Heat Riser Stuck open? or closed?

[JimmyMac]

There is quite a lot of information in the Tech on cracked intakes resulting from stuck heat risers. However can someone tell me from these pics attached if mine is stuck open? or closed?. While exploring the source of a vacuum leak (13-14in) I got into looking for cracks in the manifold when I noticed that the heat riser is stuck , not surprised as it has sat for 13 yrs, however there isn't a bimetal spring attached to the opposite side of the counterweight. Since I live in the Bay Area in Nor CA the climate is fairly mild If this is stuck closed then I really dont have to worry about the excessive heat on the intake manifold and will just endure the longer warm up, however if it's stuck open then I would be more concerned, I just dont want to open that can of worms if I dont have to at this time. As you can see the manifold below the carb still looks good so I'm assuming that it may be closed but I dont know how long it was run like this either.

1970 FJ40 2bbl asian, stock, with vsv

 

[73FJ40]

Looks Open, but you decide..

I have a NOS heat riser assembly in my parts stash, and the riser plate (inside the exhaust manifold) is just about parallel with the flat side of the counterweight crescent. The riser plate is also just about perpendicular to the saw cut on the front end of the heat riser shaft, where the thermal coil spring would anchor.

If you look at the FSM illustration of the heat riser, it shows you the orientation of the heat riser plate both cold (straight up-and-down) and hot (at an angle, which looks like your situation). I've attached the picture for you to judge.

 

[JimmyMac]

Hey 73FJ40,

Just to clarify that when you say "open" you meant heat-off as deplicted in the right side diagram?
Anyway thanks for detailing out the position of the CWT and spring slot, that and the diagram explains a lot.

I think I will let sleeping dogs lie...no reason to mess with it right now.

I appreciate the help
JMc

 

[sggoat]

I have a '77 with a floppy riser. I think I have it positioned in the open position. there are no connections to it on either side. I think I am going to drill out the holes on either side of the exhaust and plug them(per FastEddy). Question--what difference does this make if it is there or not? Seems like an unrestricted exhaust would be best.
Anybody have the exhaust pressure specs for a 2f?

 

[Fast Eddy]

If it's floppy, the pressure is likely to push it open. If it's removed it will take longer to warm up than it would if it was repaired with a bimetallic spring. You won't notice any 'performance gains' with it removed.

 

[73FJ40]

Open = Hot Position

I suppose I was thinking cold = closed and hot = open, i.e., with the heat riser in the hot position (right illustration) no diversion of the exhaust gas up towards the bottom of the intake manifold.

I think the counterweight is positioned to twist the riser blade open (to the hot position), only resistance being the spring. With the spring weak due to corrosion, and the force of the exhaust gas heading out the exhaust pipe, the riser plate probably have no option but to fail and seize up in the 'Hot' position.

 

[JimmyMac]

Follow-up on heat riser open or closed and bolt size

I ended up taking off the manifolds to fix the vacuum leak and discovered that my riser is stuck differently than thought in the previous posts. I wanted to post a couple of pics to document what that position is relative to the counterweight. It appears that mine is stuck half way between open and closed, whether thats good or bad I dont know. The butterfly almost blocks most of the intake thereby preventing the usual intake cracking however its restricting the exhaust significantly as its blocking off half of the pipe.

My big question is what is the best way to handle this now? I want to keep the stock manifolds, so should I leave it as-is? unstick it and try and find a new bi-metal spring and housing (its gone)? or remove it and drill, tap and plug?

Another question is with the 3 heat riser bolts themselves, the one that is inserted thru the top by the block has a 14mm low height head but the other 2 towards the left fender has what appears to be 17/32 (.530) head. To big for a 13mm and to small for a 14mm ? I am almost certain that these are original...but maybe not...do they have 13.5mm wrenches?

Any insights?

 

[Fast Eddy]

Tough call. Common wisdom would be to remove it and tap and plug the holes. I'm pretty sure you won't notice any performance difference from your old tractor motor though. If you unstick it and get it working you're always going to have to worry about it getting stuck in a worse position later.

Are you sure the 13.5mm bolts aren't just rusted out 14mm bolts? I'll bet a 6 point 14mm socket will work fine on them.

 

[JimmyMac]

My first inclination is to remove and plug. My thinking is without the butterfly there is a more natural airflow and less resistance, also without any re-directed air to concentrate the heat load on the intake I shouldn't have to worry about the notorious cracking...does that sound sensible? is there more to this? has anyone experienced problems after removing the heat riser?

I tried the 6pt socket and its way loose, besides that only 1 bolt allows you to use a socket the other will not allow engagement so a box wrench seems to be the best way to go...see pic above...the bolt on the right .

pretty quirky....