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Finding Type 4 TDC Without A Scale
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Amskeptic
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PostPosted: Mon Feb 23, 2004 4:02 pm    Post subject: Finding Type 4 TDC Without A Scale Reply with quote

This is apropos of a post that I accidently deleted.
The flywheel is provided with a hole that lines up exactly in the middle of that big round opening on the crankcase to the left of the center seam. There may be a rubber plug in the opening. You can redraw your TDC mark on the metal scale if the numbers have been obliterated, just sight up from your inside pulley rim notch. You can also check the accuracy of your flexi-plastic scale. ( mine was dead-on)
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ratwell
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PostPosted: Mon Feb 23, 2004 4:30 pm    Post subject: Reply with quote

This is a great trick as I was alluding to when I said aim the timing gun at something else but I think the mark you're looking at is just coincidence. You've obviously never seen an A/T in a bus from that location. The opening allows access to the driveplate bolts. Rotate the engine, unbolt, repeat.

The rolled pins in the back of the M/T flywheel that pass the TDC sensor on the other side are the calibration. You can't check the accuracy of the plastic scale but that's not really the point...

With the flywheel off you can align one of the roll pins with the sensor and make your mark on the flywheel that lines up with whatever mark your put on the case in the hole. That mark will be TDC so if your timing light can't retard to 7.5 BTDC (advance to 5 ATDC, whatever) you're going to need to adjust the mark (counting teeth for degrees etc) unless you want to eyeball calibrate your timing scale. You can set the engine to TDC #1 and do the same thing if it's already assembled but it's harder to paint the mark especially more than one (bracket the timing mark with a red mark 2 degree left, green mark 2 degree right). The point of marking the flywheel is that it's larger and you can fine tune the timing. The resolution on the scale is pitiful and you can't really check "dead on" by only one point of reference.

The plug is plastic and one of the three feet usually break off. Design by the same dufus who made the alternator adjustment cover.

Finding TDC is best done by testing the height of the piston accounting for rock and a quick check of the valves and or distributor rotor.
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edge540T
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PostPosted: Sat May 28, 2022 1:26 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

Amskeptic wrote:
This is apropos of a post that I accidently deleted.
The flywheel is provided with a hole that lines up exactly in the middle of that big round opening on the crankcase to the left of the center seam. There may be a rubber plug in the opening. You can redraw your TDC mark on the metal scale if the numbers have been obliterated, just sight up from your inside pulley rim notch. You can also check the accuracy of your flexi-plastic scale. ( mine was dead-on)
Colin

A few years later I totally agree, there are others marks on the flywheel but just face distribuitor on the mark to #1 and a hole apears right on the crankcase big opening, checked with a plastic stick on piston #1 spark plug hole.

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PMS means TDC in spanish, motor is CJ serial number with dual solex carburetors

Trying to find the sweet spot for timing idle seems around 4 to 5 btdc.
I wish to leave idle it to 0º to 2 atdc to not goes beyond 32º tdc on high rpm roof, but on low rpm and low acceleration hesitate a bit, like sudden pulls.
Otherwise idle higher than 6º means on high rpm roof achieves to 42º btdc and the feeling isn't good.

Seems my high rpm advance tends to go a bit too far, I don't know.


Last edited by edge540T on Sat May 28, 2022 1:29 am; edited 1 time in total
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PostPosted: Sat May 28, 2022 1:29 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

Really nice clear photos, gracias!
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busdaddy
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PostPosted: Sat May 28, 2022 8:39 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

I'm dying to know, what's going on with that thermostat and pulley arrangement there?
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PostPosted: Sat May 28, 2022 8:42 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

it will get you close but making a pair of line marks on the flywheel when the heads are off using a dial indicator and say .020" drop each way will get you a dead on measurement as defined as a pencil mark. Doing it with the heads on can be 2 or 3 degrees off, which is enough to cause problems if you are using stock timing. One must remember that there is an arc of maybe 5 to 7 degrees at TDC where the piston does not move. Being at one side of that is a lot of error.
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edge540T
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PostPosted: Sat May 28, 2022 9:21 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

busdaddy wrote:
I'm dying to know, what's going on with that thermostat and pulley arrangement there?
Just relocation out of the ground, it's a buggy.
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Wildthings
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PostPosted: Sat May 28, 2022 9:50 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

What distributor are you running? If its a DVDA then the retard can needs to work if you are using the book spec. The 28° BTDC spec is at 3800+ rpms with the hoses OFF.

