bnw Posted May 12, 2011 Report Share Posted May 12, 2011 I've got to drive a newly acquired 1975 TR6 with a known bad camshaft 1600 miles home. The # 5 exhaust lobe is worn to the point where the expanded exploded air fuel charge cannot fully escape thus popping back through the intake valve when it opens really messing things up. If I pull the #5 plug wire, everything smooths out considerably because the un-exploded mix can escape through the exhaust opening. Do I have any other options? Should I try to eliminate the intake charge by pulling the plug or the intake push rod? I'm not really all that concerned about driving the distance on 5 unless I am missing something here. I once drove TR3 2600 miles on 3 with a burnt exhaust valve. The only thing that really suffered was fuel economy. At $0.29 per gallon, that wasn't all that bad. Quote Link to post Share on other sites
88V8 Posted May 12, 2011 Report Share Posted May 12, 2011 No harm done driving with the plug disconnected. Except a risk of blowing up the exhaust or getting shot at by an excitable policeman. I'd leave the spark plug in there, or all that inflammable mixture will be blown into the engine bay. If you plan to pull the engine, then no harm done driving with a bad cam lobe, otherwise I'd be unhappy at the thought of an extra 1600 miles of shavings in the oil, and I'd remove both inlet and exhaust pushrods (and lifters of course). Ivor Quote Link to post Share on other sites
bnw Posted May 12, 2011 Author Report Share Posted May 12, 2011 With both pushrods off, won't the vacuum created by the piston be transferred to the bottom end causing excessive oil to be sucked up to the top? Quote Link to post Share on other sites
88V8 Posted May 12, 2011 Report Share Posted May 12, 2011 With both pushrods off, won't the vacuum created by the piston be transferred to the bottom end causing excessive oil to be sucked up to the top? Hmmmm. Piston in a closed cylinder. What it sucks on one stroke it blows on the next. Will it blow past the rings or through the valve guides. Or both. Or neither. Or is it self-cancelling. Discuss. Ivor Quote Link to post Share on other sites
Alec Pringle Posted May 12, 2011 Report Share Posted May 12, 2011 If it doesn't already need a full engine rebuild, then it sure as hell will after 1600 miles on 5.5 cylinders, end of discussion. If it was mine I'd use a trailer, cheaper than trashing the lump . . . . Cheers, Alec Quote Link to post Share on other sites
bnw Posted May 12, 2011 Author Report Share Posted May 12, 2011 If it doesn't already need a full engine rebuild, then it sure as hell will after 1600 miles on 5.5 cylinders, end of discussion. If it was mine I'd use a trailer, cheaper than trashing the lump . . . . That's a pretty bold statement, Alec. Full engine rebuild? Today's cars are doing 8/6/4 on the road to save fuel. I can buy the additional cam shavings mentioned above, but I need a better explanation from you than end of discussion. Cheers, Alec Quote Link to post Share on other sites
Guest ntc Posted May 12, 2011 Report Share Posted May 12, 2011 Alec is correct if it ain,t knackered now it will soon be if you run it Quote Link to post Share on other sites
rpurchon Posted May 12, 2011 Report Share Posted May 12, 2011 I've got to drive a newly acquired 1975 TR6 with a known bad camshaft 1600 miles home. The # 5 exhaust lobe is worn to the point where the expanded exploded air fuel charge cannot fully escape thus popping back through the intake valve when it opens really messing things up. If I pull the #5 plug wire, everything smooths out considerably because the un-exploded mix can escape through the exhaust opening. Do I have any other options? Should I try to eliminate the intake charge by pulling the plug or the intake push rod? I'm not really all that concerned about driving the distance on 5 unless I am missing something here. I once drove TR3 2600 miles on 3 with a burnt exhaust valve. The only thing that really suffered was fuel economy. At $0.29 per gallon, that wasn't all that bad. i drove my car with a gradualy knackering ex lobe 500 miles before i figured out whot it was.no damage done id take the inlet push rod out and pull the plug out there will be no resistance but it will be noisy. only problem i can think of is **** been pulled in and out of the cylinder which could damage the bore. plus its already knackered,and your going to have to strip it anyway. i presume your in the states talking that kind of milage. richard Quote Link to post Share on other sites
bnw Posted May 12, 2011 Author Report Share Posted May 12, 2011 Denver to Northern Michigan. All down hill LOL. I would venture to say that those of us driving Triumphs for decades are inclined to take on the challenge. On the other hand, I'm guessing relative newbies think it will blow. When I was a young man driving TR's, I was always running possible disasters due to noises, oil pressure readings, etc thinking this would be my last trip. I learned through thousands of miles that these are wonderful, durable cars. BTW, I would not attempt this trip in an MG. Quote Link to post Share on other sites
