SJSportscars. Cheaper, easier and faster than trying to get someone here in Perth (Oz) to repair the old one.

 

Finally found the time to put it all together and drove it for the first time today...

 

Certainly feels like a turbocharged car now! Wow.

I've missed a lot of excitement over the last few years!

 

Here's my before and after boost curves...

 

 

BoostComparison.pdf

Steve

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