[Mgs] Timing adjustment on an 18GK engine

Sat Jul 10 05:47:18 MDT 2021

Hi WIlliam,
    There will be as many answers to your questions as there are readers, as there are many variables involved.
    It is my opinion that if the max advance, without vacuum connected, should be 32 degrees at 3500+.   That is shared by many.  Another of my opinions is that 10% alcohol makes no difference to the engine’s performance.  One can read adverts in British periodicals of the 1950s and 1960s in which the brands advertise that they are better because of the alcohol.   
    As to the fuel choice, that very much depends on where you are driving (hills, dales, flat country) and how you like to drive.  The workshop manual was written years ago, so its timing specs may or may not be valid today.   Fuels differ around the country, and certainly are quite different from those in 1974, so you end up selecting one that seems to work OK for you.  It is said, also, that fuel blends differ regionally in USA.
   One ends up setting the timing to what keeps engine and driver happy. We know that pinging/pinking is hard on the engine. One should avoid that by down-shifting as needed, checking that the timing is not over-advanced,  or by using higher-octane fuel.  
   Mine is 1972 18V, home-market pistons, some cleanup of heads and ports, with HIF and distributor rebuilt by Advanced Distributors (Jeff Schlemmer).  Max advance, w/o vacuum, is 32 degrees.    I find that alternating tanks of 89 and 91 (sometimes the same pump shows 93) keeps it happy. We have some hills in CT, so I listen carefully at 2500 rpm. 
   Over the course of a driving season, perhaps 4000 miles, the annual difference in cost of one fuel to another is slight. I try to err on the side of caution.
Bob


> On Jul 9, 2021, at 5:47 PM, wkilleffer at epbfi.com wrote:
> 
> Hello everyone,
> 
> My car is a 1974 MGB with an 18GK engine and HS4 carbs. The evaporative loss control and anti-run on controls are connected. The smog pump has been removed and the ports are plugged. The distributor is a Pertronix unit I bought several years ago. It's equipped with vacuum advance, which is working. The mechanical advance is also freely working. Not too long ago, I read that these cars, even the high compression ones, should be able to run well on ethanol-free 87 octane. This caused no small debate on the local British car group on facebook, but the consensus seemed to be that those who used E0 87 were satisfied and didn't have any issues from it. My last fill-up had been ethanol-free 93, and I need not tell you that running E0 87 would be far preferable. It was time for a fill-up, so I filled at at a nearby station that seems to sell decent quality stuff.
> 
> It appears to run well enough, but I have had a couple of issues come up where there was a low-speed but high load situation, like going up a short hill with a 15 mph speed limit. I could hear it pinging some. Downshifting will stop it, but that isn't always practical. So, I decided to check its timing. The Bentley manual and several online sources state that an 18GK is supposed to have its dynamic timing set to 16deg BTDC at 1500rpm. It's been a few years since I last set the timing, so I disconnected the vacuum advance and plugged the manifold port, and then got the car running smoothly at 1500rpm as indicated by the tach in the dash. It's all I have, so it'll have to do.
> 
> I expected the timing to be too far advanced at that RPM, but if anything, it was slightly retarded. If 16deg is between the 20 and the 15, the car was currently set at around 12deg. I adjusted it to an indicated 16deg, re-checked the idle speed, checked the timing again, was satisfied, tightened the distributor clamp and shut off the engine. I haven't yet test driven it, though at idle it sounded smooth at maybe an indicated 800 or 850rpm. For all I know, it'll probably have a little more spring in its step, though it hasn't seemed sluggish lately. I try to drive it at least twice per week, so it's not sitting too often.
> 
> Does anyone else run 87 in a high compression engine, or have I gone off on a fool's errand here?
> 
> Thank you,
> -William
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