A4 exhuast hot section rebuild

[68PearsonRenegade]

Hi folks,
As the title suggests I'm rebuilding the hot section of my late model A4. I dropped it into my Pearson renegade yesterday. I've perused westerbekes catalog and priced out the flange, I've also perused moyers. I've had wonderful experience ordering many items from Moyer and I thank them for their continued support of the A4 engine.
My question is, what is the advantage to back pressure fitting on the MMI flange? Also is black pipe construction of the hot section the most cost effective. My old hotsection appeared to no have the water entry section either?? Either that or it was corroded and fell off when I removed the system. What is the value of that? I guess I'm trying to wrap my head around the exhuast system and how it functions. My hot section goes to a wet exhuast.

[68PearsonRenegade]

Not sure why my pic posted sideways. But their she is. My late model being raised up for installation into the boat. Many Moyer parts on her

[Dave Neptune]

First are you raw water cooled or using an heat exchange?

In a raw water cooled engine the cooling water exits from the exhaust manifold to a anti-syphon valve then to the exhaust hot section, then the water and exhaust exit the boat.

With a heat exchanger the "raw water is circulated through one part of the HX" then to the exhaust as above. The coolant circulates through the engine then out the exhaust manifold to the HX (to give up it's heat to the cool raw water) then back to the engine.

Yes black pipe is most cost effective. There is also stainless steel available at McMaster Carr for a price. Both will need to be cobbled together and it is easiest to use the MMI water injection section available to avoid welding or brazing together a fitting.

Dave Neptune

[68PearsonRenegade]

Thanks Dave,
It is raw water cooled and it appears the old engine and exhuast system did not have an anti siphon valve installed. I suspect this is how water got into the old block and destroyed it over the winter. This what the hot section of my exhuast looks like. Its unclear to me where to me the anti siphon valve goes.
Thanks for your help.

[Dave Neptune]

That exhaust is a poor design! The injection point should be far below the "el with the injection nozzle" as water could easily get in during cranking.

The exhaust hot section should rise up a few more inches if possible and the injection point must be much lower. How much room do you have?

Dave Neptune

[68PearsonRenegade]

I have a few inches I could bring the hot section up and plenty of room to drop the injection section down, around 8 inches, the previous owner oddly piped the wet exhuast up to the injection section... instead of piping the hot section down to it. I'm starting to wrap my head around how this system works... I've attached a diagram for a rough idea of exhuast design. How does it look? And also also still scratching my head about where the anti siphon valve would go.. I'm guessing on the water injection point?

[Dave Neptune]

That would be good. You can move the Injection point up a bit, far less to wrap and cooler for the engine area.

Dave Neptune

[Dave Neptune]

That would be good. You can move the Injection point up a bit, far less to wrap and cooler for the engine area.

Dave Neptune

[msmith10]

The anti-siphon valve goes between the water exit point on the manifold and the injection point on the exhaust. You loop the hose up as high as you can and put the valve at the top of the loop.

[TimBSmith]

Some links from my riser replacement. Pearson 30 74

Here is a photo off a Pearson I salvaged. I think it depicts the original Pearson water injection fitting for a RWC engine.

https://photos.app.goo.gl/owJyXrBYReod6AN56

Here is an album I created from my project

https://photos.app.goo.gl/nhceKPQi3hjATfrL8

I put a lot of effort in cleaning up the exhaust manifold surface the where the flange gasket seats with the flange. I recovered the flange and the Moyer injector from the PO build. Paid a machinist some money to work some torch and torque magic beyond reach of my workbench.

There may be a Pearson diagram that demonstrates preferred lift above water line for boat with water lift muffler. I recall seeing something for the P30 not sure about your boat.

I did a lot of research on pipe sealant. The consensus is don't mess with dope, the black pipe will rust together, the threads don't need it, and you are not taking it apart after it has been in the boat for a season. That said, I used some high temp dope so that I could adjust the components once in place. I installed a very slightly loose, once I had the build in place I could get another quarter turn almost everywhere to improve flange alignment and seal. Best with the project.

[68PearsonRenegade]

Here is a photo off a Pearson I salvaged. I think it depicts the original Pearson water injection fitting for a RWC engine.

https://photos.app.goo.gl/owJyXrBYReod6AN56

Here is an album I created from my project

https://photos.app.goo.gl/nhceKPQi3hjATfrL8

I put a lot of effort in cleaning up the exhaust manifold surface the where the flange gasket seats with the flange. I recovered the flange and the Moyer injector from the PO build. Paid a machinist some money to work some torch and torque magic beyond reach of my workbench.

There may be a Pearson diagram that demonstrates preferred lift above water line for boat with water lift muffler. I recall seeing something for the P30 not sure about your boat.

I did a lot of research on pipe sealant. The consensus is don't mess with dope, the black pipe will rust together, the threads don't need it, and you are not taking it apart after it has been in the boat for a season. That said, I used some high temp dope so that I could adjust the components once in place. I installed a very slightly loose, once I had the build in place I could get another quarter turn almost everywhere to improve flange alignment and seal. Best with the project.

Thanks! those pictures are very helpful and thanks for the heads up. I'll have to do my research. I could salvage a few things off the old exhuast system but they are mediocre in shape so im just going to shell some money out to Moyer for a new injection point/ Flange.

[edwardc]

The anti-siphon valve goes between the water exit point on the manifold and the injection point on the exhaust. You loop the hose up as high as you can and put the valve at the top of the loop.

The anti-siphon valve must be located above the waterline in order to be effective.

[sastanley]

Thanks! those pictures are very helpful and thanks for the heads up. I'll have to do my research. I could salvage a few things off the old exhuast system but they are mediocre in shape so im just going to shell some money out to Moyer for a new injection point/ Flange.

I found that it usually takes a lot of soaking (Blaster/Kroil) and a vice to dismantle old exhaust sections. (or crushing and picking out bits from the salvageable parts.) I bought new ones from Moyer on the last rebuild, now I have one each of the manifold flange and the water injection nozzle, and can take my time rebuilding for the next replacement, and will have it ready for a quick swap out to minimize down time. Mine seem to last about 5 years when using black iron.

[68PearsonRenegade]

Behold Afourians, my new hot section featuring Moyer water inlet and flange. I opted to build my own siphon valve setup. Yes I had to visit three different stores to find the proper pipe fittings.

[Dave Neptune]

Looks very good indeed. One point though, loose the brass fitting as salt water will destroy it quickly. Use bronze, stainless or Marlon as they will hold up well in salt water.

That is a check valve in the "center" if not an anti-syphon Marlon loop works very well.

Dave Neptune