'64 Corvair Turbo not "hitting boost"

[bbodie52]

Your 1964 engine should be fitted with a harmonic balancer. If you are going to confirm the timing setting, you should also verify the accuracy of the timing mark on the harmonic balancer. The outer ring can sometimes slip and can be inaccurate.

...Harmonic balancer outer rings can slip and provide bad info. Distributors can have bad/stuck advance mechanisms...

Harmonic balancers are three-piece assemblies with a cast inner mount attached to the crankshaft, an outer steel ring, and the two are a press fit with a rubber insert that holds the two metal components together. As the harmonic balancer ages the press fit between the two metal components can begin to loosen, and the outer ring can slip. This could mean that the outer ring would no longer be in proper alignment with the center part, which is held in place on the crankshaft with a Woodruff key. With a solid crankshaft pulley the Woodruff key ensures proper positioning of the timing mark on the outer edge of the pulley. But with a faulty harmonic balancer the outer mark can slip, which can mean your timing mark may no longer be accurate.

The Corvair shop manual indicates that there should be a registration mark on the face of the harmonic balancer that indicates a proper relationship between the inner hub and outer ring. If the mark is there but the two parts are not in alignment, the harmonic balancer has slipped and is failing and must be replaced.





You can read more about harmonic balancer slippage at the following Corvair Center link...

http://corvaircenter.com/phorum/read.ph ... 740,494964

[miniman82]

It would help to have pictures of the engine, to clear up any confusion. As stated the turbo impeller is not as free to spin as a modern one, due to the fact that Corvair units have what's called a positive (aka carbon faced) compressor seal. This puts drag on the the rotating parts, as the seal is in constant contact with them. There are also differences in the bearings, the Corvair uses a single journal bearing and runs at relatively low speed. Modern turbos have double floating journal bearings, and their speed can easily be twice what a Corvair's turbo might see.

As long as you can easily spin the impeller with your finger and it's not making any noises like it's rubbing on something internally, it's most likely fine. Only other things that might lead to a no-boost situation are exhaust leaks or fuel/ignition problems. Make sure you have a pressure retard unit not vac advance, and make sure it actually works by applying some shop air to it so you can verify that it moves. Many of the original units are now dead, which will cause massive detonation in the engine on boost. Make sure the engine is getting enough fuel, either by installing a wideband O2 meter or going to a rolling road and have them snake the tailpipe.

Once you have done all of this, you should have boost. If not, there may still be a turbo problem and you should send it my way. I have seen a couple units which for whatever reason had tight bearings, which is why I like using 'seasoned' bearings in rebuilds vice new ones. They tend to have a tad more clearance, which is a good thing for Corvair people who tend to run thicker oils. It's also possible for the carbon seal to be bound up a little, placing too much drag on the shaft- usually the cause is worn out o-rings in the seal not allowing it to move.

[VincentLuong24]

Thanks for the replies! I'll be sure to check all of this an keep you guys posted. I am currently waiting for my pressure retard to come in and as soon as it does, I'll check the harmonic balancer, set the timing to stock and see if I can hit boost.

[66CorsaConv]

Hey Turbo Guy? Long ago when I ran a Superflow air flow bench the development engineers asked me to do a Water Intrusion test. My bench had 7 220V industrial vacuum motors in it. Water wasn't going to be a good idea.

So I grabbed a Craftsman Shop Vac. Turns out it can suck/blow almost 100 CFM at a couple inches of mercury pressure drop.

I wonder if using a shop vac to drive the exhaust side would be a way to test a turbo boost capacity off the car?

Just wondering. Other ideas include green food color and clear tubing from a hardware store and a yard-stick.

Home made manometers. If they don't find you handsome, they might as well fiond you handy.

[Scott V]

So I grabbed a Craftsman Shop Vac. Turns out it can suck/blow almost 100 CFM at a couple inches of mercury pressure drop.

I wonder if using a shop vac to drive the exhaust side would be a way to test a turbo boost capacity off the car?

did you measure that it could blow almost 100 cfm @ a couple inchs of mercury? i can see it sucking that - surpriseing it will blow that.

it dont see how you could test the turbo boost capacity off the car w/a shop vac. the exhaust side gets hot exhaust gas to spool the turbo. its heat & volume of the gas that makes the turbo work. youd need a real big shop vac to get enough air to spool a turbo. easier to use a gas or elect motor to spin the turbo if you wanted to test it.

-Scott V.

[66CorsaConv]

I had measured the suction flow but what goes in must come out. The idea I had was to use the suction of the shopvac on the turbo outlet toward the muffler. Exhaust out.

The expansion of the exhaust across the turbo and the mass flow are the primary mechanisms. Lots of Thermodynamics here. The heat may effect the bearing drag.

The idea is with what ever the real flow is it would be nearly constant at a repeatable pressure drop. Even 80 CFM is about 2000 rpm Wide Open for a 2.6L 164 Cu In engine.

If the shop vac can not make it spin, there is probably something wrong. If you had multiple turbos, you could measure the back pressure on the plugged off outlet to the cyl head intake port. Air/Fuel Out.

Spinning it with a high speed portible drill is a good idea too. Can you get enough rpm?

The turbo with the highest static boost is the healthiest. Both the compressor and expansion side are working best.

Just a Shade Tree Mechanic idea.

[Scott V]

I had measured the suction flow but what goes in must come out.

yup - flow wise but not pressure wise. youd get the 100 cfm out but i dont think youll get the couple inchs of mercury out when blowing in the turbo exhaust.

The heat may effect the bearing drag.

not enough to affect your tests.

If the shop vac can not make it spin, there is probably something wrong.

agree - & its the shop vac doesnt have enough flow & pressure to drive the exhaust side of the turbo.

Spinning it with a high speed portible drill is a good idea too. Can you get enough rpm?.

the turbo spins around 80k - 100+k rpm @ full boost. i think youd want to spin it 40k or better to get any boost. when i suggested a gas or elect motor to spin the turbo for testing i was thinking youd have to drive it w/a step up gear or belt system to get the rpm. youd need a few hp motor to do this.

-Scott V.

[miniman82]

The heat may effect the bearing drag.

They spin a whole lot easier when up to temperature, hot oil makes a big difference.

[VincentLuong24]

So I fixed the timing, replaced the VA to a PR, check to make sure the boost gauge is working and checked the turbo for "free spinning". All checked out well and I am still not making positive pressure. I guess I got to go back and check for exhaust leaks again.

[Grandpacorvair]

Wondering is there was any resolution to this problem..?

I was reading the First post and there is a mention of "removing mufflers" as a test...."MUFFLERS"? Last time I checked my Spyder it had one muffler....

A typo or has someone done some creative engineering that might be causing the boost issues....

Kerry

[miniman82]

Are you sure the pressure gauge is working? These engines don't make much stock boost, but they do make quite a bit of vacuum. It's possible you have a pinhold in the plastic tube going up to the dash, so the pressure is escaping. Check with a modern boost gauge and/or run a new line to verify. If it's still confirmed to not be making boost, it's time to pull the turbo and tear it down. My guess? Carbon. The hot side is probably gunked up so while it may still move, it's not free enough to spin up to boost speed. I rebuild turbos at low cost for forum members, so if that ends up being the problem drop me a line.