Hi All

Under my carb or thereabouts, I believe I have what is called a heat riser. It has a coil spring at one end and a compression spring at the other end of the manifold. I don't know what it looks like in the mainfold but I think its a flap who's job was to allow heat up the intake manifold. Mine looks like it has been seized for the last 20 years. Is there anything I can do to get this to work again? Or is it even worth taking the risk of breaking something?

If its indeed stuck open will I be running with too much heat to the carb?

Oops sorry - its a 115 2 litre engine. Exhaust and intake manifold on the same side.

Oreo

Yes, this is the famous manifold butterfly valve that will roast your carbs if the valve jams and puts constant full heat upward. I dont think anybody has ever actually seen one that is fully functional. What most people do is pull their carbs and hit the butterfly valve with a hammer to set it at the best position.

Hi DD

Problem is the flap is in the exhaust manifold and they seem to be bolted together with the intake manifold at the flap. Only way to get there seems to be to take both manifolds off and seperate the two. I haven't had roasted carbs yet, what are the symptoms of an open heat riser?

Oreo

Allegedly, this is one of the causes of carburetor sections warping - like on the 3 piece pancake stack zenith carbs. I dont know how you can determine the position of the butterfly valve. And it may not be critical if the car has had no carb problems.

Oreo, how many miles are on the car and has it ever been taken off the road for extended periods when the valve might have seized forcing air upward?

DD

That's a good question - let's see 25 yrs old at a conservative 15K kms a year - about 350-400K kms. I have no idea if it was ever sitting for a period of time. What's I'll probaly do is spray some penetrant at the valve shaft for a while and see if it frees up. Will probably have a lot of smoke when it heats up though! If it doesn't I'll let sleeping dogs lie. Its not affecting my carb performance but I do have a nagging hot start problem which I thought might be linked to this.

Oreo

Oreo:

Mine is an M180 engine, so the schematic view in my mind may differ from the correct one for your engine. But the cause/effect relationship is the same. Too much manifold heat will both warp your carb, and also give you fits on hot-day hot starts. As to setting the heat valve for a permanent "off" position, my manifold heat valve is pushed by the exhaust gasses toward a normally open position, and the bi-metallic thermo-spring/counterweight arrangement works against this action to close it when cold. Therefore, I would guess that if you rotate the valve spring or counterweight so that the weight appears to lift or the spring seems to unwind and relax, up and toward the block on my car, this will rotate the inner flap to a closed postion that prevents excess heat to the base of the carb. Fix it solidly in this position for permanent off. Corrosion friction on the shaft will usually do this for you. Down side is a grouchy motor when you are warming it up, may tend to stumble a bit without carb heat but will settle down OK after engine temps are normal. You might check a Haynes/Chilton manual. They usually have good cross-section views of the engine which can lead you to the correct understanding of how your engine is configured.

for what it's worth...

230/8

Follow this thread and send CTH an email as he offers.

M130 Heat Riser Install Question

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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Oreo, I had the same problem. Both weights were 'down', therefore lettiing heat rise to the carbs all the time.
If you look at the parts catalog diagram, when the weights are 'down', the heat riser is open.
So I used 14" Channel lock pliers and penetrant to turn the weights 'up' 90 degrees (towards the valve cover). This keeps the risers closed all the time.
The car is very cold-blooded on startup, and I have to feather the gas pedal as the engines warms up, or it will stall.

Better than warped carb plates, though.

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1970 280S M130 engine- good runner
1971 250 M130 engine- #2 rod bearing, gone
1971 280SE (blown engine,parts car)
1977 German 280S W116-only 33 years old

Hello,
On the M115, the heat riser is much further away from th carb(that is mounted on rubber isolator anyway) and does not have counterweights. It could be stuck anywhere on your cars manifold
You would have to remove both the intake and exhaust manifolds, then seperate the two to see where the flap is at. A lot of trouble to go thru for something that may not make any difference to your *hot restart* difficulty.
There is an unauthorised modification that will give good HOT restarting, it will outrage all the environmentalist the world over, but your car will be an instantaneous starter all the time, hot , cold and anything in between
On the earliest 175CDS/CDTs there was a vent stack with a rod operated ventilation of the float chamber vapors, only open at or near idle to the atmosphere, so vapors escaped with the throttle at idle posotion, closing off at any position higher than idle.
Remove the complete choke housing and punch out the little metal cap that seals the *vent* area. It is the cap above the two small oval holes on the right(driver's) side of the carb housing itself and sealed off by the choke housing gasket. You could epoxy some mesh over the hole if you are concerned about debris getting into the carb float chamber, but I never bothered
I have not had any hot start or idling problems at all, even the hottest days are not a bother, just crank and it starts, slight stumbling for a second or so and then it's fine and never had the idle decaying in traffic jams whereas I have seen W124/W201 FI cars wilt in the extremely hot and humid weather, blow clouds of black smoke and eventually stall and refuse to restart :p
Have a good weekend.

