piston ring gap?

The end gaps I'm using are on stock cylinders. If you find something different speced for your kit (like scabber's instructions above), I would go with that. I don't know how much I'd trust the guy answering e-mails from Mike's. I think he's just some flunky receptionist type that really doesn't have any tech knowledge. Read through the current Canadian needle jet thread and you'll see what I mean.
 
10-4 5twins
I am going to get the measurements and post them before I install them.
Getting them right is more important than how quick I can get it finished.
Thanks Guys for all the help.
 
The top compression ring should have a dot and bevel on the inside. Dot and bevel facing up toward top of piston. The second compression ring on my ring set had no dot and looked symmetrical. Pay attention to the oil expander ring make Shure the ends butt and not overlap hard to tell they tend to overlap and look like they are butted. If you don't have a ring expander good luck on installing the rings.
 
Hey scabber. I will make sure Brother.
everything is here. no over lap on the oil expander :thumbsup:
Thanks for the help Man. :)
Now I have to go finish mowing yard.
 
scabber said:
The ring gaps on the original mikes instructions. Minimum ring gap is 0.3mm (.01181) Maximum compression ring end gap is O.07mm (.0030). Ring end gap is checked with the piston ring placed squarely in the bore at leas 1/2" into the bore These are what Mikes instructions gave. I will leave it to the experts to comment on the numbers. The O.3mm looks like oil ring numbers.
Click to expand...

scabber said:
I bought the bigfin kit when it first came out and mike was mike. His instructions reads. Always check piston to cylinder clearance and piston ring gap before assembly. Piston to cylinder clearance is 0.06mm (.00236") Maximum clearance when new is 0.07mm. (.00276") Minimum clearance new 0.05mm. (.00197). Minimum clearances above should only be used if initial break in is done when weather is cool. A 200 mile break in period is recommended and the oil be changed at 50-100 miles. Measure piston to cylinder clearance at 90 degrees to the piston pin with the piston in the bore and at about 1/2" into the bore.
Click to expand...

I took the pistons and jugs to a machine shop to get measured and they are gtg.

I measured the ring gaps on one set of the rings
top ring .008" .2032 mm a little tight
2nd ring .011" .2794 mm a little tight
the 2 oil rails were the same at .014" .3556 mm way to wide :(

 
Your oil rings are probably fine. If you look at the specs, you'll see they're allowed to be much larger than the two upper rings. If the rings were tight and needed to be filed, and you had the option to set the gaps where you'd like, then of course you'd make them a little tighter.
 
Okay that makes since 5twins. Thanks Brother!
I never had new jugs and new pistons.
should I oil the rings at some point?
I used Valvoline 20/50 to lube cylinders after washing off the machine and storage oil.
 
Hey Carbon, please excuse, switching into 'old school' mindset:

Back in the day, when building forged piston engines, we would up the bore clearance about .0005" per inch of bore, to allow for the larger expansion of the denser aluminium forging. Would also caution the customer to avoid overheat and try to break-in on cool days/mornings. If at any time the engine felt doggy or a slight loss of power (initial symptom of piston seisure), the customer should IMMEDIATELY drop throttle, pull in the clutch, and coast along allowing the engine to cool in that coasting wind. Then, cut ignition and pull-off to the side and let it cool to warm-to-touch before trying a restart.

During that period of history, piston cross-section shapes could be either circular, or oval, in an attempt to control expansion geometry. Hopefully, the oval profile would heat-expand to circular.

Okay, 'old school' mode off.

I'm sure modern designs have licked that old issue, but the piston seizure emergency procedure may still apply...
 
Right on Two Many. that sounds like what my best friend was telling me last weekend.
He used to build hot rod WVs. He was warning me about the difference between cast piston and forged piston expansion rates.
So with a worried chuckle. I said oh :shrug:
So I hope that have it figured out too.
 
Agreed on the increase in gap for performance applications. Don't worry about being too loose, worry about being too tight. I ripped the top off of a Keith Black hypereutectic piston early in my career because the top ring gap was too tight. I learned my lesson after that, granted it was a high silicone content casting (12.5% or higher) which would require a looser top ring gap since less heat is leaving through the piston. Now you can find the same scenario with forged pistons. All the major forged piston manufactures are using two basic aluminum alloys 4032 and 2618. I am not sure which you have. The 4032 is a high silicone content forging and will have less expansion and therefore a greater top ring gap. The 2618 is a low silicone content forging and resembles that of the old TRW pistons which will expand more and require a looser piston to cylinder wall clearance but will typically allow a tighter top ring gap.

