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-   -   B400 - rocker adjustment (http://www.bristolcars.info/forums/6-cyl-bristol-cars/1648-b400-rocker-adjustment.html)

Bela 05-06-19 05:44 AM

B400 - rocker adjustment
 
The time will come when the rockers have to be adjusted.
The engine is equipped to my knowledge with a B 403 camshaft.
Would that make a difference?

Geoff Dowdle 05-06-19 07:41 AM

Bela ,
The standard valve clearance for
400 - 403(A engine) is .002 inch cold Inlet & Exhaust
late 403(AB2 engine) - 406 is .005 inch cold " "

But very few engines now have standard factory cams . Most have either
been re ground to another specification or the cam replaced and the clearance of these could be different from original standard cam .

Do you know the valve timing of the engine .
Inlet opening & closing , Exhaust opening and closing to try to identify which cam is fitted.

Geoff

Bela 05-06-19 05:23 PM

Quote:

Originally Posted by Geoff Dowdle (Post 9730)
Bela ,
The standard valve clearance for
400 - 403(A engine) is .002 inch cold Inlet & Exhaust
late 403(AB2 engine) - 406 is .005 inch cold " "

But very few engines now have standard factory cams . Most have either
been re ground to another specification or the cam replaced and the clearance of these could be different from original standard cam .

Do you know the valve timing of the engine .
Inlet opening & closing , Exhaust opening and closing to try to identify which cam is fitted.

Geoff

Thanks Geoff

I only found a notice of a PO that a 403 camshaft had been fitted. As you mentioned there are two options - early and late. I guess less clearance will
end in troubles.

I don't know the valve timing and I don't know how to generate that data. In the files there is a drawing. I will look for it.

Bela 06-06-19 10:04 PM

2 Attachment(s)
Quote:

Originally Posted by Bela (Post 9733)
In the files there is a drawing. I will look for it.

Here comes the drawing- for better reading twice. But I don't know the context of this drawing. I hope it was generated after purchasing a new camshaft.

Geoff Dowdle 07-06-19 01:27 AM

Bela ,

although the scan is quite clear to view , the information is not written in a form to express the valve timing correctly.

But after trying to sort out the information ,my comments are as follows (assuming a 403 camshaft is fitted or camshaft ground to 403 spec )

Inlet lobe lift of .180 inch (should be .205)
Exhaust lobe lift .200 (should be .205)
So possibly a worn camshaft or reground to a completely different grind.

Timing Inlet opening 34 BTDC
Inlet closing 44 ABTC
give duration 34 + 44+ 180 = 258 degrees (close to early 403 of 260 deg)

But the original standard early 403 timing is 15 BTDC - 65 ABDC ,
So it looks like if the timing is set as per those notes and the camshaft is a 403 cam or 403 grind , it is set about 19 deg too far advanced. Probably one tooth .
But these notes could have been taken during initial assembly (how accurately is unknown) & was corrected before final assembly .

Do you have a TDC mark on the front pulley or damper with a pointer ???
If so , set the number 1 inlet valve clearance at .002 cold, turn engine over until the clearance just closes (when you can no longer move the rocker sideways) and measure the distance between the pointer and TDC mark . Then calculate the approx opening of the inlet valve.
This ,although not an accurate measurement , will still show if the valve timing is set too far in advance or they adjusted it on assembly.

I hope this helps
Geoff

Bela 07-06-19 05:41 AM

Hello Geoff,

thanks for your comment and advice.

In the meantime I found a notice of a PO in the files that it is a late 403 camshaft. I hope I'll find more e.g. a bill.

Therefore I've to aks if I shall measure with 0,002 or 0,005 clearance or both.

Geoff Dowdle 07-06-19 06:18 AM

Bela ,
If the camshaft is a late 403/404/405 grind the advertised timing is
Inlet opening 36 BTDC
Inlet Closing 76 ABDC
Duration 292 deg (this is further away from the 258 deg of the notes.)
Lobe lift .205 inch
Recommended valve clearance .005 cold

I suggest you adjust the valve clearance firstly at .002 inch and rotate engine until you can not push the rocker sideways , as per my earlier post.
Then repeat at .005 inch clearance

--------------------------------------------------
The hand written notes could have been of the original badly worn camshaft before the engine was stripped for a rebuild.

Geoff

Bela 07-06-19 06:39 AM

My grandchild will spent the holidays with us so it will take time.

Bela 22-06-19 07:53 PM

1 Attachment(s)
Next week I will have a look.

In the meantime I found something in the WSM that sounds strange to me - see picture.

It is the first time I saw a cold clearance is minor than the clearance of a hot engine. How does it work? Parts expand when getting hot.

Bela 03-09-19 04:58 PM

The week was long - illness and other failed cars needed time too.

Result: 50 BTDC and 65 ABDC (measured under not optimized conditions with 0,005 clearance) are probably an evidence of the late 403 camshaft (36/76) and not a 401 or early 403 camshaft (15/65). Together with the written note of a preowner I'm sure enough to go on with 0,005 inch valve clearance. I hope the 0,0025 I'd found didn't harm the camshaft.

Thanks Geoff for the advice.

Geoff Dowdle 04-09-19 04:01 AM

Bela,
I suggest you recheck the inlet opening .

At 50 BTDC and closing 64 ABDC it gives a 295 deg duration .
50 BTDC seems excessively advanced or the camshaft sprocket is one tooth advanced on the timing chain .
295 deg duration is more than most sports/racing camshafts, an unlikely fitment for a 400.

I suggest you recheck at .005 clearance cold and also at .002 cold .
Are you sure the TDC mark is accurate ?
Are there 360 deg marks on the crank pulley ?
or how did you read the 50 & 64 ??

Is it possible can you advise the centre line of the inlet lobe .
That is the point of max lift of the lobe . You really need a dial indicator on the valve and read the degrees say a .020 before and .020 after the max lift point. The centre point between those two readings is the accurate centre line. Most standard Bristol cams have a centreline of 110 deg ATDC.
Some aftermarket cams are between 105 - 108 ATDC.

Many well worn engines with worn sprockets and chains run at 113 - 115 deg centreline which is effectively retarded and will lack performance.

Geoff

Bela 04-09-19 06:20 AM

1 Attachment(s)
Thank you Geoff

I don't have a dial indicator.


I'd checked with 0,002 and with 0,005.

0,002" -> 60 BTDC and 70 ABDC
0,005" -> 50 BTDC and 65 ABDC

I'll repeat. I used a disk with degrees but it was hard to centre and to see the the values and I was alone.

Bela 08-09-19 06:26 PM

I did the job again - but this time I calculated the radians and used two pieces of tape to the see the distance from TDC and BDC. This time it was fine. So I adjusted the valve clearance for late 403 camshaft. Next week I'll perform a cylinder leak test for my peace of mind.

Bela 09-09-19 08:39 PM

I did the leak test and the results are between low and moderate. I guess no reason for heartbreake.


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