Blowing Oil After Top End Rebuild

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Greg Carter
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Re: Blowing Oil After Top End Rebuild

#61 Post by Greg Carter » Thu Dec 27, 2018 6:49 pm

We’re going to do a leak down and compression test for starters and see what comes from that. I don’t believe there’s a dyno in the area I can use to test the engine under road conditions as of now.

At this point I’m still stumped in that the problem only occurs after the car is driven in highway conditions at a fairly steady RPM for more than 10 minutes.

I didn’t see any issues like this prior to pulling the engine apart so I can’t imagine it would be a problem with the heads. We had them checked at a head shop and inspected them ourselves and everything was within factory tolerance.

When we pulled it down in NOV none of the rings were broken and it had the same issues as now. I doesn’t mean a ring couldn’t have broken since reassembly but I think it’s a lie probability.

I did find a piece of foam stuffed in the breather can tube when I had it apart the first time in OCT. It looked like somebody put it there to condense / collect oil vapor but it wasn’t factory. I would think that tube being plugged would’ve caused issues but it didn’t seem too.

The odd thing is, daily driving in traffic doesn’t have ill effects and the car runs and drives great. It’s definitely an on again off again problem.

Greg

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Re: Blowing Oil After Top End Rebuild

#62 Post by C J Murray » Thu Dec 27, 2018 8:03 pm

I would be surprised if Rusty missed any obvious problems. I think it must be something unusual.

Is the engine overfilled with oil Using a VW dipstick will cause you to put in an extra 2 or more quarts of oil.

Are the new pistons taller? Too much compression? Detonation causes ring flutter and that pushes a lot of combustion gasses into the crankcase. Are you using 30* pistons with 22* heads? That can cause detonation. Detonation is something that can come on suddenly and go away just as quickly. In your case maybe it only happens after a little time on the highway when combustion temperatures rise?
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Re: Blowing Oil After Top End Rebuild

#63 Post by Greg Carter » Thu Dec 27, 2018 8:56 pm

Mr. Murray,

We’ve compared the dipstick to other 356 dip sticks and they are the same. Unless there’s something we’re missing I don’t think it’s overfilled. It took just over 5 quarts to put the oil between the lines on the dip stick. That includes filling the filter can and a little extra for the PreMat full flow filter setup I installed.

While I didn’t QA the heads to see if they are 30* I’m pretty sure they are stock C heads. We CC’d everything and came up with a 9.2:1 compression ratio which is more than it was running before we put in new pistons/ cylinders. The old P/C kit was an NPR so it was probably around 8:1 - 8.5:1.

Greg

EDIT: while I know detonation is possible I would think running 91+ octane gas and 9.2:1 compression would probably preclude it.

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Re: Blowing Oil After Top End Rebuild

#64 Post by Dick Weiss » Thu Dec 27, 2018 10:16 pm

I never heard anything about piston ring rotation during my years; I do orient the gaps accordingly and making sure the oil ring gaps are "upward"--on both banks--including the top ring gap not in line w/the oil ring gap. The 3-or 4-piece oil ring will have the flat-sided pieces
w/their gaps staggered and not in line w/its "neighbor". No problems if its a 1-piece oil ring.

When tearing down an engine, I record the ring gap positions and re-chart their orientation when installing the cylinders. There were some unusual locations w/ring gaps in line w/each other and a lotta oil got by to get "cooked" in the combustion chamber(s).
Never disassembled an engine to view possible(?) ring rotation as my rebuild are on the road (seanonally) well past 20-years +.

Then there was an engine having several oil leaks due to the pressure relief valve having increased spring compression w/a spacer resulting
100 PSI! I add a hole in the side of the flapper box to access the cap w/the slotted tool for removal w/out removing the exhaust system and flapper box; I made a template to add the hole during rebuilds for a number of years just in case, but never had to use it since then.

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Re: Blowing Oil After Top End Rebuild

#65 Post by C J Murray » Thu Dec 27, 2018 10:21 pm

If you still are using the stock C cam with the 9.2 compression you may be on the edge of detonation. If you didn't do a very careful measurement of the actual TDC volume then you could be quite far off on the CR calculation. You may be higher than 9.2 CR.

It may not be detonation but I have no confidence that a crankcase breathing problem would come and go as you describe. Breathing problems are usually more consistent.
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Re: Blowing Oil After Top End Rebuild

#66 Post by Ron LaDow » Thu Dec 27, 2018 10:39 pm

Greg,
You've got an intermittent problem under certain loads.
I did a search for dyno services around you and found plenty of them and a quick perusal suggested that some were carb-and-distributor outfits.
If it were me, I'd call it time to stop guessing and start gathering real data.
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Re: Blowing Oil After Top End Rebuild

#67 Post by Greg Carter » Thu Dec 27, 2018 11:08 pm

Mr. LaDow,

I’ll look into a dyno that’s local and see if we can get the car on it. A rolling road type would be nice if I can find one.

Mr. Murray,

I’m wondering if my Schleicher RO 200 5 cam and Zenith carbs with the 9.5:1 compression JE pistons (that we measured / CC’d at 9.2:1) could be creating detonation issues after the engine gets a little warmer at highway speed. It doesn’t sound like there’s an issue but maybe....?

The car ran fine with this cam and big bore NPRs but it had a set of Weber 40IDFs at the time.

Greg

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Re: Blowing Oil After Top End Rebuild

#68 Post by C J Murray » Fri Dec 28, 2018 8:33 am

Do you have the cam specs, measured by you, no guessing?

