Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board Still burning oil - considering parking it

Note: (I wrote this before I checked the site and the pictures have been removed.

When I saw the spark plug and heard the explanation I was ready to walk away from all this. I asked where will this all stop. It seems you have brought some passion and experience to this project, but have been unable to connect all of the appropriate dots. It is one long lesson, that will not be tempered with dreams of that Sportster that you mentioned. Hopping up one of those up has problems of their own.

First if I owned a Spitfire, that I expected to run on the street, the first thing I would do to it is remove those pistons. For a number of reasons, which I am sure in a quiet moment you could recite verbatim, running anything with 11 to 1 pistons is going to cause problems and I am here to say that those pistons, and the challenges they present, are at the root of your problems.

I invite readers to open Marc's flicker link with the picture of the BSA. Detonation has been the plague of this engine since the beginning. Some will look at the Carrillo rod and the rod bearing failure as a lubrication problem. While certainly a possibility, I always look around for all of the clues. One doesn't have to look very far. Just look at the burnt carbon on the under the dome of the pistons, especially on the side with the rod bearing failure. IMHO the rod bearing failure was not a lubrication problem, but caused by the ravages of detonation.

The domes of your pistons show that this motor is still experiencing detonation. Detonation is not your friend at anytime, but it can, and will, upset the ability for rings to seat. Detonation is a violent explosion and can split crankcases in half, break crankshafts, break connecting rods, and yes upset rings so they cannot seal. Detonation when the rings are trying to bed in will not lead to a happy experience. After viewing this, and hearing your explanation about the spark plug it all started to make sense. Before you set off spending money you need to think about how you are going to cure your detonation problem.

Successfully building a performance engine is not a collection of expensive parts, although some are certainly helpful. It is an exercise in understanding and making plans to control the heat that will be generated. Controlling heat, especially in an air cooled engine, is JOB ONE. The first thing you must do is limit the amount of heat created by unwanted detonation and this is done by limiting compression and/or the selection of the octane grade of the fuel to be used. Then you need to set out, and as Kevin Cameron says, "Toughen your engine against detonation." This includes removing all sharp edges, increasing the width of the margin of the valves, adjusting the width of the valve's seat contact area, selecting the correct grade spark plug, selecting an appropriate ignition advance curve, etc... And that brings us back to the spark plug and the heli-coil.

Why do I know all this... because in the past 50 years I have walked in your shoes...
John

The pictures are still there for anyone interested... just one album up from the "burning oil" album: http://s286.photobucket.com/user/bsaman/library/bsa%20rebuild?sort=6&page=1

I think this is the picture John referred to (piston on the left had spun bearing):


To put things into perspective for you guys, that rebuild took place in 2007 and 2008 and the bike has been smoking ever since. Not to the extent it is now (it was my daily rider for one summer) but I really started chasing the root cause in may of 2009 (first set of replacement rings).

The second that rod bearing spun, I inherited (literally, inherited) this bike along with some spares and its history of problems. The NOS high-domed pistons where part of the spares, so I used them. Simple as that.

I don't need high compression. I'm not looking for this:


Rather this (that's me on the front):


As to the reason behind the Sportster comment: I'm a Sportster guy. I love 'em. I have an 04 now which I've rebuilt (no ring seating issues) and had an ironhead in the past. And, while there are a few "British" bike mechanics in my area (usually Triumph guys that will do BSA) there are dozens (if not more) highly qualified guys that work on old HD stuff within a 15 mile radius of me.

Wow, that was REALLY close! You are lucky to have avoided a holed piston, and worse.

Thank you for clearing up the flicker reference, and posting the two pictures of you on the bikes. They reminded me of why some people have few problems using high compression pistons and others can't avoid them. The pictures are good reminders.

Here's why they are: Detonation is a violent event that takes TIME to develop. Brief for sure, but the whole process takes long enough that engine rpm is a big factor.

The guy, that's you, in the top picture is much less likely to experience these kinds of problems than what is represented in the bottom picture, you again with some happy siblings. The reality is 180° opposite of what common sense would tell you. One would think it would be the guy in photo #1 who would have the problem, but it isn't. It is the guy represented in picture #2 who is going to have all the problems with 11:1 pistons.

Detonation, because there is more time available for it to develop, will happen at lower rpm's, especially if the engine is being exposed to very high dynamic cylinder pressure due to being lugged, much more often than it will ever happen in racing conditions where the engine is turning a much higher rpm... At higher rpm's the typical dynamic cylinder pressure is lower (less heat to develop a case of detonation) and there just isn't the time for detonation to develop.

Street riding is done in the rpm range where you put the most load on the engine, where there is a lot of time for detonation to develop, and you are most likely develop detonation. That is why it is much harder to build a robust high performance street engine than one that is to be used on the track.

It was worse, did you look at the Carrillo rod?

