The Stovebolt Site Forums The Shop Area Engine Shop Heat riser question

Well things are really shaping up, got it running good and starting to look pretty good too. Should be on the road in a couple weeks. My question today is with the heat riser. I bought a new spring from Chevy Duty and put it on. The valve rotates very freely, no hangups anywhere. My question is how hot does the darn thing have to get to open? I ran for 20 minutes and it is still closed, I got my torch out and put a some direct flame to it and it opened right up. Problem is it closed again in about a minute even with the engine still running, by this time for about 25 minutes and was good and hot. Sounds to me like my spring in not good or should it be even hotter to open?

your spring may need to be under less tension when it is installed

In the 57 manual it says sthe spring should only be turned 1/2 turn from where it rests when it's not hooked on. Sorry, my spring off to and am getting one from chevy duty, or I could help more.

I only have it less than a half turn for the tension setting. :confused:

hmmmm....Why would you want your heat riser to open when the engine gets hot? I would think you would want it to close.

You sure you got the spring mounted correctly? The heat riser deflects exhaust to the underside of the intake. Spring is supposed to dampen the baffle's movement during operation. Im unsure how much the spring actually 'moves' the riser, like the spring choke in a carb. I'd think that as RPM increased, the exhaust gas flow would press the riser baffle more open, with the spring trying to force it shut. But you don't want it to close more when it gets hot, cuz that could boil the gas in the carb & cause vapor lock or other strange performance probs.
You sure you didn't take the temper out of the spring with that torch? Make sure the riser is not stuck, and the counterweight is intact and in the right position when you install the spring. Does the riser move when you revv the engine?

good luck

chip

Well I hope I didn't ruin it with the torch, I didn't fry it, just put heat on it to see if it actually moved. It does stay shut at idle and bounces around when it revs up, maybe this is how it is supposed to work, I'm not sure. It does move very easy so I don't think it is stuck at all. When it is shut it blows some exhaust out the hole for the heat riser on the cam side and makes it sound like crap. I took the spring off and it falls open and my exhaust leak is almost unnoticable. I've read some people don't use the heat riser and others say it is a must. What are your thoughts Chip?
Thanks

Hmm I dunno, each situation is different. I live in the deep south, where it doesnt get very cold. The heat riser didn't do much for me, but you may need it if you drive in colder weather. My riser was stuck, so when I had the exhaust manifold off, I cut it out with a grinder. Then I drilled and tapped the riser holes, and plugged them with 2 short bolts.
The intake and exhaust manifolds do bolt together, so Id imagine some heat transfer happens anyway. Now for the aftermarket fenton setup, exhaust or water heat is a must.
In your case, Id prolly put the spring on and run it like it is. Unless the exhaust leak can be heard over all the other noise while you're going down the road.

These old machines made so much darn racket when new. My import-driving buddies think my ride is going to blow apart at any second. (And thats before my 235 started knocking)

Chip

Well it does get cold here darn it but its not my daily driver so it won't see much cold weather. I don't think the leak could be heard over the rest of the noise the darned old thing makes as you pointed out but at idle it sure sounds bad. I'm going to try running without it and maybe plug up the holes as you did if it runs out OK. I have a set up fentons I'm thinking about putting on or I may have Kansas Kustoms convert my manifold to a split one. Looks like they do good work has anyone used them? If I went this route I would have to worry about heating the manifold as it use the stock method. Thanks again for all the good advice. Sorry I'm such a pain on stupid things like a heat riser but I've never encountered them before.
http://www.inliners.org/Advertisers/kkk_ad1.html

If you drive at all in the winter here in Kansas, you need the heat riser. I ran my 216 for the first winter without one, the truck was a terrible runner until it warmed up and I had to choke the devil out of it.

As for split manifolds, it's tough to go wrong with cast Fentons or the Kansas Kustoms. I have looked at the KK work, and they do an excellent job, plus you get to use the heat riser. The shaft hole can be bushed.

Yea it sure as heck gets cold here and I don't like it. I like the KK solution because of the heat riser but I already own the fentons. Although they need blasting and a good coating on them, plus I have to get the water plummed to the intake so it could be a push in cost if I just sold them and paid KK. Just another decision to make this winter. Thanks again for all the suggestions. At least my heater does work good in the old beast.
Bruce

Whatcha reckon guys ,, GM spent a whole bunch of research time and money deciding that the engine worked best at certain temperatures , and having the intake charge operating within a given temperature range . So they made a manifold heat riser device .
If the heat riser is stuck open then the engine will get too hot a fuel charge once the engine is warmed up , this can cause various performance faults , eg. detonation , pinking , lean running .
If it is stuck closed the fuel mix is not heated and poor cold running performance is experienced , excessive use of the choke is needed , etc ,etc .
The manifold heat riser on my truck has 2 springs on it , one is much shorter than the other ( less coils, and wound the oposite way ) These 2 springs oppose each other and stop the riser rattling , The longest spring does all the work of opening or closing the riser valve and works fine , the engine performs fine all year round .
There is probably a bit in your truck manual showing how to set it all up , there is in mine .

Yes--In my view this whole thread has been inaccurate and backwards. The heat riser should be open(directing exhaust gas to the floor of the intake) when the engine is cool and closed when the engine reaches operating temperature. Removing the heatriser flapper in a hot weather environment would result in a situation where the intake is perpetually heated--I wouldn't recommend that in the south or really anywhere else--gonna cause poor performance. My dos pesos from hot Texas.

You guys are all wrong on what Heat riser is for.
First it is closed when cold. It blocks the exhaust from going out the pipe more and redirects it to the intake to warm that up and the carb with it. Then, as it warms up the coil gets warmer and the riser opens slowly to unblock the exhaust and run it clear thru with no blockage. By then the intake and carb should be warm enough to run correctly. Yes, in cold weather w/out it, it takes a long time to warm up. It does NOT change the choking or such on star-up, but may need to run on partial choke longer before warming. The riser does not "flap" around while running, it's closed or open.

Open / Closed ........ depends on your point of reference ....... sure .

When the exhaust is directed to heat the base if the intake manifold , the flap is closed to the exh. ... or ... open to the manifold ........... same action .
When the exhaust is not directed to heat the manifold , the flap is open to the exhaust ... or .. closed to the manifold ...........
Clear as mud , eh .

Well sure is a lot of good advice here, thanks for all of it. From what I have learned here mine is not working correctly. It is directing the exhaust (open or closed depending on your take) to the intake at all times. It never opens up, however it does bounce around once warmed up. It directs to the intake until it gets good and hot then it bounce open and shut with throttle applid. I'm thinking this is not correct. It runs great while cold then has a hesitation when warmed up. I checked the timing over and over,same with the points, has new plugs r-45's, new plug wires, new fuel pump, new card. I think I'm going to take if off and see how it does. If it runs fine when warm then I'll try another new one. Maybe I fried it with the torch when I was testing it.

I'm with you, Willib. Same setup on my 216, same result. Installed a new spring (mine from Jim Carter) following the photos and steps in the shop manual. Tested it with a heat gun... worked great, but when the engine is run, it doesn't gather enough heat to rotate the flapper. I don't know if I should be concerned or not. Engine runs fine but I don't take it out in cold weather...no heater.

I finally got round to scanning the pic in the manual ,, sorry you have to stand on yer left ear to view it , LOL .
the album is http://picturetrail.com/dusty2790

[img]http://pic4.picturetrail.com:80/VOL50/482254/1357959/15837979.jpg[/img]