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Engine rebuild - No Start / No compression
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PostPosted: Sat Nov 18, 2023 3:51 am    Post subject: Engine rebuild - No Start / No compression Reply with quote

I am new to the world of the air cooled flat four. And since starting my journey to rebuild an old engine I have learnt a lot from reading many posts.

Now I have come to the point where a need some help. I am sure I have over looked something "obvious" in my engine build, but can't see it.

I started with a 1600 dual port engine, which I completely stripped down. I had the case line bored and machined to accept 92mm barrels. I have rebuilt the engine to an 1835cc with a W110 Engle cam and twin carbs (stock everything else).
I painted the tin, now it looks great, BUT, it wont start ....

I done the classic tests of spark, fuel and compression.
The spark is good. I have confirmed on all cylinders that when the piston is at the top of its stoke and both values are closed I get a spark.
The fuel is good. I get plenty of fuel through the twin carbs.

BUT I have almost no compression. ... I thought this might be caused by a leak in the value seats or a leak where the barrels make contact to the head. So I had the heads completely reconditioned and fly cut to give 9:1 compression ratio. I put the engine back together but no still no compression.

I then took the rockers off and performed a compression test and got 100 PSI!

So I assumed the problem is something to do with the rockers or the valve timing is out. I split the case again, to be sure I had correctly installed the cam. The one dot on the cam falls perfectly between the two dots on the crank.

So I put everything back together but still there is next to no compression with the rockers installed and solid compression with the rockers not installed.

I have reset all the valve clearances to .006' . I have completely disassembled the rockers (which are the original stock rockers) and I have cleaned every part and made sure the arms move freely but that made no difference.
I still only get compression when the rockers are off.

Any ideas on what I might have missed would be greatly appreciated.
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PostPosted: Sat Nov 18, 2023 8:22 am    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

[email protected] wrote:

I then took the rockers off and performed a compression test and got 100 PSI!

Any ideas on what I might have missed would be greatly appreciated.

If the valves were all closed (like when you had the rockers off), you'd measure some compression.

Post pictures of your rocker arms/pushrods as installed.

I'm in Arizona and don't fly, so I can't just come over and look.
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PostPosted: Sat Nov 18, 2023 9:10 am    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Quote:
Post pictures of your rocker arms/pushrods as installed.

What cusser said. Pictures really help diagnose issues in cases like this.

To me, based on your description, you have the valve timing events incorrectly set. Or the pushrods are too long based on the flycut heads.

If the engine is out of the vehicle, you can pull the #1 sparkplug and look to see if the piston is at TDC when setting your valve clearances.
At TDC the #1 intake and exhaust valve rockers will gently wiggle when the clearances are correctly set. If one is tight, your valve timing events are incorrect and need to be corrected.
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PostPosted: Sat Nov 18, 2023 11:05 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Thanks for the quick responses .. I was in Arizona last year. I was in Vegas for work and did a short road trip from Vegas to Page to Monument Valley and back to Vegas via Flagstaff and Kingman. Great trip Very Happy

I have taken pictures of the cylinder 1 and 2 rockers going full cycle of the engine, i.e. pictures have been taken at TDC and BDC for each cylinder in the firing sequence 1, 4, 3, 2 ... I have included a table just in case the pictures get out of sequence.
The piston is at the top of its stroke when both values are closed.

The rocker arms are loose enough for me to wiggle them when the valves are closed and I can spin the push rods.

At the moment I am in a body-off state, so I can work freely on the engine.

The beast
Image may have been reduced in size. Click image to view fullscreen.


Valve position table
Image may have been reduced in size. Click image to view fullscreen.


TDC #1
Image may have been reduced in size. Click image to view fullscreen.

BDC #4
Image may have been reduced in size. Click image to view fullscreen.

TDC #3
Image may have been reduced in size. Click image to view fullscreen.