You know I have to thank Marc for sharing this!!!! It isn't easy to wash your dirty laundry in public. If all this just gets one person to think, before he sets out to hot rod one of these old motorcycles, he has done us all a great service! I am not saying not to do it! I am saying that you cannot rely on other people to do your thinking. There are plenty of people who visit this site who have built very successful street hot rods, but there are things you can and cannot do.

Just to clarify, that first picture is my dad at about 1/2 my current age (circa 1969). As far as I know, gears and bearings were always the parts that were failing (based on the notes in his original parts book. The cover is as greasy as some rags I throw out).

I'm just looking to be that kid again in the second pic, with the big grin sitting on the bike, whether that's at 60 mph or 15 mph.

So, laundry list time. These aren't necessarily things I'm going to do, but if I were to lower the compression and assuming I wanted to ensure, as much as possible, that the burning oil gets addressed:

- Pistons + rings. Bore/hone was originally done with those pistons in hand. Would a +.020 piston be required at this time? What about the balance factor? Would it be affected if I get the pistons close to the same weight?
- Guides need to be re-checked? I'll check tonight to see if any fluid made its way past the guide, but I didn't see anything last night. Any other checks to try to get to the bottom of all the oil on the intake valve/runner?
- Fix the spark plug hole
- Which oil do I use? I've heard everything from cheap grocery store oil (very guaranteed to have the 'energy conserving' starbust), to the engine builder's "whatever I got on the shelf" (likely CI-4/SH, SG, or SL), to the stuff I have on hand (Joe Gibbs BR30, not API rated).
- Still suspicious of oil around the right-rear head stud. Oil was also on the fins rearward of this stud, showing that it was creeping up the stud.

Anything else? Thanks for sticking with me

If your just bimbling get some 7.5:1 pistons. Maybe even take the gearbox sprocket 1 tooth smaller. I ran mine with 7.5:1 and 19:47 when I first built it and it was quite peppy, flattened out at around 95mph when in good fettle. The smaller gearing makes it more difficult to accidently lug it around.

Some GPM pistons are around 400-430g, I was running +060 and they weighed in at 428g inc rings, pin etc. the lighter the piston the smoother it will be and the flatter the piston the better the combustion ( which is why modern vehicles don't have domed pistons or head chambers). If you have access to a milling machine you can lighten the pistons further!

If you do go with GPM, buy someone else's rings. Theirs are not good. The pistons are cast and would require a min .004" skirt clearance.

Or if you can find any original, hepolites, AE, federal mogul etc these are oem equipment.

I have orders to fill, but the method used to grind these old crankshafts requires that you use 20w-50 oil. This insures that your oil will have the proper viscosity (in the 10 range) at operating temperatures. 5w-30 is too thin for these applications and designed to be used with appropriate bearing clearances and crankshaft grinding procedures.

Modern crankshafts journals are ground to much closer bearing clearances, and longitudinal and diametric tolerances, and in such a way that reduces the chances these tight clearances will cause a problem. They even go as far as to polish the crankshaft so the metal tears, caused by the grinding, are all laying in the direction of rotation. You do not have a modern engine, made with modern metals and held to very tight tolerances. You have some thing that was made on worn out machines, with the cheapest material they could get away with and at the lowest possible cost. They just learned how to work with what they had and still get something they could sell. These are also derived from concepts that would produce 30 hp, or less, and preform reasonably reliably. All of the things that drive modern automotive technicians when they see the clearances, cylinder bore preparation with out 150-180 grit, 20w-50 oil, etc enable them to get the bike out the door and pray that it stayed out. I have seen reports that BSA was paying out in excess of $800 to dealers in warranty payments on a $1000. retail motorcycle. And no magic wand, super oil technology is going to improve on the original design!!!

Read what I wrote above about the Japanese Big 4 and there battle with SAE over modern oil!! Joe Gibbs 5W-30 break-in oil is designed for modern engines using modern design, cooling and machining practices. You want a 50 weight break-in oil (which will be in the SAE SB SC range) or a MOTORCYCLE oil rated SAE SG - JASO MA2. That is what you want to see on the can. NO starburst - period. For your BSA the JASO rating (slipping clutches) is not as important as the SG rating (no friction modifiers and more zinc) which is what was in existence when this motorcycle was made.

Because of the old engine designs, available metallurgy and manufacturing procedures, grey cast iron rings are most often offered in ring sets. Grey cast iron rings, not requiring a protective finish like chrome, are just what the doctor ordered when it comes to these old engines. They, and the cylinder bore, will lap in during the first few miles of engine operation.

Unlike modern steel and ductile iron rings, which due to the fact they are plated with a protective coating (neither are compatible with the cast iron blocks), our grey cast iron rings are not lapped round from the factory. They are as turned and final finishing is done in the cylinder during the first few miles. This is why we need to use such a coarse grit cylinder finish. If it is too smooth the rings do not seat and the cylinder glazes.

Neither can you hold the tolerances required to use modern steel or ductile rings without boring and honing plates top and bottom of the cylinder and close attention to dimensions both top to bottom and radially. You also should leave the cylinder lay around a couple of days before final honing. These cylinders have a mind of their own once you start cutting on them.