Do you have accurate compression test numbers? High "pumping pressures" are a sign of a bad cam and CR combination. There are other factors that can also cause detonation.
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Re: Blowing Oil After Top End Rebuild

#69 Post by C J Murray » Fri Dec 28, 2018 8:43 am

A dyno test is a very good idea. Ask if they can apply a steady load for an extended amount of time which is what you need. Some dynos can only measure short acceleration runs which will tell you what power you have but won't duplicate 20 minutes on the highway.
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Re: Blowing Oil After Top End Rebuild

#70 Post by Greg Carter » Fri Dec 28, 2018 11:54 am

All,

Thanks again for the reples.

I have not measured the camshaft specs personally as intalled in the engine but it should be close to these numbers as posted on Willhoit's site (http://www.willhoitautorestoration.com/CamSpecs.php) for the camshaft in question:

Grind:
RO 200,5

EX-Duration:
244

EX-Lift:
0.333

IN-Duration:
244

IN-Lift:
0.333

L/S:
104.0

We are going to do a compression and leak down check in the next few days to see what we get.

Also, with regard to the compression ratio, everything was CC'd / checked with the proper tools and the static compression ration was computed.

I'd read somewhere (can't find the post now) where a compression ratio below about 9:5 - 1 with this cam / carbs might be on the edge of having detonation issues. I'm wondering if this is what might be happening now?

What I don't understand is, since the case wasn't split, the cam specs should be the same as they were prior to tear down. The engine didn't blow oil everywhere and was running a lower compression than it is now due the NPR 1720cc kit being somewhere between 8:1 and 8.5:1 on the compression. It was running the larger Weber carbs than the stock C-spec Zenith carbs it's currently got on it though.

Weber 40IDF and SC / 912 Solex carbs seem to be the normal setup people use with this cam and P/C kit from reading other posts. Could swaping carbs back to Weber 40IDF's potentially help?

Greg

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Re: Blowing Oil After Top End Rebuild

#71 Post by C J Murray » Fri Dec 28, 2018 1:21 pm

Use caution when following the advice from me or anybody else who has not actually inspected your engine and has a good reputation. In other words, Rusty should be your primary mentor while we in the peanut gallery are very limited by the fact that we are not there.

My suggestions are just suspicions.

IF you actually have the cam that you think you have(markings are not always correct)...and IF it is installed straight up with 104/104 lobe centers(it could be far advanced and that is a problem)....the cam duration is not a problem with your CR if it was at the more common 108* lobe separation. Your 104 intake LC is 4* advanced from stock which means the intake valve closes early and that makes the cam mimic a shorter duration cam, sort of, and it has more overlap, probably to boost acceleration. Earlier intake closing is what gives you torque from a mild cam but the CR needs to be lower than if the intake closed later. Blah blah blah.

Possibly your previous 8.1-8.5 CR was well below the detonation threshold but 9.5 with fresh rings and fresh valve job is approaching Three Mile Island status?

Funny thing about detonation in that sometimes there are no physical signs that it happened. In the 90s I built a new race engine for my Yamaha XS650/750 road racer and went to the first race of the year at Roebling Road GA the week before our Daytona race. I was trying a new cam but most importantly I had shaped the JE pistons from unfinished crowns and with careful machining I achieved around 14.5 CR. It was truly bad ass. This was a WERA race and because we(me and my "team mate") had no history with them they put us back on like row 32 of the start. Oh well, not where you want to start in a 25 minute sprint race. The flag dropped and my bike was a rocket! Cracking the throttle out of every corner just made the bike leap past other bikes. Some of that was normal when you start in the back with the slow guys but this was different. I was inside the top 10 in less than 2 laps but then the bike changed. The throttle response went limp relatively speaking as heat had built up and the air cooling was overwhelmed. I did finish the race in 7th but I had to baby it a little to get to the end. The oil catch tank was pretty full of oil but there were no other signs of detonation and I simply cut the pistons down and the bike ran fine but not with the same torque it had at 14.5 CR. My point is that detonation doesn't always show on a teardown even when you are positive you had a bad case of it.

Roller crank haters should note that there was no damage to the roller crank in that Yamaha motor. I never had a roller crank failure in the Yamahas, BSA Gold Star, or Velocette that I raced for 10 years. Plain bearing cranks are a better design though.
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Re: Blowing Oil After Top End Rebuild

#72 Post by C J Murray » Fri Dec 28, 2018 1:25 pm

Oh, I forgot an important point... all engines detonate, even modern computer controlled engines. The difference is how long and how severe.
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Re: Blowing Oil After Top End Rebuild

#73 Post by Rusty Ferrell » Fri Dec 28, 2018 1:40 pm

Greg dropped the car off yesterday and I was able to do a leakdown and compression test this morning on a cold engine.
Leakdown on all 4 cylinders was zero 100psi in and holding on zero percent leakdown. Compression reading was 140 WOT on all 4.
What concern I have at the moment is the spark plugs look a bit on the lean side which could show itself at steady state driving. We checked fuel level and main/idle jets which were 130/55. My jet gage has been beamed up so couldn't confirm jets sizes. Any jet suggestion running this configuration would be welcomed. If I'm able to locate my jet gage I'll open a set up to 140 and give them a try.
Happy New Year to all you out there. One heck of a hobby.
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Re: Blowing Oil After Top End Rebuild

#74 Post by Rusty Ferrell » Fri Dec 28, 2018 1:50 pm

leakdown.jpg
Same on all cylinders.
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Re: Blowing Oil After Top End Rebuild

#75 Post by C J Murray » Fri Dec 28, 2018 1:52 pm

140 psi is not excessive. Hmmmm.

Whatever the little spec book says for Super of C Zeniths should work. I usually run C jets without problems but I don't run that cam. If it looks lean give it some more fuel and try it out.
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