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Nachi11744

Isn't it possible to run the car to operating temperature and then feel the carbs? Mine seem to be cool to the touch on the 220S when running. Even though one of the flaps rotates freely.

Also, why can't these things be maintained to run correctly? There is an instruction in the manual to lube the hinges of the heat shields with something called caramba IIRC. Probably never got done after the warranty period and they all froze up years ago.

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63 220S W111
76 300D W115
2013 VW JSW TDI M6

previously-
73 280 SEL 4.5
86 300E 5 speed
2010 VW Jetta TDI M6

Hello,
The later carb engines that did not make it to the USA, namely the M115 and M123 in the W123 both have sintered ceramic bearings that do not need lubrication. Both engines have single carbs, 175CDT on M115 and 4A1 on M123. The only *cure* for the stuck heat riser is a NEW exhaust manifold, trying to bash the stuck shaft out to change the bearings cracks the cast iron manifold. Bear in mind that the right hand drive engines have radically different manifolds from left hand drive plus the M115 manifold from a W115, which is a large diameter single outlet pipe swept forward, will not fit a W123, which uses a swept back single or dual outlet pipe.
It is not an ideal solution, but I still suggest removing the thin metal cap that seals off the external vent area on the 175CDT. IIRC, the W124/201 carb engines(M102)have an electrical external vent valve.
The dual carb sixes like the M180, M114, M108,M130 seem to run fine with the heat risers stuck closed, though if stuck open, the carbs do get very hot and there are cases where I have seen severe warping.
The 175CDT is a single piece casting, so it can take a lot more abuse from heat cycling without warping, at most, the rubber isolator bows or cracks or the bakelite heat insulator cracks. My W115's carb base flange is almost always cool to the touch with the engine running, with beads of condensation appearing after running at high revs for a few miles.
Hope that helps.
Have a good week.

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Nachi11744

Hi All

I managed to get my hands on the repair CD and looked at the page on heat riser. There is a repair kit with sintered bearing for it and it shows how to take the bearings off. But it doesn't show the inside and how it works. But looking at the diagram it seems that mine is stuck in the open position as my little stop flap is up. I'm assuming closed is when it is resting on the stop tab. I don't want to crack my manifold doing this so I going about this as carefully as I can. Maybe strip the shaft bare and get some penetrant on it.

My hot start is not a big bother but I do have to floor the pedal and crank about 5 seconds. This is in the owners manual, I understand. Its got a rich mixture from evaporated fuel in the manifold. I can smell it coming out the rear. Nachi - I'm going to pass on your advice this time as I don't want to modify the carb too much but its interesting to know.

From the advice given, my conclusion is although this is nice to have working, its not crucial. I'll have to walk away from it if it proves too stubborn or risk unnecessary damage.

Oreo

Hi All

I managed to get my hands on the repair CD and looked at the page on heat riser. There is a repair kit with sintered bearing for it and it shows how to take the bearings off. But it doesn't show the inside and how it works. But looking at the diagram it seems that mine is stuck in the open position as my little stop flap is up. I'm assuming closed is when it is resting on the stop tab. I don't want to crack my manifold doing this so I going about this as carefully as I can. Maybe strip the shaft bare and get some penetrant on it.

My hot start is not a big bother but I do have to floor the pedal and crank about 5 seconds. This is in the owners manual, I understand. Its got a rich mixture from evaporated fuel in the manifold. I can smell it coming out the rear. Nachi - I'm going to pass on your advice this time as I don't want to modify the carb too much but its interesting to know.

From the advice given, my conclusion is although this is nice to have working, its not crucial. I'll have to walk away from it if it proves too stubborn or risk unnecessary damage.

BTW - does anyone know if theirs is still working??

Oreo

From the advice given, my conclusion is although this is nice to have working, its not crucial. I'll have to walk away from it if it proves too stubborn or risk unnecessary damage.

If it ain't broken, don't fix it

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Nachi11744

Nachi

You know the mentality of a DIYer. Everything must work! And it very hard to just walk away from a job.....

Oreo