How to Rebuild a Wastegate

Note: as with all my tech tips... you use this information at your own risk and expense. I don't claim, or pretend, to be a mechanical expert. I am merely a guy who has been doing a lot of learning during the rebuild of my car and through these pages I try to pass on some of what I have learned to others in the same position as I am. I hope you find something in these pages useful... but you use everything you find here at your own risk. I take no responsibility for any negative outcome. If you are unsure of your ability to put this information to use then I would suggest you consult with an expert.

For this particular page I will also assume that you have a basic knowledge of how a wastegate works. At the time of writing this does not have a write up on wastegates but hopefully they will have one soon. One day I may attach a basic lesson on wastegate function.

Ok... on with the good stuff.

Background: For my current project I picked up a used Blitz Twin turbo kit for my 1JZ engine. It consists of twin KKK-K26 turbos, twin external Blitz wastegates, and associated piping. Before I installed the exhaust manifolds and wastegates I figured I would be smart to have them cleaned up and coated. I sent the units off to a local coating shop for a polished ceramic coating.

Before and after ceramic coating:

At this point I have to admit I am an idiot. I did ask if the coating process involved dipping and was told that "No, it is a spray on process". What I didn't know was that after coating the wastegates would go into a bead polisher to be shined up and this IS an immersion process. I should have capped the hose fittings on the units before I sent them in but I didn't... and the result was two wastegates that were full of hundreds of ceramic polishing beads when I got them back. Ooops. Whether it was the coating place's responsibility to do this won't be covered here... but I'll sum it up by saying they were great about it afterwards and more than made up for their part of the oversight.

When I opened the wastegates to clean them out I was in for more surprises. I discovered that the internal diaphragms on both units were cracked and ripped (from age) all the way around. Also the nut connecting the valve shaft to the internal pressure cup had come off in both of them and was floating free. Because of these two problems these wastegates would only be semi functional, and would require a complete rebuild before I could use them.

A lot of research and time brought me to this point... doing a full rebuild of both wastegates myself. These are older style Blitz external wastegates but the general principles should apply elsewhere. Please remember that this page is only an example of what my experience was... your situation WILL vary.

Close up view of the top of the Blitz wastegates:

- Opening the wastegate

The first thing you should know is that opening a wastegate is not as easy as it looks. Wastegates are under a lot of internal tension and must be opened very carefully. Simply undoing the bolts that hold the cap down will result in a small "explosion" of parts with a good chance that either the hat or spring will leave indentations stamped into your face. So be careful. The best method is to have someone with strong hands hold the wastegate closed while you slowly back off all the bolts a bit at a time. If you loosen all the bolts off a few turns you will see the cap start to lift and will be able to feel how much tension the unit is under by pressing the cap back down. The internal springs are designed to resist large amounts of boost pressure... sometimes 15 PSI or more... so be prepared to have to apply a lot of force to keep the wastegate together while you disassemble it.

Loosening the bolts will cause the top to begin to lift from the spring pressure:

Warning: Do not remove the bolts completely one at a time!! If you were to remove the bolts completely from one side you risk the wastegate hat twisting open and damaging either the remaining bolts, or worse, the wastegate body itself. Loosen the bolts slowly from opposite sides. Turn each a few turns at a time... in a balanced fashion evenly all the way around the top. Then have your friend hold the top down while you undo the last few turns on each bolt.

Be sure you take careful notes of how the internal parts are assembled... as with anything you take apart, make sure you know how it goes back together . Take notes if needed.

After you have successfully opened the wastegate (or survived the parts explosion) you can examine the condition of the internals. This is what I found.

As you can see some of the internals are mildly corroded but nothing that will be hard to clean up. The valve shaft nut being off was a big surprise as this would cause the wastegate to be almost nonfunctional. Without this nut in place the pressure cup can't pull up on the valve shaft and the wastegate valve would have been opening under exhaust pressure alone.

The biggest surprise however was the condition of the wastegate diaphragm. Years of high temperatures and use had caused the rubber to break down and crack/split. The picture below shows what was left. ALL of the orange that you see used to be part of one intact rubber diaphragm when this wastegate was new. As you can see the center part of the diaphragm has completely split from the ring that seals the halves of the housing. Also when I attempted to remove the center section from the pressure cup, the rubber was so brittle it almost crumbled in my hands. After separating the various pieces a layer of rubber remained "glued" to the surface of the metal parts that would have to be scraped off later.

Diaphragm remains:

Now that we know what we are dealing with the next step is to source some new parts... namely a new pair of diaphragms in my case. Blitz USA was no help in finding spare parts, but they had just moved offices and also these wastegates were not coming up in their catalogs as they were never sold in the US. Blitz said they would "check with Japan" for me, but I never heard back from them. They did however give me one priceless piece of information. I learned that neither Blitz, HKS, or Greddy (Trust) make their own wastegates, but that all of them buy from the same 3rd party manufacturer in Japan. Running with this information I had a few friends measure their wastegates and quickly realized that a large number of them have the same size housing (95mm). My Blitz wastegates are also 95mm (3.75") in diameter across the "bolt ring". Since many of the housings appeared to be a standard size, I assumed that this unnamed 3rd party company wouldn't go to the effort of creating a unique diaphragm for every wastegate they produced and that some other brand replacement parts would be a direct fit.

The final result of my search was that HKS "Race" wastegates are exactly the same inner and outer diameter as my Blitz units. Also their replacement diaphragms are easily available through HKS for an MSRP of $80 US. (Part # 1499-RA057) I ended up ordering two of these for my rebuilds. The downside is that the HKS Race diaphragms use a 4 bolt flange, where my units had 6 bolts. This would require me to cut extra bolt holes to install them, however I felt this was an ok compromise.

