Timing mark mystery, Please help me solve Options

[bbrock]

Cleaned up the impeller on the 2.0 liter today and need to repaint the timing mark. To my surprise, I found two marks to choose from (IMG:style_emoticons/default/new_shocked.gif) The mark on the right (nearest TDC) was cut with a file and is exactly 52.5mm from the center of the "0" for TDC. According to Haynes, that is the correct distance for 27 degrees BTDC. The farther mark looks to be original and is about 57.25mm from TDC. If Haynes and my math are correct, that would be around 29ish degrees BTDC.



Now I have a vague memory of cutting a mark on an impeller of one of the five Type 4 engines I've worked on, but too much alcohol has swashed through my brain in the 35+ years since that event could have happen to remember why. I can think of two reason: the original had a broken fin and I stole this one from a bus engine, or I just put a mark in where Haynes said it should be, assuming the other was wrong.

What really bothers me is this image from another thread has a pic with 27 BTDC marked exactly where my original mark is not at 52.5mm where Haynes says it should be, but TDC in that pic is not where mine is using the impeller blades as a guide. So can anyone help me figure out which frickin' mark is the right one? Is Haynes wrong? If it is the one I cut, any idea why the other one is there? Did buses have a different mark? So confused. (IMG:style_emoticons/default/confused24.gif)

(IMG:http://www.914world.com/bbs2/uploads/post-8384-1196294703.jpg)

[jmalone]

You will want to re-balance that fan unless you indexed it so that it can be assembled again exactly as it was.

[bbrock]

You will want to re-balance that fan unless you indexed it so that it can be assembled again exactly as it was.

I did. At least I did something right (IMG:style_emoticons/default/beerchug.gif)

[bbrock]

I found the timing mark template on The Bird and am feeling more confident the mark that was filed in is correct, but WTF was that other mark from?

[bbrock]

Either folks were busy with the holidays, or I actually managed to stump the chumps (IMG:style_emoticons/default/laugh.gif) Let's try turning this around. Assuming the 27 degree mark on my impeller is the original, and the 29 degree mark was added, can anyone think of a reason to have that mark on a carb converted car? The only way I would have added that mark is if I read a tech tip somewhere and I had a very bad habit of rushing to implement every little tip I read back in my youth.

[Olympic 914]

If you have another fan handy can you compare the location of the 0 TDC mark ? I don't know bus motors but if the fan housing had the notch in a different spot the TDC and 27 deg mark would be correspondingly different. (IMG:style_emoticons/default/confused24.gif)

[Valy]

Ljet and Djet have different timing marks. The fan probably came from a different engine. That's why you have different markings.

[914_teener]

You will want to re-balance that fan unless you indexed it so that it can be assembled again exactly as it was.

I did. At least I did something right (IMG:style_emoticons/default/beerchug.gif)

How was it done?

[bbrock]

You will want to re-balance that fan unless you indexed it so that it can be assembled again exactly as it was.

I did. At least I did something right (IMG:style_emoticons/default/beerchug.gif)

How was it done?

I have corresponding marks notched in the pulley ring that correspond with the timing marks so the pulley can be put back on in the same position it came off. I don't know if the D-shaped washers are used in addition to the weight crimped into the pulley for balancing but all of mine are the same size and thickness so I'm assuming equal weight. I wouldn't mind having the balance rechecked before putting it on the engine though. Would most machine shops be able to do this?

[bbrock]

If you have another fan handy can you compare the location of the 0 TDC mark ? I don't know bus motors but if the fan housing had the notch in a different spot the TDC and 27 deg mark would be correspondingly different. (IMG:style_emoticons/default/confused24.gif)

I had forgotten about it but yes, I do. Next time I'm out by the storage shed, I'll take a look.

Ljet and Djet have different timing marks. The fan probably came from a different engine. That's why you have different markings.

This seems most likely. What's weird is that I've had 3 1.7L engines from 914s with D-Jet, 1 2.0L 914 with D-Jet, and a 1.8 engine from a '74 Bus. The bus engine is chief suspect for a donor fan but I think that bus was originally carburetor and they didn't start using L-Jet until '75. Maybe that is wrong and my bus was originally L-Jet. I don't know much about buses other than I loved mine. Did they maybe start switching to L-Jet in late MY 74? Or maybe someone had already swapped fans on any of the other engines before I got them.

