engine reliability

[jdugen]

I have fought with two problems over the last 30 years! <br />One, poor electrical supply, (fit a BMW field coil 3 phase alternator) and piston wear at the high speeds British motorways demand.<br /><br />I need the engine to be reliable at cruising speeds of 70 -80 mph or its playtime for the idiots who populate our roads.<br /><br />On every engine I have seen that is used fairly hard, the rear face of the pistons show wear and tearing of the skirt. This is the area that seizes in extremis.<br /><br />Obviously, this is the thrust face of the piston, the very area that is shielded from the cooling air stream. The way the engine spins also throws the spray from the big end oil supply towards the front of the cylinder.<br /><br />It is easiness itseself to fit an augmented oil supply to the rear face of the pistons.<br /><br />Tap into the oil pump at the oil gallery with its plug. lead an oil line around the back of the motor and into the 'well' of the gearbox. This is hidden by the tin cover for purists.<br /><br />Drill and tap into the rear sloping face of the crankcase. This can be done with engine insitu, but is, obviously better done on a stripped engine. A 'T' piece unit will llow the feed to be taken to each cylinder.<br /><br />However you do it, (I actually used the oil breather inserts under the carbs) arrange for a small diameter pipe to angle upwards and rearwards into the cylinders. The oil presure is more than sufficient to squirt fresh oil directly at the high friction area at the rear of the cylinder and does NOT affect oil supply to the rest of the engine.<br /><br />I have also fitted an oil cooler unit for serious peace of mind, but can assure one and all, that you will have a much happier engine if you undertake this mod.<br /><br />John Dugen<br /><br /><br />

[green62belair]

Hello John,
Do you have any pics of your installation?
Regards,
Kevin

[305]

did i read that right , you are running a 305 honda 80 miles per hour? or do you mean kilometers per hour?

[Phil-UK]

Hi John

I go along with the desirability of 70-80 mph cruising on the motorways and my '72 will do it but
is revving quite hard and based on experience of friends who've run 72/77s since the late 60's
occassional "nipping up" isn't unknown. I prefer cruising at @60mph for any distance on A or B roads.

What you're suggesting sounds a bit like the mod mentioned in an old copy of Cycle where they
tested the Webco 350cc kit and said that when racing they had problems with piston skirt seizures
and resolved them by drilling into the cylinders from the oil gallery that runs across the front
of the cylinder. They speculated that the long skirt on the piston meant there were parts of the
cylinder that were never exposed as the piston moved so got no oil spray.

What position relative to the piston stroke have you put your extra oil feeds in at ?
I would have thought you wouldn't want the rings going over the hole ( even though its small )
or have you found is doesn't matter ? How long have you been running this set-up for ?

I wonder if reducing the piston skirt length - ignoring the extra slap - would have a similar effect ?
I'm guessing that any CB72/77 based racers - which would be under more stress - around now
are running shorter forged pistons so have they found the need for extra lubrication ?

Of course a viable 5-speed road cluster would take some of the stress off the engine as we could then gear for top running higher .. roll on that Lottery win !!

cheers

Phil

[jensen]

Hi,

Here in the Netherlands I have the same problem, if you want to ride your CB72 safe on the road you need the speed, and here in the netherlands that is around 120 to 140 km / hour. (75 miles/hour to 85 miles/hour).

It's normal wear you talk about, back in the seventies it was normal to do a topend overhaul every 10.000 to 20.000 km. At high rpm wich go alonge with these speeds exsesive wear on piston skirts is common.

You can do several things about this wear at the back side of the pistons, one of them is using modern oil

Use, as mentioned in our earlier conversations John, a full synthetic 10W50 oil, this oil stays on the pistons under higher tempertures and pressure and does the job where a minaral oil will fail.
The only thing with synthetic oil that is doesn't work with the oil filter, and that's why I converted from the centrifugal filter to a modern paper filter and change this filter every 2000 a 3000 km, including oil change. I wrote about my modifications earlier, and I can do that again if you're intrested.

Pistons in my CB72 don't show this wear anymore, I last checked the internals after 25.000 km.
Even the valve surfaces where clean and nice, compression beter than measured after 2000 km after complete rebuild.

Furthermore using full synthetic oil the clutch needs stiffer springs, and old gaskets should be replaced by new ones, otherwise they start to leak.