Note that some 009 distributors have way too much advance and will cause boggy running if set at the 28° spec as the idle will be too far retarded.

If you have the motor on a stand, you can find TDC within a half degree or less by just using oil. Turn the engine on the stand until the 1-2 side cylinders are pointing upward and the turn the crank to get the #1 piston near TDC compression. Now fill the cylinder through the spark plug hole with clean oil, rocking the crank back and forth to home in on TDC when the oil will be the highest in the spark plug hole. Because of the difference in area between the area of the piston top and the cross sectional area of the spark plug hole a couple of thousandths up and down movement of the piston will be easily detected by and up/down movement of the oil in the spark plug hole.

If you put too much oil down into the cylinder having a syringe on hand to remove the excess can come in handy. You of course need to get rid of the majority of the oil in the cylinder before the engine is ever cranked. Just rotating the engine until the 1-2 cylinders are down will do this well.

This can be done with a fully dressed engine in situ, but takes more care and visibility is limited. On a buggy it would be easy enough though.
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PostPosted: Sat May 28, 2022 11:16 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

I find TDC on #1 by finding the valve overlap point on #3. It's easy and 100% foolproof. It wrks for all cylinders, the opposite will always be at TDC when its opposite is at overlap. Not sure this method is accurate to set your timing scale by but it's pretty accurate.

Valve overlap is obvious when the exhaust valve is just closing the intake is just opening. (could be vice-versa if you're turning the engine over the other way) The valves look like when you are twaddling your index and second finger on the table. On a Bus it's a little hard to see the #3 valves while also turning the engine, so a helper can help but single-handed you can do it too.
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edge540T
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PostPosted: Sun May 29, 2022 2:07 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

edge540T wrote:

Trying to find the sweet spot for timing idle seems around 4 to 5 btdc.
I wish to leave idle it to 0º to 2 atdc to not goes beyond 32º tdc on high rpm roof, but on low rpm and low acceleration hesitate a bit, like sudden pulls.
Otherwise idle higher than 6º means on high rpm roof achieves to 42º btdc and the feeling isn't good.

Seems my high rpm advance tends to go a bit too far, I don't know.


I think have found the sweet spot no matter what grades it have, idle 4-5º with this calibration is my bet.
I'm doing the test 4th gear and 40-45 km/h... and a gently acceleration in straight road.
Idle upper than 6º seems like a racing car and goes to 40ishº at max advance, but accelarates like a charm.
Idle lower than 3º hesitates in the firsts steeps of the gently acceleration but the whole feeling is good.
May it's a too hard test but let it me find the less bad advance I guess.

This is the distribuitor, the rotor is with rpm limiter but I think don't limit anything, can I change for fixed one? 009 is called?

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Wildthings
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PostPosted: Sun May 29, 2022 4:43 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

Having an ALL IN ADVANCE of 40° BTDC is right in spec. Best to set your timing at FULL MECHANICAL ADVANCE though and not to worry about what it reads at idle, for near sea level this would be 28° BTDC @ 3800rpm, hose(s) removed from the distributor and plugged.

ALL IN ADVANCE and FULL MECHANICAL ADVANCE are not the same, one is with the hose(s) on and one with the hose(s) off. Full mechanical advance replicates full throttle high rpm driving when you demand the most from your engine while all in advance replicates an almost coasting condition when your engine is doing little work at all.
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edge540T
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PostPosted: Fri Jun 03, 2022 4:15 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

This is a mine https://oldvolkshome.wetwesties.org/ovhignbo.htm

This is my distribuitor, not rpm limit kind.