I frequently cut compression rings to unheard of numbers to simulate accelerated wear and the one thing I have learned from this is that you really have to cut the crap out of them before you see any significant change in blow by readings. Looking at it from the other angle: I have seen little to no difference in power output by tightening up the gaps to risky clearances. As far as the oil ring clearance, The expander tension will have a greater effect on oil control that anything else. So, I think you are fine on the oil ring.

As for the top ring being .008", As I mentioned this sounds snug to me when looking at it from a performance application when using .004-.005" per inch of bore rule of thumb but I assume someone on here would have better knowledge on this than me when building an XS engine. If they have done it and gotten away with it then happy trails. You do deserve praise for giving a shit about your engine clearance when so many out there in the world have attempted the same without consideration of the consequences. I hope it runs like a raped ape Carbon.
 
Last edited:
Looking at the factory spec. like 5twins said your oil rings are ok. the min. .012'' (.3mm.) max. .06" (1.5 mm. The piston clearance probably more important. So if it could use more piston clearance a light hone of the cylinders will open the ring gaps some and give more piston clearance. Factory clearance and engine builder clearance sometimes differ.
 
They've been selling these kits for a while now, I'm sure they have the clearances figured out. If they didn't, they'd be seizing up on everybody. I haven't heard any bad reports on them.
 
I have heard of one failure because putting together without checking ring gaps. Acording to the builder it scored the cylinder badly. If piston to bore clearance falls within mikes spec. It should not be a problem with piston expansion. Like 5twins said they sold a metric ton of these. More than one put together nothing checked and worked I'm Shure. Your at minimum spec. so it should work.
 
I would put a shell #1 cam and new springs. Doan the turtle armor and run the snot out of it. Flat track style not the back of the pack for about 50 miles. That will seat those rings nicely. Change oil and your good to go. I really like the low end power of the cam. :D
 
Lots depends on the "builder" as well. Engine work should be done in a clean environment (or as clean as possible for a workshop). I cringe when I watch those videos where a certain English member is laying his engine parts all over his driveway, unprotected, in the dirt and rocks. His 1st rebuild failed shortly after completion. It may have been bad parts but it may have been all the dirt and rocks included in the assembly besides the parts that should be there.

Yes, you're going to want the new parts oiled for assembly, but not to the point where that oil flows out onto the gasket surfaces, negating the effect of any sealer you're using. For the cam and rocker contact surfaces, I use actual assembly lube. Other parts are just lightly oiled.
 
Agree with 5twins. I use WD40 on a lint free rag, wipe the bore before final assembly, a finger tip dipped in oil and rubbed on the piston skirts, and call it good. Rings seat in fast and everything works fine. I also (and friends who race) don't pussy foot around with breaking in. Do one heat cycle at a fast idle (3000rpm) to get everything up to temp (piston, valve springs, cam, etc.) and don't blip. Let it cool down overnight, retorque, then ride/drive/ dyno it with load. 1/4 throttle with engine braking a few times, again with half throttle, then full throttle. Change the oil and you're done.
 
I want to thank you Guys very much for your help in this matter. :thumbsup:
I am feeling much better about this.
I couldn't find anyone that has Piston Ring Installer/Remover Pliers in stock around here. I have a pair coming in in the morning. I also have latex gloves. will get lent free towels this evening. I will go out of my way to keep everything contamination free upon assembly.
Thanks again Guys!
 

Similar threads

v8-914
366 motor...Why can't I find parts?
Replies
1
Views
85
650Skull
650Skull
D
Cruzinimage Big Bore Pistons
Replies
5
Views
766
dps650rider
D
F
Cruisin Image rings issues
Replies
12
Views
672
atom4488
A
K
Running hot after BBK and total top end rebuild.
Replies
7
Views
723
kwhy3000
K
DB90
First time engine rebuild
Replies
17
Views
709
DB90
DB90
Back
Top