Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
Unless blatantly wrong or outdated, I think it preferable to stay with handbook procedures. This reduces the confusing diversity of info presented to newcomers. Although it is tedious to access the flywheel, the book method avoids the risk of significant over advance. If strangers are going to drive a car generous max manual advance is best not available.
At part throttle generous advance improves economy, but no one drives Sevens at part throttle!
The full manual range seems to be 25-30 deg depending on the lie of the linkage. Even for hand cranking spark does not need to be as late as tdc, so even with 20 deg full advance rarely retard beyond half way. The range of the early Ruby auto distributor, from stop to full rpm was only 6 crank degrees. As most pulling in Sevens is done using rpm, advance is near full most of the time.
Much depends on whether have a new relatively forgiving nitrided crank or not, and close clearance mains. Crank stress increases very rapidly with advance, and life is hugely decreased by increased max stress. The performance trade off for modest advance is often slight.
On my car at "speed" the spark could be moved aver a considerable range and the only thing which changed was the exhaust note and engine din.
Joined: Nov 2017 Posts: 562 Threads: 56
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Location: West Yorkshire
Car type: Type 65 1934 + RP 1932
15-11-2017, 07:21 PM
(This post was last modified: 16-11-2017, 09:42 AM by Colin Wilks.)
Hadn’t realised that my question would be quite so contentious!
My car is a 1934 Type 65 with the original high(er) compression engine, two bearing crank and splash lubrication. Chassis number is 193400 and engine number is 194013. The previous owner went to the trouble of swapping this engine out for one of the many spare units he had kicking around when he was using the car regularly. He then reinstalled it about five years ago in anticipation of sale. Maybe he was overly cautious, I don’t know, but I do know that a good way to risk knackering it is to rev the bollocks off it with too much advance. The PO has clearly looked after the car in the last five years - oil and grease appears fresh, but the car has hardly turned a wheel during that time.
I have calculated that my manual advance/retard mechanism provides about 8 degrees of movement at the distributor (10mm travel on a radius of 45mm), which equates to about 16 crank degrees. I have decided to set up the static timing at TDC with the manual mechanism at R. This will give me a maximum of 16 degrees advance BTDC, which allows me to start the car very easily and to use the full movement of the mechanism without risk of over cooking it. Having the manual advance/retard mechanism makes it very easy for me to establish the advance where the engine is happy to idle, so I can then reset the static timing at “R” which will give me some additional advance to play with.
My overriding objective is to establish the minimum advance I can get away with consistent with making respectable progress. I hope that this approach will ensure minimum stress on the engine whilst I get used to it.
I can then start working out if the Zenith 30 VE1 downdraft carb is up to snuff!
I’ve posted this to let people know what I’ve decided to do. I always find it annoying on forums when there's no end to the story.
Joined: Aug 2017 Posts: 2,748 Threads: 31
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Location: Auckland, NZ
Hi Colin
You obviously have a clear grasp and should find experiments interesting. Manual advance (including fitted as override) gives you something to do whilst waiting for acceleration, grinding up hills etc.
I am surprised that the manual range is less than the stock 1934 car but much depends on the lie of the levers. Can be arrange to be very non linear.
A light spring from the distributor is useful to take out back lash.
My comments applied more to Sevens generally, as did many of the other responses.
Any 65 today may or may not be all dinkum; the engine likely close to other common modified Seven engines.
Whilst on the topic, very retarded cars are reluctant to rev through gears and seem to gain rpm in surges. Contrary to what may logically expect, the exhaust with retarded spark sounds flat. In their day many Sevens had very worn mains and were run and sold very retarded. The car you eventually got was often very different from the smooth but lifeless one road tested!
For car engines generally I have never clearly established the relation between octane and spark advance. Some sources state little relation, others recommend a wide range. (ie Ford V8 40 octane 12 deg retard, 80 octane 12 deg advance)
If new to Sevens attention to the safety aspects, esp steering arms very worthwhile.
