Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties oil in rear cylinder

oil in rear cylinder

Post Sun Jun 16, 2013 3:18 pm

Posts: 16
strange thing that spark plug at rear cyl is oily ??
The motor is a newbuilt stroker (t&O flywheel and pistons)
Front cylinder is nice when i check the plugg.
Compression is good on bouth cylinders when cold

Had to file down 0.30 rings to 0,20 pistons, and it wasent perfekly strait but in tolerance..?.
can it be the cutout i made in bottom cylinder skirts for clearance of rods?

Anybody recogise this problem??


Post Wed Jun 19, 2013 9:20 pm

Posts: 497
Location: Six miles East of Cheney, Wa.
Possibly rings have not seated yet? How many miles/hours on the engine? Don't think skirts would do it. Run a hotter plug for now. Does she smoke from the rear cylinder? Were the rings in the front cylinder also filed to fit? If so, and the front isn't using oil...then that's probably not it.

Post Thu Jun 20, 2013 3:44 am

Posts: 202
Location: Middle England UK
There is one seller of T&O pistons who doesn't have all sizes of ring,and sugests using the next size up.
In my opinion,this is bad practice,the seated ring will not be circular,but eliptical.It will bed in eventualy,but part of the ring won't be as wide as the rest.
Think of it as a tube that is 0.010 bigger diameter.If you cut a slot along it's length and squeezed the ends together,it would no longer be round.
You can get the correct sized Hastings rings to fit,that would me my first move.
Were your cylinders honed before fitting? If not I'd do them before fitting the correct rings.
Too much oil in the bores of a new built engine is better than too little.Once the correct rings are run in,all should be well.

Post Fri Jun 21, 2013 12:53 am

Posts: 16
Yes bouth front and rear cyl have filed 0.30 rings, pistons are 70,18 mm and new bore is 70,28 mm
That with using oversize ring sounds like my problem..hopefully
I didnt have a clue there where other rings to buy.. Hastings rings any tips where i can buy those?

I Made a comp-test yesterday whit hot Engine around 60-65 on bouth cylinders. feels a bit Little..?
gona make some calulate on that..

I´m using a mikuni 34 carb, started with 1,5 turns on air scruew, but plugs where wery black then and bike was jerking a bit whene running at 45-55 miles/h, turned it out to 2,5 turns and it felt better
Going out driving soon and will adjust ignition to..

Thanks alot for good info :lol:
I been tuning old Volvo 121 for 15 years, but 45 flaties is al new to me :wink:

Post Fri Jun 21, 2013 9:50 am

Posts: 16
More info:
to awnser som previus questions: bouth cyl were smoking in the begining, but after tighting the headbults it stoppt,.

Just run 100 miles adjusted ignition buy the book but it ran wours than Before, advance it abit and it got better.
Still feel som minor jerking in sppeds around 45-55 miles/h. but when i go faster it disapers...
Less oil on rear cylinder when a chekt it today
60 psi fells low.
engin is a 4 7/16 stroke whit 70.28 mm bore, 82 cc alu cyl heads

Post Wed Jun 26, 2013 6:45 am

Posts: 202
Location: Middle England UK
Hastings rings are easy to find in the US and Europe.
Where are you?

Post Fri Jun 28, 2013 4:03 pm

Posts: 16
I´m in Sweden. still interested of Hastings rings.

Made around 200 miles now and made a comp test.
Got 85 psi on bouth cyl ! :D
You where right guys, rings has satteld and plugs starting to look dry. Tanks for info.

Tha problems whit jerking at crusing speeds has the mikuni 34..
260 mail jet, bought smaler ones that i drilled to 1.1 and ended at 1.2 mmm around 200 something
but it still runns to fat (jerkin) at low speed, pilot jet is 35 gonna buy new ones

Post Wed Sep 04, 2013 6:42 am

Posts: 783
Location: Victoria, Australia
If it's jerking at cruise speeds it's running lean. I'd also get those .030" rings out of the engine and get the correct size. I've just had some custom sized rings made at $14 each.

Your oiling problem is down to the ring misfit. If it were mine I wouldn't want to ruin the bores.I

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