How are yall fixing onan intake manifolds?

[RED-Z06 2,221]

Im getting ready to tear down a P218G to do valve lash and swap to a non-pumper carb.  The carb is off my blown P220G, i was cleaning it up and was doing my standard intake leak test and to my surprise..it failed, big leak im assuming is from the harsh pressurization from the bad seat.  It effortlessly split in half. Its cleaned up..but, do i drill out the old tabs and bolt them in? Use "the right stuff"?

[lynnmor 7,305]

I drill them thru and use stainless screws, washers and locknuts, I don't trust tapping the weak aluminum.  Motoseal 1 is used for a sealant.

[kpinnc 12,005]

I use a silicone gasket maker on the seam. Only on the outside of the body.

 

 

[lynnmor 7,305]

Click on this, then click on the link in post #1.  While I do things slightly different, the thread can be helpful.

[RED-Z06 2,221]

Man ive read so many different walk throughs on this, its hard to believe all the onans i have and have had this is the first one to fail. 

 

So, here is my plan..and ive ordered the stuff to do it.

 

Motoseal1 is pretty much universally lauded as the sealer to use.im going to drill the top half to 5mm and use a 4mm drill tap on the bottom half, this should let me use stainless allen head 4mm screws..if this doesn't pan out I have 4mm nuts on hand.

 

Plan is to apply the MS1 and let it flash to begin curing, then install the carb to hold the center in place.  Then install the 4mm allen screws from the center out..then put nuts/bolts through the ends to hold them..then let it sit 24hrs.

 

Im hoping the M4 threads hold, like the write up above says..they really dont have to be tight...just snug.  

[lynnmor 7,305]

Sounds like a good plan.  I prefer thru screws, you will see why when you tap that thin cast aluminum.  

[RED-Z06 2,221]

14 minutes ago, lynnmor said:

Sounds like a good plan.  I prefer thru screws, you will see why when you tap that thin cast aluminum.  

Its definitely small stuff, cant figure out how it wad held from the factory..like a spot weld 

[lynnmor 7,305]

11 hours ago, RED-Z06 said:

Its definitely small stuff, cant figure out how it wad held from the factory..like a spot weld 

One casting has holes and the opposite side had lumps.  When assembled, the lumps went thru the holes and were peened like a rivet.

[RED-Z06 2,221]

3 hours ago, lynnmor said:

One casting has holes and the opposite side had lumps.  When assembled, the lumps went thru the holes and were peened like a rivet.

Gotcha, so i should be able to knock the "heads" off and expose the holes.

[lynnmor 7,305]

1 hour ago, RED-Z06 said:

Gotcha, so i should be able to knock the "heads" off and expose the holes.

There are holes in the riveted side, the other side is solid aluminum.  If you can knock of some of the riveted material then hole location might be better determined.  I just drill thru both sides and temporarily put a bolt in.  Do one hole at a time to keep things aligned.  When all holes are done, take it apart, clean and reassemble.

[RED-Z06 2,221]

Waiting on motoseal now.  I ended up using the drill tap bit to drill through the top far enough to pilot the bottom, then drill/tapped the bottom separately.  The plan to use the 5mm bit to drill the top probably would have worked but what i ended up doing was using the 4mm drill tap to "strip" the upper holes which ended up a snug roughly 4.2mm fit on the m4 bolts.  They all threaded in by hand..not going to crank them down until i have the motoseal in.

[RED-Z06 2,221]

To update this 10mos later, it did work, i ran nuts on the back of each screw as added security, ran like a top and still runs like a top today.

[kpinnc 12,005]

1 hour ago, RED-Z06 said:

To update this 10mos later, it did work, i ran nuts on the back of each screw as added security, ran like a top and still runs like a top today.

 

My 520-H had the common "surging/ hunting" throttle and need to run at more than half choke to smooth out. Carb cleaning and valve adjustment made no difference. As soon as I sealed the manifold, she smoothed out and needed no choke after starting. 

[Horse Newbie 7,069]

I don’t know if a P218G has heat shields over the exhaust or not…

but I learned on here, and discovered that on my 1994 520-H, on the P220, the heat shields were rubbing on the intake manifold, and had rubbed “notches”

I think it was @lynnmor who mentioned this and got me looking. I am not sure mine had rubbed enough to rub all the way through, but I went ahead and sealed the joint between the upper and lower halves.

I had it all apart anyways. I had surging going on, and I don’t know whether sealing the intake or a new Chicon carb fixed the surging but it surges no more.

Oh, and I did use the Motoseal 1 …

Edited March 3 by Horse Newbie

[RED-Z06 2,221]

23 minutes ago, Horse Newbie said:

I don’t know if a P218G has heat shields over the exhaust or not…

but I learned on here, and discovered that on my 1994 520-H, on the P220, the heat shields were rubbing on the intake manifold, and had rubbed “notches”

I think it was @lynnmor who mentioned this and got me looking. I am not sure mine had rubbed enough to rub all the way through, but I went ahead and sealed the joint between the upper and lower halves.

I had it all apart anyways. I had surging going on, and I don’t know whether sealing the intake or a new Chicon carb fixed the surging but it surges no more.

Oh, and I did use the Motoseal 1 …

To my knowledge every P series should have the full heat shield set around the exhaust 

[lynnmor 7,305]

7 hours ago, RED-Z06 said:

To my knowledge every P series should have the full heat shield set around the exhaust 

Yes, and most eat into the intake manifold so some metal needs to be removed where they touch.

[Horse Newbie 7,069]

On 3/3/2024 at 4:19 AM, lynnmor said:

Yes, and most eat into the intake manifold so some metal needs to be removed where they touch.

Did the metal trimming on the shields to “Nip it in the Bud”.

[Bill D 1,919]

Has anyone tried Reinzosil for sealing one of these manifolds?  Looks like an interesting product.