advance timing causing high CHT

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VWinVT
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Location: Northeast Kingdom Vermont
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advance timing causing high CHT

Post by VWinVT » Tue Jul 22, 2014 4:05 pm

Hi,
I posted this question in the type 2 forum with no response, so i'll try it here., I have only owned my 81 Westy (California) for a little over a year. We really love it and want to enjoy for many years to come. Thus, I installed a DD CHT gauge. As to be expected, I was running hot. I adjusted the AFM, following the "how-to" post here to richen the mixture a bit to cool the motor. It worked well and solved my stalling at idle issue, I was way lean. Anyway, I now run at about 410* cruising at +/-55mph.
I decided to check the timing, and found it to be set at 10* ATDC at idle. I have also discovered that the dizzy on my van is from the 83-84 watercooled. I set my timing with hose off and idle stabilizer plug into itself to 28* BTDC at +/- 3500rpm. I eagerly went for a ride, only to discover my head temps rose to 445* at +/-55mph! I tried to readjust the AFM, but went as rich as I could go with no improvement. After a lot of trying different timings and AFM settings, I am right back to where I started from...timing set to 10*ATDC at idle (hose connected) and running a bit rich.
Why does my engine run hotter, the more I advance my timing?

Thanks for you help,
Bob

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Amskeptic
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Re: advance timing causing high CHT

Post by Amskeptic » Tue Jul 22, 2014 9:02 pm

VWinVT wrote: I am right back to where I started from...timing set to 10*ATDC at idle (hose connected) and running a bit rich. Why does my engine run hotter, the more I advance my timing?
It is a nasty "hockey stick graph", a quadratic exponential trip into hell when you advance the timing.

Consider this:
The piston is travelling up the cylinder on the compression stroke, heating the air rapidly as it compresses.

Should you decide to ignite the fuel/air mixture up at the plug a bit too soon during the compression stroke, an even more rapid heat/ pressure wave from the burning fuel/air descends and collides with the compression stroke. Once it reaches "spontaneous combustion temperature", the entire charge of fuel/air just explodes instead of a nice steady progressing flame front. This is called "pinging" or "knocking".

Duh, you say, I am not talking about that.
Right, I reply, but the above hockey stick graph is still working its magic at tamer advance.

You cannot feel the effects of over-advance in its milder forms, but the engine senses it as a little "trying to run the engine backwards" inefficiency - low power and ridiculous heat as the combustion charge wastes its energy on trying to push the piston and crankshaft backwards.

1) Is your vacuum hose running to an advance unit or a retard unit?
If you have the timing set to 10* ATDC currently, which way does the mark jump when you pull off the hose at idle?

2) Does your idle stabilizer stabilize the idle by changing the timing?

3) How is the overall power when the timing is at 10* ATDC and the head temps are acceptable?
How is the power when the timing is at 28*/3,500rpm and the head temps skyrocket? Better or worse than the above?

Get rid of stupid variables like a twisted scale on the fan housing. The upper "leg" should be perfectly horizontal and do not let the screw twist it as you secure it. That can distort your timing readings.

Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

VWinVT
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Re: advance timing causing high CHT

Post by VWinVT » Wed Jul 23, 2014 5:09 am

Well, it appears that I have been timing the motor using the wrong mark. The PO painted a notch and that is what I have been trying to use. The notch that the PO painted/made is CW of the correct mark (it appears to be matched up with the 0 (zero) stamped on the fan, resulting in the timing being a 90* hockey stick!! Thus, the 10*ATDC was actually 15*BTDC at idle...I can't believe the motor didn't explode when I timed it to 7.5 BTDC at idle with the wrong mark. :cherry: I have measure the 42mm from the bolt, opposite the notch on the fan and lo and behold...the factory notch! In this process I have tracked down a few vacuum leaks and am awaiting arrival of a new S boot; when it arrives (tomorrow) i'll time the motor using the factory mark.

VWinVT
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Re: advance timing causing high CHT

Post by VWinVT » Wed Jul 23, 2014 7:39 am

methinks the fan/pulley is/are from a Porsche and the PO misidentified the timing mark...i.e. used the Porsche mark, not the VW mark...

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Re: advance timing causing high CHT

Post by Amskeptic » Wed Jul 23, 2014 10:20 am

VWinVT wrote:methinks the fan/pulley is/are from a Porsche and the PO misidentified the timing mark...i.e. used the Porsche mark, not the VW mark...
Too much guesswork, confusion, supposition.

The bus type 4 engine has a NOTCH on the forward pulley half to line up with a scale.

The 411/412 type 4 engine has a viewing port in the fan housing with a "0" mark and a 28* mark stamped onto the aluminum of the fan itself.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

VWinVT
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Re: advance timing causing high CHT

Post by VWinVT » Wed Jul 23, 2014 11:43 am

Image


Well, here it is; my pulley and fan set-up. I have it sorted out now. In the lower left portion of the photo, you can see the white paint dot. This corresponds with the notch that the PO and I have been using to try to time the motor. CCW from this mark, you will see a small piece of duct tape indicating the location of the factory timing mark that measures 42mm (+/- 1 5/8 inches) CW from the bolt seen behind the belt opposite the 'key' in the fan.

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Re: advance timing causing high CHT

Post by Amskeptic » Wed Jul 23, 2014 9:46 pm

VWinVT wrote:Image


Well, here it is; my pulley and fan set-up.
In the lower left portion of the photo, you can see the white paint dot.
This corresponds with the notch that the PO and I have been using to try to time the motor.
CCW from this mark, you will see a small piece of duct tape indicating the location of the factory timing mark that measures 42mm (+/- 1 5/8 inches) CW from the bolt seen behind the belt opposite the 'key' in the fan.
I am getting lost! In the lower left, I see a green dot.

