ET: Engine (Twin) How Much Compression Reading Should A Twin Have & Leak Down

[CarlHungness]

I did a compression test on my Rapide. Throttle held wide open, snap on tools were used and do not use the type of gauge where you hold it over the hole. It needs to be screwed in. Mine screws in. Both plugs removed while performing the test. I did one cylinder at a time. Front was 135 p.s.i. and the rear was 145 p.s.i. I think I may have been able to squeeze a little more out of the front if I gave it a few more kicks. Can't remember but I'm pretty sure I have MK 1 cams. Hope this helps, Alyson

Mine screws in and it has been at 90 for many years because we had to put compression plates under the cylinders..SIb Biberman and Bill Jean did the rebuild..actually Sid didn't do anything except collect money. The pistons just touched the valves after the rebuild, I didn't know it, broke a couple of rockers, figured out the problem, Jean did not put plastoline on the pistons to check them..took engine back, made the mod and it has run just fine ever since. But at the time I did not know how much compression a good engine should have. But mine has started and run well for about 35,000 miles at 90 until last summer when I couldn't start it , and that's when the current headache began.

 

[fogrider]

You've succeded with the fuel level tests, well done. Near enough to not stop decent running and fine tuning can be done as and when. What's next ? I've just had all sorts of issues with ignition, Boyer Bransden very helpful, system proved OK, I finally discovered both HT caps had gone faulty , HT leads copper core so I did'nt suspect the leads - it was the caps all along ! Non-resistor types too, can't be at fault, surely.......
Only found after Boyer suggested a resistance check on the leads.
Cheap imitation plug caps. Should have guessed !

 

[CarlHungness]

You've succeded with the fuel level tests, well done. Near enough to not stop decent running and fine tuning can be done as and when. What's next ? I've just had all sorts of issues with ignition, Boyer Bransden very helpful, system proved OK, I finally discovered both HT caps had gone faulty , HT leads copper core so I did'nt suspect the leads - it was the caps all along ! Non-resistor types too, can't be at fault, surely.......
Only found after Boyer suggested a resistance check on the leads.
Cheap imitation plug caps. Should have guessed !

Seems as though it reached the stage where one says, "Well it has to run." One end of my KS spring must have
twisted a bit, broke and wound itself up amidst the innards. Finally got the cover off, waiting for new spring. Have it
timed at 35 with the rebuilt Lucas and will once again give it a go at end of week. Have double frustration now as I'm just starting to oxy weld .063" aluminum and blowing holes with seemingly right tip and setting. Am punishing myself
to the point of flagellation it seems. Held a spark plug to the Britax bar with the Lucas and can see spark by the way,
and don't know what else to do to the fuel system.

 

[fogrider]

Can't get oxy welding .063 ally right ? I have to tell you Carl, you are expecting too much of yourself because very few people can !.

 

[CarlHungness]

Can't get oxy welding .063 ally right ? I have to tell you Carl, you are expecting too much of yourself because very few people can !.

There are hundreds of panel beaters across the world who can oxy aluminum. It's one of those disciplines that as soon as you get the 'mixture' right, you're on your way. The mixture is knowing what tip size to use (I'm using .043"), how much oxy...2 lbs, how much acetylene (or hydrogen) 2 lbs and being able to 'see' when the material just gets shiny.
You have to have the proper goggles, which I have. They used to make Burt weld lenses during WWII that eliminate
the orange glare from the flux, and TM technologies now makes a very good clone...about $275 US. It'll take me a while, but I'll get it down one day. So far I'm blowin' holes. Just have to get the torch within a nickel's height of the material. And, the coupons I'm practicing on probably are not large enough to absorb much heat. One should use 12"
square and I've been using 3' x 6". If someone learned it, I'll learn it eventually. If I stop now I know the outcome, and
that isn't in my personality. It took me 6 years to move from 3rd chair to 2nd chair in the orchestra with the violin
I built, but I didn't give that up either.
Regarding the Vincent I'm out of options on what to try next. My KS spring should be here tomorrow and will
start the process all over again. If it ran once, it'll run again. Seems like it is just not getting enough fuel, and then
when it does start, momentarily, it seems like it runs out of fuel. So do I have a vacuum leak I can't find? I've ticked off the best Vincent mechanic in the US, Glenn Bewley and he doesn't want any part of me now, and has been a friend for 30 years, so this is a costly hiccup.
He says 90 lbs compression is enough to run it, and it was running, and it sure seems like it has compression enough to start it, it's no easier to kick than ever before. I'm a little ticked off at mechanic Bill Jean and Sid Biberman who charged me a whole lot to go through the engine years back and they gave it back to me with the pistons hitting the valves, thus had to put compression plates under the cylinders, thus the low compression.
Expecting a lot out of myself? That's what I do, the result of a dysfunctional upbringing whereupon I was branded as an idiot. But I overcame that, I have books in every state in the US Union and in every country in the industrialized world, and was told there is NO way I could be accepted to the University of Colorado as I didn't have a high school diploma, hadn't taken the SAT tests, and five years later I graduated from that school #2 in the class.
I'm not going to let some mechanical device, the motorcycle, or an oxy torch beat me now.

 

[lee_812d]

Does the front fuel level look a little high or is it the angle of the picture? It looks like it may be over that bottom section and so you'd expect it to overflow out of the little hole. If it is over that level and not overflowing then may be it should be or it could indicate it is not getting into the carb, or the hole is blocked etc. Or the front could be rich even if not overflowing (I've forgotten where we've got to!).

 

[CarlHungness]

Does the front fuel level look a little high or is it the angle of the picture? It looks like it may be over that bottom section and so you'd expect it to overflow out of the little hole. If it is over that level and not overflowing then may be it should be or it could indicate it is not getting into the carb, or the hole is blocked etc. Or the front could be rich even if not overflowing (I've forgotten where we've got to!).

Near as I can tell, the front is just a tad higher than the rear, but it doesn't overflow. Holding the tube and camera together is tough so camera angle isn't perfect.

 

[CarlHungness]

Can't get oxy welding .063 ally right ? I have to tell you Carl, you are expecting too much of yourself because very few people can !.

A-HA! Successfully got two full inches of weld done today on the .063" that looks perfect. The weld is attended by holes on either side, then another inch of weld, another hole, and so on and so forth. But, if I got two inches today, I'll get three tomorrow, and now can actually 'see' the puddle, so it'll be a matter of moving the puddle forward a lot faster than I thought, and realizing the time between having a good puddle and a blow out is approximately one half of a second. Have wanted to do this for years, and that was half the battle won.