Sounds like one thing I should do is verify that the TDC mark on this fan is actually TDC.

[MarkV]

I would think top dead center would be the same on all type 4 engines. Those marks don't serve much purpose if you have a timing light with an advance meter. I guess you could use them to verify that the timing light is accurate. The only useful second mark is the one you use at 180 from TDC for setting the valves. Maybe someone made that mark to set total advance. (IMG:style_emoticons/default/confused24.gif)

[Valy]

https://www.thesamba.com/vw/forum/viewtopic.php?t=699839

[914_teener]

You will want to re-balance that fan unless you indexed it so that it can be assembled again exactly as it was.

I did. At least I did something right (IMG:style_emoticons/default/beerchug.gif)

How was it done?

I have corresponding marks notched in the pulley ring that correspond with the timing marks so the pulley can be put back on in the same position it came off. I don't know if the D-shaped washers are used in addition to the weight crimped into the pulley for balancing but all of mine are the same size and thickness so I'm assuming equal weight. I wouldn't mind having the balance rechecked before putting it on the engine though. Would most machine shops be able to do this?

The weight is used to balance it.

DO NOT drill out or machine any of the fan to balance it unless you want shards of of a fan in your housing. Seen it happen.

I'd have it dynamically balanced by a competent shop.

[bbrock]

Thanks for that link! I think we may be getting somewhere. First, that thread confirms that my TDC "0" mark is right where it should be. I think the clue to the second mark is in the last paragraph of the second to last post where they say to just set total advance (as @MarkV suggested might be the case) at 32ish degrees.

Thirty-five years ago I rebuilt the bottom end of this engine with a reground carb cam to convert to dueal carbs with a 050 dizzy. I'm pretty sure I'm the one who filed the second mark in and it probably was to add a mark for setting timing with the full mechanical advance dizzy. I'm guessing I read some instructions to set a few degrees more advance than stock and thought I'd be clever and file a mark to make that easy. I'm not sure why I put it at 29 rather than 32 but at least it fits with the idea of compensating for lack of vacuum advance. The project stalled for several decades and now I'm finishing the job and scratching my head trying to figure out what the heck I did. (IMG:style_emoticons/default/huh.gif) To add to the confusion, I did such a nice job filing in that mark that couldn't tell which is factory. I'm also leaning toward not using the 050 because I'd rather have vacuum advance. So my cleverness may have caused confusion with no good reason. That sounds about normal for me. (IMG:style_emoticons/default/screwy.gif)

[bbrock]

The weight is used to balance it.

DO NOT drill out or machine any of the fan to balance it unless you want shards of of a fan in your housing. Seen it happen.

I'd have it dynamically balanced by a competent shop.

But what qualifies as a "competent shop" for this? A competent machine shop or does it need to be someone who knows these engines? The latter might be hard to find around here.

[914_teener]

The weight is used to balance it.

DO NOT drill out or machine any of the fan to balance it unless you want shards of of a fan in your housing. Seen it happen.

I'd have it dynamically balanced by a competent shop.

But what qualifies as a "competent shop" for this? A competent machine shop or does it need to be someone who knows these engines? The latter might be hard to find around here.

If you put the fan back together the way it was and the weight is still there then you are probably ok.

As far as competancy, there are shops that just do fan and pulley balancing. There are lots here ...not sure about Montana.

I.m an engineer so any mass spinning at 5k rpm should be balanced.

But that's my OCD.

I have seen a couple of fans on T4 motors come apart because they machined metal away from the fan on the metal lip. This caused it to crack and come apart.

[stugray]

I just use the 0deg (TDC) mark on the flywheel and a variable timing light.
Its even easier to see than looking in the fan housing.

https://youtu.be/QtPd5qzyTk8

[IronHillRestorations]

I've made timing marks on the back of the flywheel that are seen through the plug in the back of the case. In my case the impeller was known to be correct, and I just indexed it with the stock timing mark, and used the appropriate transfer punch through the hole in the case to mark the flywheel.

I also made marks for TDC and BDC for valve adjustments.