john.r.davies Posted May 12, 2011 Report Share Posted May 12, 2011 Hmmmm. Piston in a closed cylinder. What it sucks on one stroke it blows on the next. Will it blow past the rings or through the valve guides. Or both. Or neither. Or is it self-cancelling. Discuss. Ivor Several high-end moderns resort to reducing the number of active cylinders when economy is needed. What do they do? No doubt the appropropraite injectors are disabled, but what about the pressure, as Ivor says? Could "Variable Valve Control" extend to having both open all the time? JOhn Quote Link to post Share on other sites
Alec Pringle Posted May 12, 2011 Report Share Posted May 12, 2011 It's a 60 year old basic design engine, long stroke with the resultant high piston speeds, and a relatively flexible bottom end and too much potential for crank movement. . . . and no 6 tends to get hotter than average anyway, so a cold pot next door isn't going to do the head any favours. Modern short stroke engines designed to chop out pairs of cylinders in response to demand are an entirely different kettle of fish. Not a lot to do with the price of Standard Triumph eggs. What you can get away with when it comes to a wet liner 4 doesn't necessarily wash with the 6, even in gutless wonder USA spec mode. A 1600 Vitesse lump was surprisingly tolerant of a defective cylinder, a 2000 less so, a 2500 less so again. Try nursing a 5 banger to the end of a rally, you'll soon enough get the picture. Best of luck, may the force be with you. Cheers, Alec Quote Link to post Share on other sites
bnw Posted May 12, 2011 Author Report Share Posted May 12, 2011 Thanks Alec. That's a lot better than "end of discussion" So, keeping RPM / piston speed low will help? 3K is about 60 MPH if I remember correctly. First sign of trouble will be.....? Quote Link to post Share on other sites
Alec Pringle Posted May 12, 2011 Report Share Posted May 12, 2011 You have 1234 and 6 cylinders firing, more or less equally, and 5 just being dragged along by the momentum of the rotating mass. That's a seriously unbalanced load, which will stress the bottom end. Potential bearing failure, or thrust washers departing, even a rod or crank letting go. Fuel input to no 5 will wash down and dilute the oil rapidly, increasing chance of bearing problems. Lack of oil and a cold piston rattling around will do the 5 bore no good. Meanwhile the head will have a cold spot above 5, lack of combustion, with hot 4 and 6 either side, so expect it to warp. The diluted oil isn't good for cam bearings either, nor for the oil pump come to that. The exhaust manifold won't be best pleased at having five hot and one cold primaries either. The first sign of trouble was the initial misfire. The next signs are likely to be terminal, one way or another. 1600 miles on 5 or even 5.5 pots would strike me as being up there with the loaves and fishes and raising Lazarus. If you do make it, expect a whole lot of wear. Cheers, Alec Quote Link to post Share on other sites
bnw Posted May 12, 2011 Author Report Share Posted May 12, 2011 Well, I appreciate your response and things could go as badly as you suggest but it does not have to be as bad as all that. The unburned charge should go right out the exhaust unless the lobe is completely gone. The cylinder, although dead, shouldn't be that much of a drag unless the engine is under a heavy load. Driving with the awareness of what is going on can keep the load at a minimum. Once again, when not under load, the heat from 4 and 6 should spread out to 5 thus lowering the temperature overall. I have no choice. I'm committed. Getting a car delivered to northern Michigan is very very expensive. The only thing I figure car screw this up is a motor already on it's last leg or I lose another cylinder. Quote Link to post Share on other sites
stuart Posted May 12, 2011 Report Share Posted May 12, 2011 Best get your triple A breakdown cover paid up then Stuart. Quote Link to post Share on other sites
Peter Cobbold Posted May 12, 2011 Report Share Posted May 12, 2011 BNW In that situation- recovery cost well exceeds rebore cost? - I would nurse the motor with the faulty cylinder idling ( pushrods out: both valves will be shut so no fuel or hot gas entering cylinder) and plug removed. [That is IF its a carb engine. Anyone trying this with PI will have to find some way of killing that cylider's fuel! and simply blocking the injector wont work as the following cylinder in the sequence will loose its fuel too.] I would add about an eggcup of oil to the empty cylinder (dont think of refitting the plug!), and top up every so often. And keep rpm well down - out of balance forces on the crank will fall off rapidly with lower rpm. So 2500 max. Heat? at light cruise power developed will be around 20hp or say 15kW, that means about 30-40kW of heat has to be dissipated. This is not a lot considering at full chat a highly tuned motor has to loose at least 300kW of heat, and that heating will come in bursts. I drove 60 miles with two cylinders idling due to holes the size of thumbnails in two pistons. No bore or crank problems at all. It is a bit noisy!! 1500miles? staying awake at 50mph will be your biggest challenge! Peter (whose TR6's crank is 280,000 miles old and still on standard journals with excellent oil pressure.) Quote Link to post Share on other sites
john.r.davies Posted May 12, 2011 Report Share Posted May 12, 2011 Got to say, if the cam is that worn, what are the in-block cam bearing surfaces like? The block is likely to be in need of the cam bore re-bored for bearings, cylinders rebored etc. etc. It's going to be an expensive rebuild whatever, so why not try driving it slowly home? Not much to lose? But 1500 miles @ 60mph = 25 hours straight of driving! Take a week off, bnw! Good luck! John Quote Link to post Share on other sites
