ET: Engine (Twin) Installing ET92 Inner Roller Set on Mainshaft
- Thread starter craig
- Start date
If you are asking about cylinder offset, the limit is probably anybody’s guess. How many actually get measured I wonder? Plus probably lots of case material sanded off over the years.
Also wondering what acceptable maximum rod offset from centre is acceptable. When folks shim the crank and split the difference between the rods, what sort of number ( offset) do they end up with? I’m also guessing that if 10 people measured the same crank for centring, we’d end up with 15 different answers.
Also wondering what acceptable maximum rod offset from centre is acceptable. When folks shim the crank and split the difference between the rods, what sort of number ( offset) do they end up with? I’m also guessing that if 10 people measured the same crank for centring, we’d end up with 15 different answers.
Hard to measure the spacer accurately given its location. My verniers won’t fit in there with the flywheels in the way. If I squeeze the rods together and slip in a new spacer as a gauge my guess is that they are within about .001” of each other and the one I used as a gauge measures 0.2730”. I installed the crank as you suggested and put the timing side case on with the small roller to keep the crank centred. I measured the gap between the rod and piston the same way as before. Pushing the rod all the way to the right and then measuring the gap on the left with feeler gauges. Then vice versa. I definitely got different numbers this time, but part of that was because the scroll was .0065” thinner this time. Now the numbers indicate the front rod needs to go .00525 towards the drive side and the rear rod needs to go .008 towards the timing side. So directions are the same, just less movement required. Splitting the difference at this point seems redundant. Measuring these things accurately seems a bit of a crap shoot….
I’ll be ok after I have a couple of beers.
I would have thought that unless the rods were actually far enough over to side load the pistons it won't make the slightest difference.
Hi Again, You are well within the tolerances of +/- 0.010 that I would be really happy with so have another beer and carry on the good work. I look forward to seeing the finished Bike,
Cheers Roy
Cheers Roy
The thing is, I don’t know what far enough over equates to for an old slow turning V twin. The majority of my experience is with Honda engines so Vincent motors have triggered a little paranoia. For the amount (and type) of use this engine will actually see, it likely doesn’t matter either way…. at least not to the current owner. The thing is…. most everything is new and I cashed in my left nut to pay for the fancy rods etc, so spending lots of time to make sure everything is as good as it can be. This isn’t the only thing I’m over thinking.
Personally I think it should be as close as possible to being centred. Then I’m not prone to nocturnal visions of uneven bushing wear… the pin thinking it’s a piston which taps the circlip out of place which sets off the inevitable expensive sounding death rattle. Robert and David have become my unofficial therapists…. like this engine, it’s a work in progress.
Thanks for your help Roy and may we both live long enough to see it run. It should have been finished a year ago, but somehow found myself in the midst of a renovation project. Things like standing on a ladder perched on top of 3 levels of scaffolding grinding mortar out of the chimney have taken priority.
The cases will be together soon…. cylinders, pistons, and heads are ready (minus paint), so at least one major milestone.
I'm currently working on a twin engine that has done about 30,000 miles since the crank was replaced where both rods are 3/16" offset towards the drive side. I'm only replacing pistons and cylinders. The point to note is that this amount of offset seems to have little effect on engine operation and life.
In all of the whole engine rebuilds I've done, I have never managed to get both rods perfectly central due to the con-rod offset being different to the crankcase so I usually split the difference between cylinders. Seems to work fine for stock engines.