Well it was good while it lasted

I pulled my injected bike into the shop this evening for an after trip inspection.

The engine I installed this spring was basically an experimental engine I built from parts I had on the shelves -mostly spares from racing. I had originally planned to run it as a 0 degree twin. [twingle of sorts] I had dropped that idea as I didn't think the trans could handle it.

It has a 91mm stroke and an 81mm bore. The extra stroke was gained by offset grinding a stock crank that had a big dent from a broken rod. It is .100 undersize and reinforced with a hollow pin through the big end. It has a steel flywheel.

The rods are made by Carrillo. They are spares I had made for my racebike around 15 years ago. 6.4 inches long with an ultra-light no bush small end that is copper plated. [no DLC back then]

The pistons are JE's that were spares for the same bike. Semi-short skirts and high pins. Ceramic coated tops and skirts.

The barrels are stock iron with nodular iron liners from Advanced Sleeve. [non-austentic]

The cam is a Webcam 12a grind running on stock lifters ground with a 4 inch radius to make it a little less aggressive. It runs in needle bearings set up with inner races to protect the cam. Maney pushrods and RD springs.

Stock cases and a head with port inserts and 1.5mm oversized intake valves.

Horsepower on the last dyno run was low 70's at the rev limit of 6200 rpm as I didn't want to take chances with the crank. The engine is without a doubt the strongest feeling Norton motor I have ever run on the street.







Now the bad news -

The leakdown test after the first start and heat cycle was 8 percent.

After 500 miles the leakdown tested at 5 percent right and 6 percent on the left.

Now at 9800 miles the leakdown shows 15 percent right and 25 percent left. Not good.

The engine still runs strong but it was using a little bit of oil and I was getting a small amount of oil from the breather dripping on the air cleaner. I first noticed that on the way back from Birmingham. The engine has also gotten pretty noisy for the first 30 seconds when started on a cool morning.

I guess I better be getting my billet motor done for next summer. Jim

Jim, any thoughts on the reason for the big change in leakdown with a relatively small mileage? Can you hear if the leakage is mostly ring blow-by or past the valves?
I have an engine that is starting to show high leakdown, both from valves and rings, using roughly a US quart per thousand (out the breather), however it has just over 50,000 miles on the top end. Hate to tear it down as it runs great.

Glen

worntorn said:

Jim, any thoughts on the reason for the big change in leakdown with a relatively small mileage? Can you hear if the leakage is mostly ring blow-by or past the valves?
I have an engine that is starting to show high leakdown, both from valves and rings, using roughly a US quart per thousand (out the breather), however it has just over 50,000 miles on the top end. Hate to tear it down as it runs great.

Glen

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There is zero leakage past the valves or head gasket. I suspect it is cylinder wear. I don't see any scores in the bore using a boroscope.

I don't plan on tearing it down until the new motor is finished. Jim

Frankenstein tale engine. Ring gap changes? Ring edges rounded? Luck of the draw on bore hardness? Kn type 'filter' element?

Jim's engine, made from leftover parts he had laying around would stomp 99% of the Commandos out there.

:shock:

Jim. It may be the aluminum plug for lock up the wristpin expands and damages the cylinder liners??

I like your cam lube system

swooshdave said:

Jim's engine, made from leftover parts he had laying around would stomp 99% of the Commandos out there.

:shock:

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I was thinking the same thing. 70+ HP out of spare parts Those are some pretty good spares tho.

Kvinnhering said:

.......I like your cam lube system ......

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+1 & interesting post, thanks for putting it up here Jim

Jim
Looking at your 12a. I see that the center between the lobes got beefed up. Did webcam do this to stop camshaft bend?
Tom
CNN

CanukNortonNut said:

Jim
Looking at your 12a. I see that the center between the lobes got beefed up. Did webcam do this to stop camshaft bend?
Tom
CNN

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No, that was the experimental twingle cam. It had been cut in half and turned so both cylinders would fire together. The ends were tapered and pulled into a sleeve that you see in the center of the cam. I never ran it that way. Jim

Jim I've a bore guage to send you to mic bore shape/wear to help ID reasons it wore out in less than two rear tires on the least wearing constant hyw travel conditions. Two famous things accelerate bore wear [besides pin caps which leave witness mark paths] is fuel richness washing bores off or insufficient air filtering. You impressed us with your super duper fueling control. Wes and I and some fleet operators were not impressed by periodic interval hand oiled low restriction racer cutie pie elements. Real oil assisted filters bubble air through oil bath. Btw 70+ hp on a Commando should allow good pull to ~ 135 mph and break under 12 sec 1/4 mile, if bike/pilot mass under 550 lb.

hobot said:

Jim I've a bore guage to send you to mic bore shape/wear to help ID reasons it wore out in less than two rear tires on the least wearing constant hyw travel conditions. Two famous things accelerate bore wear [besides pin caps which leave witness mark paths] is fuel richness washing bores off or insufficient air filtering. You impressed us with your super duper fueling control. Wes and I and some fleet operators were not impressed by periodic interval hand oiled low restriction racer cutie pie elements. Real oil assisted filters bubble air through oil bath. Btw 70+ hp on a Commando should allow good pull to ~ 135 mph and break under 12 sec 1/4 mile, if bike/pilot mass under 550 lb.