I have to do some work or my family is going to kill me...

You won't need a rebore and bigger pistons unless your cylinders are badly worn (they don't look it).I wouldn't bore a cylinder unless it showed 0.006" or 0.007" wear/taper.Just get a pair of 9:1 standard pistons if the bore is standard.You'll still need to check the clearance on both the new pistons,to make sure they're not too tight.

Radius any corners on the pistons crowns with a 1/8" radius,where possible.Weigh them to see if their weights are equal.You can file some off the bottom of the skirt on each side below the pin,to fix that within 0.5 grams.If they're lighter than the old pistons,I wouldn't be too concerned about it.

Building a hot rod for the street is a much different exercise than one for the track, if we were only to consider available fuel, but there are other factors to consider. To meet these challenges one must address the one thing that is going to cause you the most problems: detonation, and detonation induced pre-ignition.

For reasons I explained above, a street rider is much more likely to experience detonation than a racer. The street rod is operated at engine loads and rpm's where detonation is more likely to occur. Detonation is a time sensitive event, and if there isn't the time for it to develop it will not be a problem. Not that racers totally avoid problems with detonation, but with the higher rpm's used there is much less time for detonation to develop.

To have a good performing street rod you must do everything possible to prevent detonation. What you need to do is often the opposite of what you would do to make a completive racer that will only be doing hundreds of miles a season. The street rod will be called on to do that in one day.

The first place to start is to pick a sensible compression ratio based upon reliable availability of fuel. To be practical, and safe, this is the fuel available in any gas station in your area. You must remove all of the sharp edges inside the combustion area. This includes the valve pocket edges, exposed head gasket edges inside the bore ( a problem with larger cylinder over bores), valve margins, exposed spark plug hole threads, etc. ALL OF THEM!

You do not want any sharp edges that will retain heat produced by abnormal combustion (as no matter what you do an engine it will detonate once in a while) and detonation can lead to catastrophic pre-ignition (that dimed sized hole in the top of the piston). Abandon those narrow .040" wide valve seats in favor of ones closer to .080". All that extra air flow you get from those narrow seats will do you little good when the heat retained in the valve pre-ignites the incoming fuel charge and you put a hole in your piston. I would also provide .0005" additional valve guide clearance. So instead of .0015" on the exhaust I would use .002". Be sure to select a valve with a good wide valve margin. Those sharp edge valve might look like they will flow more air, all they will do is heat up and cause you grief.

Piston rings remove up to 75% of the heat absorbed into the dome of the piston from combustion. Forget the pistons skirts. You can use a piston where most of the skirt is removed as the skirt is there for support, not heat transfer. The wider the ring the more heat it will transfer. Because our hot rod is being used on the street you will inadvertently experience some detonation and you need all the ring width you can get. If you are going to have a long living street rod you want to get as much heat out of the dome of the piston as you can. Those modern narrow, low tension rings really look trick, but on a street rod they, and the piston they were used in, often end up on the shelf with all of the other offerings to the God's of Speed.

I would make sure that the cylinder preparation matched the ring material you will be using. 155-180 grit stones for grey cast iron rings. 280ish grit for ductile iron or steel rings, preferably leaving a couple of days between boring and honing and using honing plates. If I was using ductile iron or steel rings I would be looking for bore concentricity and taper to be less than .0002".

Don't use a stock camshaft, especially if you have upped the compression. This will develop more dynamic cylinder pressure and increase the chances of detonation. Select one of the milder street grinds. This will close the intake came later and reduce dynamic cylinder pressure. If you get the inlet and exhaust right you will get the additional power you were looking for.

Because you are much more likely to experience the conditions that allows detonation to develop, with a street rod I would run .001" additional piston clearance than I would with an all-out racer. In an effort to keep the rpm's up I would drop one tooth on the transmission sprocket. Remember it takes time for detonation to develop and by turning the engine faster there is less time. You will also reducing the dynamic cylinder pressure which reducing the chances you will have detonation in the first place. We are not building a cruiser...

I would use Morris, or equivalent vintage break-in oil, or if that isn't available a 4 stroke (4T) motorcycle 20W-50 oil rated SAE SG - JASO MA2 followed by a 4T Synthetic (Mobil 1 makes a 4T 20w50 motorcycle synthetic rated SJ JASO MA2 which we have had real good luck with in Vincent's).

Heat is the enemy of any air cooled engine. Your hot rod is no exception especially when used in normal traffic conditions. Don't build it for Daytona and expect it to survive Main Street. Be sensible, don't assume that you are going to get what you ask for (we live in a world where 99% of all engines have some form of liquid coolant). Make sure the person doing the work is qualified and knows that you expect the engine to perform on the street, not the track.

And IMHO a mild build with more cubic inches is one of the best ways to get get that performance you crave without the hassles of trying to get more performance with increased compression.