BDC #2
Image may have been reduced in size. Click image to view fullscreen.
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PostPosted: Sat Nov 18, 2023 11:38 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Your valves look like they are not adjusted. Did you adjust the valve lash to .006 on both intake and exhaust, at TDC for each cylinder?
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PostPosted: Sun Nov 19, 2023 1:53 am    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Yes, both intake and exhaust are at .006. I guess that’s tough to see in the photos.
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PostPosted: Sun Nov 19, 2023 5:59 am    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

#3 does not look right. Is it the angle? Nevermind, I thought he was showing each pic at TDC. Got a little confused.
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PostPosted: Sun Nov 19, 2023 9:14 am    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

[email protected] wrote:
Yes, both intake and exhaust are at .006. I guess that’s tough to see in the photos.


Yes it is, because the valves are not adjusted right.

On the #1 photo, if the valves had been adjusted correctly, the exhaust on the #2 cylinder should be completely compressed, but it is not. So…. either you have the numbering wrong, or took a picture of the wrong side. I am guessing it is neither and that you have misadjusted the valves.

How about taking several steps backwards and take a picture of the engine? I can label it for you so you know where each cylinder is.

How are you finding TDC for each of the cylinders?
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TDCTDI wrote:
Basically, a whole bunch of fuckery to achieve a look.


67rustavenger wrote:
GFY's Xevin and VW_Jimbo! Smile
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PostPosted: Sun Nov 19, 2023 9:29 am    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Sun Nov 19, 2023 11:24 am    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

To me, BDC#4 is what TDC#1 should look like.
Are you sure the dots on the cam gears are lined up?
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PostPosted: Sun Nov 19, 2023 11:34 am    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Should probably get rid of the BDC all together in order to avoid confusion.
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PostPosted: Sun Nov 19, 2023 1:23 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

You have this photo labeled as BDC #4:
Image may have been reduced in size. Click image to view fullscreen.

That is the RIGHT side of the engine, thereby showing cylinders 2 (at left) and 1. You can read the cylinder # "2" stamped into the engine tin above. You can also see the upward hump of the heater box's front air outlet in background, indicating that the camera is aiming frontwards.

Unrelated to your non-start situation: Do you have the metal plates to cover the preheat outlets on your muffler? You won't need the preheat outlets with your dual carbs. If you don't have such plates, you can either order them from a VW supplier, or make your own. I have a few photos in my gallery of how to make them using a metal "mending plate" from a hardware store. If interested, indicate here and I'll post them in another response.
Image may have been reduced in size. Click image to view fullscreen.

Las Vegas via Flagstaff and Kingman? Good going- you were hopefully on a short section of historic Route 66. How did that desert landscape compare to what you've seen in your country?
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PostPosted: Sun Nov 19, 2023 5:58 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Rome wrote:
You have this photo labeled as BDC #4:
Image may have been reduced in size. Click image to view fullscreen.


This is what #1 TDC looks like.
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PostPosted: Sun Nov 19, 2023 7:29 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Are you sure the cam is correctly indexed to the cam gear? It's an easy mistake to make. There are three possible positions and only one is correct!
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PostPosted: Mon Nov 20, 2023 12:36 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

I tend to agree that it is most likely the cam indexing … looks like I’ll be doing a complete tear down again … I’ll let you know how it goes
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PostPosted: Mon Nov 20, 2023 2:47 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

What the rockers look like at the end of each stroke is hard to judge. Try this...
    Add a TDC and BDC mark to your crank pulley. The TDC mark applies to both #1 and #3 cylinders. When the BDC mark lines up with the case split the #2 and #4 cylinders are actually at the top of their stroke.
    Start with cylinder #1 (closest to right front wheel). Rotate the crank pulley CW while you watch the #1 valves. You are looking for valve "motion" not just open/closed state. It is easier to rotate the crank if you remove all the spark plugs. Keep rotating the pulley until you start to see the #1 intake valve start to open (start of intake stroke). The crank pulley should be near TDC as the valve opens (intake valve actually opens just before TDC), and near BDC as the intake valve closes (end of intake stroke).
    Over the next 360deg of crank rotation both valves should be closed (compression & power stroke).
    Near BDC at the end of the power stroke the exhaust valve should start to open and remain open over about 180deg of crank rotation (exhaust stroke). At the end of the exhaust stroke the TDC mark should line up with the case split and the exhaust valve should be closed (end of exhaust stroke). If you continue to rotate you should see the intake valve start to open as you restart the 4-stroke cycle once more.