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Don't worry, I have a fine bore gauge.

Mixture was well controlled, air filter is not a problem, it's well oiled and there is no signs of dust in the intake, it has never ran hot or with incorrect timing. The motor has been used with care since it was installed. There are no score marks that could indicate a problem with the pin buttons.

I suspect I know what caused the leakage but I will not know for sure until it's down. Jim

Thanks for posting this, Jim. I guess we'll have to wait till you tear it down to see what really happened. If nothing else, your results have encouraged me to think seriously about doing the BoreTech carbide treatment on future big bore engines. My experience with 81 mm bores has been pretty good on the race bikes, but they don't get the kind of mileage that your street bike does.

Ken

Well I guess maybe I will go ahead and tear it down. The more I think about it the more I wonder if bore wear is actually the problem. With the wear resistant nodular liners they should not be worn this early.

One thing I noticed when I was on the cross country ride. When I would shut the bike off and restart it when it was hot I would get a single heavy "ping" as it passed TDC the first time over.

In the past I had been firing the plug at 10 degrees after TDC when cranking. With the new engine the first spark is at 7 degrees after TDC. I am also using ultra-light rods this time instead of standard Carrillo rods.

I wonder if that engine knock [ping] when starting has bent those ultra light rods.....

Time to pull the head.

Just teasing about tools to mic bore size & shape but you found nothing obvious there so then maybe valve seats or cam lobes dissolving in stead ; )
Appreciate ignition time details but how often does that cause such fast leak down increase. Ring gap data requested to compare notes. Trixie new ring job with slight hone in old bores is still ~.0005" under size bore on the .040" over bores and resealed well but thinking cheaper to Bore Tech now than re-bore risky .060" over or another cylinder by me or next owner.

Re: Well it was good while it lastede gotten

so Jim, you're thinking too much advance bent a rod. Is that correct?
It is certainly a possibility.

On your last trip, could you have gotten some bad fuel ?
I figure that it would have to be pretty low quality to cause enough pre-ignition to cause a "knock" that hard.

Here is what I found.
Rods are straight.
Bore wear is not real bad. They are worn about .0007 oval. There has been very little cylinder contact between the piston above the top ring and the cylinder. A little more on the left side than the right.







The only real visible problem is the top ring end gap has grown from .016 where they started to .028 on the left and .024 on the right.
Since these pistons were originally built for racing they are made with radial gas ports. Note the cutouts above the top ring in picture 2. This is likely the reason for the fast ring wear.

The pistons also rock quite a bit and when they rock to the extreme the rings lose their seal against the cylinder wall. With the leakage tester in the cylinder I could hear the leakage change when the pistons move around before and after TDC. I also found that if I slowly turned the crank back and forth until the pistons were setting straight in the bore then the leakage would drop down to around 15% on the worst cylinder and 10% on the cylinder with the tighter ring end gap. I could then stick a long screwdriver up through the sump plug hole and push on the bottom of the piston making it tilt, and the ring seal would be lost until I moved the crank around again.

So it looks like I am going to live with this until the new engine is done unless I want to have some new pistons made. Jim

Jim
What about going to gapless ring set. Just for the interim for engine change out???
Cheers,
Thomas
CNN

comnoz said:

Well I guess maybe I will go ahead and tear it down. The more I think about it the more I wonder if bore wear is actually the problem. With the wear resistant nodular liners they should not be worn this early.

One thing I noticed when I was on the cross country ride. When I would shut the bike off and restart it when it was hot I would get a single heavy "ping" as it passed TDC the first time over.

In the past I had been firing the plug at 10 degrees after TDC when cranking. With the new engine the first spark is at 7 degrees after TDC. I am also using ultra-light rods this time instead of standard Carrillo rods.

I wonder if that engine knock [ping] when starting has bent those ultra light rods.....

Time to pull the head.

Click to expand...

Sometimes a 'ping' can be a valve catching the cutaway in the piston.

CanukNortonNut said:

Jim
What about going to gapless ring set. Just for the interim for engine change out???
Cheers,
Thomas
CNN

Click to expand...

I ordered up a set of coated stainless rings. They should wear a little better than what was in it.
It's not going to help the ring seal when the pistons rock however -but neither would gapless rings. Jim