Jensen

[e3steve]

I have fought with two problems over the last 30 years! One, poor electrical supply, (fit a BMW field coil 3 phase alternator) and piston wear at the high speeds British motorways demand. I need the engine to be reliable at cruising speeds of 70 -80 mph or its playtime for the idiots who populate our roads. On every engine I have seen that is used fairly hard, the rear face of the pistons show wear and tearing of the skirt. This is the area that seizes in extremis. Obviously, this is the thrust face of the piston, the very area that is shielded from the cooling air stream. The way the engine spins also throws the spray from the big end oil supply towards the front of the cylinder. It is easiness itseself to fit an augmented oil supply to the rear face of the pistons. Tap into the oil pump at the oil gallery with its plug. lead an oil line around the back of the motor and into the 'well' of the gearbox. This is hidden by the tin cover for purists. Drill and tap into the rear sloping face of the crankcase. This can be done with engine insitu, but is, obviously better done on a stripped engine. A 'T' piece unit will llow the feed to be taken to each cylinder. However you do it, (I actually used the oil breather inserts under the carbs) arrange for a small diameter pipe to angle upwards and rearwards into the cylinders. The oil presure is more than sufficient to squirt fresh oil directly at the high friction area at the rear of the cylinder and does NOT affect oil supply to the rest of the engine. I have also fitted an oil cooler unit for serious peace of mind, but can assure one and all, that you will have a much happier engine if you undertake this mod. John Dugen

Here in the Netherlands I have the same problem, if you want to ride your CB72 safe on the road you need the speed, and here in the netherlands that is around 120 to 140 km / hour. (75 miles/hour to 85 miles/hour).

It's normal wear you talk about, back in the seventies it was normal to do a topend overhaul every 10.000 to 20.000 km. At high rpm wich go alonge with these speeds exsesive wear on piston skirts is common.

You can do several things about this wear at the back side of the pistons, one of them is using modern oil

Use, as mentioned in our earlier conversations John, a full synthetic 10W50 oil, this oil stays on the pistons under higher tempertures and pressure and does the job where a minaral oil will fail.
The only thing with synthetic oil that is doesn't work with the oil filter, and that's why I converted from the centrifugal filter to a modern paper filter and change this filter every 2000 a 3000 km, including oil change. I wrote about my modifications earlier, and I can do that again if you're intrested.

Pistons in my CB72 don't show this wear anymore, I last checked the internals after 25.000 km.
Even the valve surfaces where clean and nice, compression beter than measured after 2000 km after complete rebuild.

Furthermore using full synthetic oil the clutch needs stiffer springs, and old gaskets should be replaced by new ones, otherwise they start to leak.

Jensen

Good tips from both you guys. I experienced a seizure during my delivery ride across Spain a year or so back, whilst slipstreaming a bus on the autopista. After CB cooled off a bit I stuck to slipstreaming rigs; the buses yomp along at 110-115km/h -- the trucks at a more sedate 100 (62mph). The ol' CB couldn't sustain the higher range for too long. And it was a 13-hr ride! I thought about banging off a quickie before the feeling came back to my hands, but didn't have the time......

[Vince Lupo]

Hi,

Here in the Netherlands I have the same problem, if you want to ride your CB72 safe on the road you need the speed, and here in the netherlands that is around 120 to 140 km / hour. (75 miles/hour to 85 miles/hour).

It's normal wear you talk about, back in the seventies it was normal to do a topend overhaul every 10.000 to 20.000 km. At high rpm wich go alonge with these speeds exsesive wear on piston skirts is common.

You can do several things about this wear at the back side of the pistons, one of them is using modern oil

Use, as mentioned in our earlier conversations John, a full synthetic 10W50 oil, this oil stays on the pistons under higher tempertures and pressure and does the job where a minaral oil will fail.
The only thing with synthetic oil that is doesn't work with the oil filter, and that's why I converted from the centrifugal filter to a modern paper filter and change this filter every 2000 a 3000 km, including oil change. I wrote about my modifications earlier, and I can do that again if you're intrested.

Pistons in my CB72 don't show this wear anymore, I last checked the internals after 25.000 km.
Even the valve surfaces where clean and nice, compression beter than measured after 2000 km after complete rebuild.

Furthermore using full synthetic oil the clutch needs stiffer springs, and old gaskets should be replaced by new ones, otherwise they start to leak.

Jensen

I'd be very interested to hear about your oil filter conversion!