Alec Pringle Posted May 12, 2011 Report Share Posted May 12, 2011 If you're committed, needs must when the devil drives . . . . But I'd stick to Peter's recommendation of 2500rpm rather than 3000, and avoid labouring up hills - OK 50mph is going to be pretty damn boring, but it's your best chance of reaching Michigan still rolling. 3 days man, 3 days . . . . A loud stereo will help here, you'll worry less if the music is drowning the protests from under the hood - there's not much you can do about them anyway ! Best of British, we'll all be thinking of you, fingers and toes crossed. Cheers, Alec Quote Link to post Share on other sites
Peter Cobbold Posted May 12, 2011 Report Share Posted May 12, 2011 Got to say, if the cam is that worn, what are the in-block cam bearing surfaces like? The block is likely to be in need of the cam bore re-bored for bearings, cylinders rebored etc. etc. It's going to be an expensive rebuild whatever, so why not try driving it slowly home? Not much to lose? But 1500 miles @ 60mph = 25 hours straight of driving! Take a week off, bnw! Good luck! John If BNW is lucky the worn cam lobe might merely be due to PO using modern ZDDP-free oil. Bores and bearings dont need ZDDP. Peter Quote Link to post Share on other sites
bnw Posted May 13, 2011 Author Report Share Posted May 13, 2011 NOW WE"RE TALKING!!! Whose next? Quote Link to post Share on other sites
Mk1PI Posted May 13, 2011 Report Share Posted May 13, 2011 Well I drove a PI from Cairns Queensland to Kalgoorlie WA (3420miles) in three days (and nights) back in 1998 - burnt number 5 exhaust valve at Toowoomba just out of Brisbane (80+ mph up the Dividing range approaching Toowoomba chasing a V8 Holden ) so drove the next 2300 miles on five cylinders at about 70mph , 20mpg and 500mpp of 20W/50 + quite a lot of caffeine). Biggest drama was running a front wheel bearing late at night but fixed that up in a borrowed BP workshop near Cobar at 6am when they opened for the day. Soon after replaced the valve but the head was cracked so rebuilt the engine a few months later - the crank and cam were both within limits even after this abuse. A carb car is even easier to nurse - remove pushrods and have an adventure!!! We are all too soft and precious about old cars! Quote Link to post Share on other sites
88V8 Posted May 13, 2011 Report Share Posted May 13, 2011 3K is about 60 MPH if I remember correctly. With no overdrive. If you have o'd then 60 mph = c2,200 rpm. I'd avoid sitting at 2,500 because the engine has a bad harmonic at 2,500. At least, mine does. These cars are pretty whirry with no overdrive. Woudn't want to do 1,600 miles in a year in a TR6 with no o/d. Something for your shopping list... I would nurse the motor with the faulty cylinder idling ( pushrods out: both valves will be shut so no fuel or hot gas entering cylinder) and plug removed. Reason I would leave the plug in is that the cylinder will then lubricate itself because as hinted earlier, with the pushrods removed, on the downstroke the piston will draw in oil mist from the crankcase and rocker box, and on the upstroke it will squirt it out again. I agree, plug out if it had blown a piston or burnt a valve or run a bearing. This will be quite an epic journey, one way or the other. Ivor Quote Link to post Share on other sites
Guest ntc Posted May 13, 2011 Report Share Posted May 13, 2011 (edited) Flush the engine,change the oil and filter to save any further damage, the bits from the cam will still be there Good luck Edited May 13, 2011 by ntc Quote Link to post Share on other sites
Peter Cobbold Posted May 13, 2011 Report Share Posted May 13, 2011 With no overdrive. If you have o'd then 60 mph = c2,200 rpm. I'd avoid sitting at 2,500 because the engine has a bad harmonic at 2,500. At least, mine does. These cars are pretty whirry with no overdrive. Woudn't want to do 1,600 miles in a year in a TR6 with no o/d. Something for your shopping list... Reason I would leave the plug in is that the cylinder will then lubricate itself because as hinted earlier, with the pushrods removed, on the downstroke the piston will draw in oil mist from the crankcase and rocker box, and on the upstroke it will squirt it out again. I agree, plug out if it had blown a piston or burnt a valve or run a bearing. This will be quite an epic journey, one way or the other. Ivor But with plug out the piston does no work, so loads on rings and cylinder bore less. Splash lube of cylinder bore keeps rings oiled near bdc. Six of one half.... Much quieter with plug in - bet that is the deciding factor over 1500 miles. Peter Quote Link to post Share on other sites
bnw Posted May 13, 2011 Author Report Share Posted May 13, 2011 The no load, free wheeling, plug out, makes the most sense with the pushrods removed. Least amount of stress on the motor. The noise, if there is any compression on #5 will be horrible. It's a 14mm hole. There should be some way to drill out a plug or drive out the center electrode and attach some type of baffle. At the same time filtering the air entering the combustion chamber. I fly out on Saturday, 21 May in the morning. Any suggestions? Quote Link to post Share on other sites
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