Repeat this for each cylinder confirming the valves are opening and closing at approximately the correct time. There is valve overlap which means valves may open slightly before you expect and remain open longer than you expect. This is fine. You are just making sure the valves are opening around the correct timing and not 90deg off from expected.


One other thing... how have you set your ignition timing to start the engine? Set your points to 0.016" and static time your ignition to 7BTDC. This is good enough to get the engine running.
To get the engine running, spray some starting fluid down both carbs.
Have you confirmed you are getting spark at the spark plug WHILE cranking the engine? Static testing the coil by hand rotating the engine is good, but checking for spark while cranking is the only way to know what happens while the starter is pulley huge current away from the battery and ignition coil. Bad wiring can reduce the current that makes it to the ignition coil while crankingl resulting in the coil not sparking while the engine is cranking.
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PostPosted: Mon Nov 20, 2023 3:51 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Ashman, it is super simple stuff. There is no reason to check each cylinder, to find out. The timing sequence and events of an ignition cycle happen in a sequential preset. One event after the next, one cylinder after the next. Super simple stuff. If you can set an engine up to #1 TDC, you can check a few basic things and set the distributor almost on the button! It is not rocket science.

In this case, based off of the OPs postings he is either confused which cylinder is which or he has assembled the engine together wrong. Again, sorry to use this so much, but when I was a mechanic I saw a lot of wrong. People would ASSume they could take an operating component apart and replace or rebuild it. It is not that simple, especially if you do not know anything. Which is what is going on here.

So, we finally figured out the engine may be misconstructed, as seemed pretty apparent reviewing the pictures, but there is always that doubt. So let’s see what they have going on. Let’s ask a few more questions, then point him in the correct direction.
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TDCTDI wrote:
Basically, a whole bunch of fuckery to achieve a look.


67rustavenger wrote:
GFY's Xevin and VW_Jimbo! Smile


Last edited by VW_Jimbo on Mon Nov 20, 2023 4:01 pm; edited 1 time in total
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PostPosted: Mon Nov 20, 2023 3:55 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

To the OP:

Set that crankshaft pulley up to TDC. Pop the valve covers and take a picture of the crank pulley and the valves. IF THE #2 exhaust valve (the rear most valve on the right side of the car) is not starting to open, turn the crankshaft another 360 degrees. Then check that #2 exhaust valve. If you cannot see it, like in the picture, you can feel it. The exhaust and intake valves on the front or #1 piston will be loose. .006 loose! The intake valve on the #2 cylinder will be the same looseness. But the exhaust will be being pushed by the rocker arm so there will be no free play.

What do you have? Pictures please.
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There is never enough time to do it right the first time, but all the time necessary the second time!

TDCTDI wrote:
Basically, a whole bunch of fuckery to achieve a look.


67rustavenger wrote:
GFY's Xevin and VW_Jimbo! Smile
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PostPosted: Mon Nov 20, 2023 4:20 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Remember what he first posted:

[email protected] wrote:
I am new to the world of the air cooled flat four.



[email protected] wrote:
I split the case again, to be sure I had correctly installed the cam. The one dot on the cam falls perfectly between the two dots on the crank.


Considering the above, my bet is that the valve adjustments and/or cylinder assignments are off.
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PostPosted: Mon Nov 20, 2023 5:38 pm    Post subject: Re: Engine rebuild - No Start / No compression Reply with quote

Cusser wrote:
Remember what he first posted:

[email protected] wrote:
I am new to the world of the air cooled flat four.



[email protected] wrote:
I split the case again, to be sure I had correctly installed the cam. The one dot on the cam falls perfectly between the two dots on the crank.


Considering the above, my bet is that the valve adjustments and/or cylinder assignments are off.


Exactly!
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Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

TDCTDI wrote:
Basically, a whole bunch of fuckery to achieve a look.


67rustavenger wrote:
GFY's Xevin and VW_Jimbo! Smile
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