Bristol Cars - Owners and Enthusiasts Forum  

Go Back   Bristol Cars - Owners and Enthusiasts Forum > Bristol Forums > 6 cyl Bristol cars

6 cyl Bristol cars Type 400 to 406 - restoration, repair, maintenance etc

BS engine specifications

Reply
 
Thread Tools Search this Thread Display Modes
  #1 (permalink)  
Old 03-03-13, 06:18 PM
Member
 
Join Date: Jul 2008
Posts: 107
Default BS engine specifications

I have been asked the following by my engine builder and I don't know the answers. Can anyone help?

Rocker ratio.
Duration and lift on a 40:80:8040 cam.
Valve lift
Spring pressures on the seat and on the head.

Any help would be appreciated. I can't find this info in the manual but I might be misunderstanding the terms.
Peter
Reply With Quote
  #2 (permalink)  
Old 03-03-13, 08:56 PM
Member
 
Join Date: Jul 2008
Location: Sydney, Australia
Posts: 384
Default BS Engine Specification

Peter,
I assume you need this information for a Arnolt Engine , BS1 Mk11 .

The cam fitted to that engine is a N340590
Its valve timing set at .002 cold (running hot at .009) is 32 , 72 , 72, 32
not the 40 , 80, 80 , 40 as sometimes stated .
Centre line is 110 deg

The way to check the cam is timed in relationship to the crank is by setting the No1 inlet valve clearance at 0.044 inch and check that the inlet valve opens at 10 BTDC .
There is a full valve timing diagram in the BS & C,D & D2 manuals .
I often have to re cut the cam sprocket keyway up to 7 degs to get the timing correct especially on B2 engines

Cam lift is approx .211
Rocker ratio is approx 1.5 to 1
Valve Lift is therefore 0.3165
less clearance cold .002
Effective valve lift 0.3145

Outer spring pressure at 1.028 is 54lb +/- 4lb
Inner spring pressure at 1.028 is 47.5lb +/- 4lb
Combined pressure at 1.028 is 101.5 +/-

I usually try to shim the original valve springs to achieve
Assembled height (Valve Closed) of 1.240in is 70lb + or - 4lbs
Assembled height (Valve opened) of 0.925 is 125lb + or - 4 lbs
but make sure you have between .050 & .080 spring travel left (when the valve is fully opened ) before the springs become coil bound

If your valves & valve seats have been faced a few times the shims required will be over 0.100 inch and the valve spring seat will lose its location around the valve guide. I have had slightly longer & stronger springs made to to compensate for this , to keep the pressures correct .
Depending on the use of the engine I shim these springs to acheive 80lb and about 150 lb .

I hope this is of some help
Regards
Geoff Dowdle
Reply With Quote
  #3 (permalink)  
Old 05-03-13, 10:56 PM
Member
 
Join Date: Jul 2008
Posts: 107
Default

Geoff,
That's great information. Can you clarify on the cam timing as the Arnolt Manual states that the cam timing is 40:80:80:40 and the timing diagram states the same.
Peter
Reply With Quote
  #4 (permalink)  
Old 07-03-13, 09:17 AM
Member
 
Join Date: Jul 2008
Location: Sydney, Australia
Posts: 384
Default BS Specification

Peter,
I have a Arnolt Manual and have found a reference to the valve timing at 40- 80 -80-40 in section 1 page 8 .
Where is the Valve Timing diagram ??

I suggest you get the engine builder to set up the cam at a centre line of 110 deg and see what the valve timing is at .002 and .009 clearance . This should clarify the timing , there should be a part number on the cam .

Geoff
can you email me a copy
geoff.dowdle@gmail.com
Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


All times are GMT. The time now is 10:52 PM.


This is the live site

Search Engine Friendly URLs by vBSEO 3.6.0 PL2