New Diaphragm:

Note: I would suggest that you contact the manufacturer of your wastegates first for direct replacement parts... I only offer my story here to show you that there are alternatives if "original" parts can't be found.

One other note: Tial wastegates, while they are the correct size and use an excellent Nomex diaphragm, have a small lip to seal the diaphragm into the housings. This "lip" or "bead" is unique to Tial and as such their diaphragms would not make good replacements for other brands.

- Cleaning up the internals

The internal parts of my wastegates were fairly easy to clean up. The remains of the diaphragm were easily scraped off the pressure cup and housing with a razor blade, and a good scrub with a firm brush removed most of the corrosion and remaining debris, followed by a wash and dry. The main focus in cleaning the internal parts is to remove anything that might hinder smooth movement or damage the new diaphragm. Even though the result still looks quite "dirty", all the internals are now smooth and clean to the touch. Special attention should be paid to the surfaces of the "bolt ring" on the upper and lower housings. This needs to be smooth and clean to ensure a proper seal, however you do not want this to be a polished smooth surface. A little bit of texture will ensure some "bite" to hold onto the diaphragm flange.

Cleaned internals:

- Checking and lubricating the exhaust valve and stem

The next item to check is the exhaust valve stem. This is the shaft that bolts to the bottom of the pressure cup and goes through the lower housing to pull up on the wastegate valve. The shaft should move freely up and down with very minimal side to side play. The exhaust valve should be free of any nicks or cracks, and should seal nicely into it's seat. If the valve or stem are badly damaged you should consider replacing the entire wastegate, however professional machining may solve the problem. I am not going to go into that process here.

Once you have checked that the valve stem moves freely and is in good condition it should be lubricated with high temperature anti-seize compound. Be sure to use the high temperature version (Zinc based) and not regular anti-seize (Copper based) as this part of the wastegate will be exposed to exhaust gases. Make sure the stem is completely coated in anti-seize and that it still moves freely.

- Reassembling the wastegate

Since I am sure you took careful notes when taking the wastegate apart ... reassembling it should be a breeze. The first step is to install the pressure cup into the new diaphragm.

For my setup I had to punch extra bolt holes into the diaphragm flange. A single hole paper punch worked perfectly, although it is a scary process. This also leaves two of the original holes unused and while this isn't ideal, I don't expect it to cause a problem. Just to be sure I did place the punched out "plugs" from my new holes into the unused holes to improve the seal. This step shouldn't be common for most installations, and is only mentioned here to explain where the extra holes came from in the future pictures.

Next reassemble the internals. In my wastegates there is a washer that goes on the valve stem first, followed by a round plate, then the cup and diaphragm combo, then another washer and finally a small nut. Since these nuts had worked loose previously, I choose to use a little thread-lock to keep them in place. You might want to consider using high temp thread-lock. I didn't myself, and when I re-open these in a few years time, I'll let you know how it held up.


Now for the trickiest step... putting the housing back together. For this you'll probably need a friend. Place the wastegate spring back into the cup followed by the top plate (in my case). The top housing then goes over the entire assembly. Here is the hard part... you must simultaneously compress the wastegate spring, and line up the diaphragm holes, and line up the bolt holes, and ensure that the diaphragm doesn't get pinched, AND then install the bolts to hold it closed. I found the easiest way to do this was to have a friend hold the housing closed while I lined up the diaphragm and bolt holes... then I quickly put in two bolts on opposite sides of the housing to hold it in place... only threaded in halfway. It took a couple attempts to get everything in the right place. I then threaded in the other 4 bolts and double checked that the diaphragm flange was sitting flat. Only then did I tighten all the bolts down to their final position.

The final step is to pressure test your wastegate so I will briefly cover that process. In a nutshell you will want to use a compressor to put air into the lower fitting on your wastegate to test that it opens and closes correctly. I would suggest starting at 5psi and slowly increasing the pressure until you see the exhaust valve open. Excess pressure (20? 30?) PSI should not be maintained for extended periods of time... only long enough to ensure everything is functioning properly. You can also check for pressure leaks by pressurizing (one at a time) the top and bottom chambers of the wastegate. The top chamber should hold pressure perfectly... the bottom chamber will loose a bit of pressure as some air escapes around the imperfect valve stem seal. This I expect is normal... although the pressure loss should not be excessive or rapid.

Also by testing the minimum pressure required to open your wastegate you can find out what strength your spring is. Springs come in a wide range of sizes (usually noted by the colour of the spring) and your manufacturer can provide you with stronger or weaker springs to adjust the wastegate to suit your application. The strength of the spring will set the minimum pressure at which it will open. Even with a boost controller, if you have a 10psi spring, you will always require a minimum 10psi of boost before the exhaust valve will open. The boost controller then uses pressure in the top chamber to hold the wastegate closed when it wants to boost higher than the spring minimum.

Thanks to Herman at Cherry Turbos for his input on this project and to everyone else who helped me gather information. I hope this helps someone out in their project. Before you go and rip your car apart please reread the disclaimer at the top of this page... if your car blows up, etc... it's not my fault . Good luck!

Contact info can be found at the bottom of my main page here:

The information on this page was put together by Steve Brecht 2003. If you use this page anywhere else please kindly ask my permission and keep my name somehow associated with it. There isn't anything too groundbreaking here but I'd still like to keep track of where it goes as it did take a fair amount of time to compile. Thanks.

Last updated: July 20, 2003