Bus & Pickup Late 1976-1978 All States, 1979 Federal * 2000
Note: This Distributor also fits Type 4 (412) 1974
Distributor: VW 021-905-205P, Bosch 0231 168 005 > 022-905-205S, 0231 170 093
Note: 0231 170 093 dist primarily used on California Late 1976-1978 and all Federal 1979 Models
Can Use:
Points: 01 011
Condensor: 02 074
Rotor: 04 033
Note: 0231 168 005 dist originally equipped with Speed Limiting Rotor 04 016 (5400rpm)
Dust Cover: 039-905-241, Bosch 1230 500 139 > 1230 500 147
Cap: 03 010
Distributor Cap Clip: 034-905-265, Bosch 1231 251 033
Parts Kit (Shims, Washers & Hardware): 059-998-211, Bosch 1237 010 007
Coil: 00 012
Vacuum Can: 07 060
Ignition Wires: 09 171
Spark Plug: W8CC
Timing Set At:: 7.5deg BTDC @ 850-950 rpm (Man Trans), 900-1000 rpm (Auto Trans) w/strobe, vacuum hose connected
Advance/Retard Range: Vacuum: 8.5-11deg Adv @ 7.9 In. Hg; Centrifugal: 8-13deg @ 1600 rpm, 20.5-24.5 @ 3400 rpm


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Wildthings
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PostPosted: Fri Jun 03, 2022 9:24 am    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

The timing that is correct for your distributor and works well for you engine is:

FULL MECHANICAL ADVAMCE: 7.5° + 20.5° = 28° this is what you set your timing at at 3800 rpm, hoses off

Typical ALL IN ADVANCE: 28° + 11° = 39° this is just what you live with and mostly never have to worry about because you engine isn't doing much work when it occurs. 40° to 42° if fine as well.

You can add advance as you go up in elevation, typically 1° for every thousand feet above 4000'.
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Vanapplebomb
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PostPosted: Sat Jun 04, 2022 12:47 pm    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

edge540T wrote:
busdaddy wrote:
I'm dying to know, what's going on with that thermostat and pulley arrangement there?
Just relocation out of the ground, it's a buggy.


That’s for your cooling flaps Shocked Shocked Shocked Shocked

That is a really bad spot for that to be. There is not much heat on top the case, and I bet that closes partially when you drive at speed.

I’m not sure why you moved it. The stock location is higher than the bottom of your case. I have an off road buggy with a Type 4 engine that I beat the snot out of. I am in no way concerned about the location of the thermostat.

Get that thermostat back in the hot blast of air coming out of the bottom off the engine.

To make it analogous to a water cooled car… what you effectively have done is remove the thermo element of the thermostat in the radiator, and placed it in the engine bay… no hood. Needs to be in the coolant.
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edge540T
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PostPosted: Sat Jun 04, 2022 2:02 pm    Post subject: Re: Finding Type 4 TDC Without A Scale Reply with quote

Vanapplebomb wrote:
edge540T wrote:
busdaddy wrote:
I'm dying to know, what's going on with that thermostat and pulley arrangement there?
Just relocation out of the ground, it's a buggy.


That’s for your cooling flaps Shocked Shocked Shocked Shocked

That is a really bad spot for that to be. There is not much heat on top the case, and I bet that closes partially when you drive at speed.

I’m not sure why you moved it. The stock location is higher than the bottom of your case. I have an off road buggy with a Type 4 engine that I beat the snot out of. I am in no way concerned about the location of the thermostat.

Get that thermostat back in the hot blast of air coming out of the bottom off the engine.

To make it analogous to a water cooled car… what you effectively have done is remove the thermo element of the thermostat in the radiator, and placed it in the engine bay… no hood. Needs to be in the coolant.


It's a beetle one, was 65ºC? The original is 95ºC if I remember, it's working flawless with the temp gauge, opens and closes when it has to do it, the problem here is on cold days and a open motor like this one, it's a better place, it stays nearly closed to 15-25 minutes until reaches around 100ºC on the oil gauge, like so many things you can iterate solutions.... well check the restoration, vaccum and isopropil alcohol https://www.thesamba.com/vw/forum/viewtopic.php?p=9502321#9502321
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