The 411/412 marks on the aluminum of the fan are located at the exact top of the fan at #1 TDC.
AT THIS POSITION, the bus/vanagon notch on the pulley is several degrees to the left (about 11:00 if it were a clock dial) because the SCALE has a "0" that is at about 11:00 if you had a scale.
Do you have a scale? You need a scale. While I am yammering about making sure your scale is not twisted, you apparently don't have a scale.
Colin

Image
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

VWinVT
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Location: Northeast Kingdom Vermont
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Re: advance timing causing high CHT

Post by VWinVT » Thu Jul 24, 2014 4:43 am

I guess I still need to know left from right! I meant lower right on the pulley is the white dot/notch that the PO made that was used to improperly time the motor. I do have a timing scale and screen. I removed them temporarily to gain better access to the fan/pulley. I read ratwell piece on locating the timing mark, and it was right where he said it would be, unfortunately l, it was not the make that had been used to time the motor. My new S boot arrives today (old one had a split) and I will time the motor properly.

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Amskeptic
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Re: advance timing causing high CHT

Post by Amskeptic » Thu Jul 24, 2014 9:14 am

VWinVT wrote:I do have a timing scale and screen. I removed them temporarily to gain better access to the fan/pulley.
Well then, I need to settle down. Vanagons are pretty tight back there, and I like to paint my customers' pulleys with highlights on the "0" and "180" for valve adjustments and on the 28* on the scales to help us time them. Good luck! Let us know how it works.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

VWinVT
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Location: Northeast Kingdom Vermont
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Re: advance timing causing high CHT

Post by VWinVT » Thu Jul 24, 2014 9:37 am

Good timing! I am.sitting in my van and I have it properly timed to 30* BTDC all wound up. I am ama,ed at how smooth it runs now, the power is solid and steady. As I sit here, my idle temp 350*. I drove for about 30 minutes. I cruised comfortably at 55mph and pretty much stayed there...never did that before! Into a solid headwind on rolling terrain, it hovered between 415 and 420...never over 420. I would like it to run cooler, but as Randy in Maine told me.once, "there is nothing hotter than you on the road"!!

VWinVT
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Re: advance timing causing high CHT

Post by VWinVT » Thu Jul 24, 2014 12:04 pm

Just went for another run up Lowell Mtn. in Lowell VT. steepest longest hill around and it topped out at 428* in 3rd gear going 35. Last week it got up to 444*. VERY windy today and general cruising is a 2 hands on the wheel event...+/-45mph saw temps around 410*. It smells to be running a bit rich. I will continue to seek out vacuum leaks...Oh, the damn timing gun I bought last week...it stopped working! there's $30 ill never get back!

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Re: advance timing causing high CHT

Post by Amskeptic » Sat Jul 26, 2014 12:26 am

VWinVT wrote:Just went for another run up Lowell Mtn. in Lowell VT. steepest longest hill around and it topped out at 428* in 3rd gear going 35. Last week it got up to 444*. VERY windy today and general cruising is a 2 hands on the wheel event...+/-45mph saw temps around 410*. It smells to be running a bit rich. I will continue to seek out vacuum leaks...Oh, the damn timing gun I bought last week...it stopped working! there's $30 ill never get back!
"I have it properly timed to 30* BTDC"
Who SAID 30* was "proper? Where do these numbers crop up? The scale itself has a rectangular notch from 25-28* to cover scatter, and that is not 30*. The manuals suggest an advance of 21 to be added to the usual 7.5 static starting spot with a new distributor, but as they get older we take the timing from the idle to make sure that 28* max is max.
Retard the timing to 28* MAX MAX MAX and shoot for 26* at 3,400 rpm just to see if it helps reduce temps.

Experiment with an unplugged ox sensor and richen the mixture screw one turn clockwise, just to see if it helps. If it does not, restore to original settings.
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

VWinVT
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Location: Northeast Kingdom Vermont
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Re: advance timing causing high CHT

Post by VWinVT » Sat Jul 26, 2014 4:38 am

Ok, I'll reset timing to 26*, hopefully that cheap gun I bought will cooperate. I unplugged the O2 once before and it ran SUPER RICH, wouldn't I want to lean the mixture after uplugging?

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Amskeptic
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Re: advance timing causing high CHT

Post by Amskeptic » Sat Jul 26, 2014 8:21 am

VWinVT wrote:Ok, I'll reset timing to 26*, hopefully that cheap gun I bought will cooperate. I unplugged the O2 once before and it ran SUPER RICH, wouldn't I want to lean the mixture after uplugging?
If it runs super rich with the 02 sensor disconnected, it means that the AFM is set super rich. WE have control over the AFM, whereas the ECU takes control with the 02 sensor. Are you comfortable with adjusting the AFM?
Colin
BobD - 78 Bus . . . 112,730 miles
Chloe - 70 bus . . . 217,593 miles
Naranja - 77 Westy . . . 142,970 miles
Pluck - 1973 Squareback . . . . . . 55,600 miles
Alexus - 91 Lexus LS400 . . . 96,675 miles

VWinVT
Getting Hooked!
Location: Northeast Kingdom Vermont
Status: Offline

Re: advance timing causing high CHT

Post by VWinVT » Sat Jul 26, 2014 10:12 am

Yes, I have been adjusting it during this timing adventure. But, I have been doing it with the O2 plugged in. I read your 'how to' and have been using it as my reference. I have backed up the timing and am headed out for a drive.

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