[thefledgling]

First off, I know I could remove head to check. That's for me a lot of work. Tank, rockers, exhausts, removed too. Head gasket replaced, several retorques and setting valves. Add to that, if it is curved, removing valves, going to a machine shop. Then all reassembled. I'm, tbh, losing interest. I get one ride in then next ride something else 'occurs'.

1000 miles ago I replaced the composite head gasket with a new composite. (At the same time I fitted new rings and honed the unworn standard bore cylinders.)

I didn't check the head was flat when I did that, I'm fairly certain. It seemed the gasket was leaking between cylinders. Since then, I've retorqued several times at appropriate intervals. And meticulously ran-in new rings.

The bike has run extremely well since the new gasket and rings. (baring the other unrelated issues that arise). Plenty of power, easily go up to a speed I feel too fast, 90mph, with more to come. Great acceleration, with engine sounding sweet at idle and a nice crack when revving up the dial.

Three weeks ago did 130 miles round trip, with long stop at destination. Warm day, not hot, never stuck in traffic, no worries engine overheating. Stopped couple of times home for few minutes . Engine started hot great, tickled of course.

Got home. Cup of tea, etc. Maybe an hour later, maybe less, decided to do trip to shop. Engine had a little warmth still, not much at all.

Can't remember if it started well, but as soon as I took off engine sounded rough, and had little power. Probably ride half a mile, then turned round and headed home. No improvement during this time.

Bike idled fine, getting home. Walking to back of bike, could hear cracks in the exhaust note. Seemed equal both pipes. Revving engine made this cracking louder, as of course the general exhaust volume increased.

I retorqued head. Checked for air leaks at carb manifolds. Taps give very good flow. No debris in carbs. Not electrical I'd guess, problem isn't sporadic, cylinders are firing. E.I. fairly new. No ancient wiring.

Something happened in that hour the engine cooled. I'd guess the cylinder head contracted, and now there's a leak at gasket.

I've checked compression. Is a bit less, equal on both cylinders. Oil in cylinder didn't increase compression. However, I'm not confident my guage reads well, has always shown low compression even when obvious engine is okay. I have no compressed air supply, so can't do any leak down tests.

However, seems very likely it's a leak between the cylinders.

Is it know for a composite gasket to fail so soon, all else being okay?

When I replaced head, used same thickness PRT seals. Gap before compression was about same again as gasket, i e., 1mm.

I don't see the carbs playing up in that hour. They were thoroughly cleaned several times a thousand miles ago. I use nearly always ethenol-free fuel, although didn't on last trip. Fuel is fresh, worked normally on long trip. I've been getting 60+ mpg.

Checked carbs. Washers at base of springs flat in slider. Fat o-rings ok. Crossover hose okay and recently replaced.

 

[Flicker]

Fledge have you checked your ignition timing with a strobe?

 

[thefledgling]

Fledge have you checked your ignition timing with a strobe?

No. Could do. But this happened in the hour bike was stationary, cooling down.

Checked valves btw, reset then completely, and that pushrods are seated.

Also had rocker boxes off. All okay inside. Everything in place, plenty of oil everywhere.

 

[slofut]

No. Could do. But this happened in the hour bike was stationary, cooling down.

Checked valves btw, reset then completely, and that pushrods are seated.

Also had rocker boxes off. All okay inside. Everything in place, plenty of oil everywhere.

Don't assume anything fledge, in troubleshooting it will cost you time and frustration. I'm never surprised with anything electronic. Check and document the easy data first before tearing into the motor. Above all don't guess and throw parts at it. If it's ign timing that would be easy.

 

[DMadigan]

Presumably; you know not to machine the head flat if it is warped?

 

[thefledgling]

Presumably; you know not to machine the head flat if it is warped?

I've read better to bend straight.

Skimming seems a start of another nightmare. Special sized PRT seals, thicker gaskets, both miraculously the right extra thickness. And, if skimmed and rebends, more skimming?

That's partly why I didn't check it was flat. That's my excuse, and I'm sticking to it. I've no idea where I'd get a head straightened either.

 

[Flicker]

I've been to a few motorcycle shops in my area and asked them if they could do this or that to my old bikes and I get the blank stare.
That blank stare is the most dangerous stare, so I thank them politely and head out the door
Then my only option is to fix these bikes myself. I'm a competent mechanic but there are nuances galore to learn about each type of machine.
For example, not skimming the head: didn't know that.
I just assumed that over there in your neck of the woods there would be a service network that we don't have.

 

[slofut]

Flicker, i just sent my complete top end to Frank Deihl Classic Cycles in SC. Ive heard that name in good standing with Triumphs as long as i can remember and when I asked Bonneville Shop for referral to a good head shop thats where they sent me. Talking with Frank he indicated that they would straighten the head before any skimming. I feel good about them having my parts and will post back with results. They received my parts yesterday.
I sent the barrels with guide blocks, prt’s, old head gasket, pistons with rings in bores and head all bolted together so they would have indicators to go with any wear measurements. Hoping ill get back a bolt on assembly in a few weeks and be riding soon.

 

[Adam M.]

Check your ign. timing before doing anything to the engine. Check your spark, spark plugs and their wires, all the connections between them and their connection to the coils. Had exactly the same problem with my BSA - a culprit was a wire sitting quite loose in the coil. Check your low voltage wires between ignition and the coils with their connections being tight. Don't remember do you have points in this bike, but if you have them check if they are clean ( piece of paper moved between closed points will show it ) and if they have a proper clearance when open.
Bent cylinder head is only a theory, and never happened to me or my circle of friends on a bike during use. If your cyl head was bent, you would have problems from a start of using this bike. Besides, small leak from a head gasket never affected my engine severely, like yours - I know, I had one as well.

 

[thefledgling]

Flicker, i just sent my complete top end to Frank Deihl Classic Cycles in SC. ...they would straighten the head before any skimming...
I sent the barrels with guide blocks, prt’s, old head gasket, pistons with rings in bores and head all bolted together so they would have indicators to go with any wear measurements.

Sounds good. But yikes. A lot of taking stuff of. A lot of work. Postage cost must be high.

I've got a project bike on the go. It should run 🤣 when I one day finish. Top end never opened, only 3,000 miles on it. There'll be all new custom electrics by me, so no problems there🤣😂. And just about everything else new, or refurbished by, yep, me 😂🤣😆.

It's never ending with present bike, and stops me progressing with project.

I've just took the bike for a 'run'. Just a few yards. Very, very lumpy, at idle and running higher revs. Struggle to get above 4,000 revs, sounds so awful, so strobing isn't the answer, don't want to damage anything. The outer timing plate is still in correct position, I'll get the TDC tool and check static timing. If static timing is correct, that's it, really, it's the head.

A carb bowl thread stripped, now leaking. Didn't do it up tight, just one time too many I'd say. Another day, another problem.

 

[thefledgling]

If your cyl head was bent, you would have problems from a start of using this bike. Besides, small leak from a head gasket never affected my engine severely, like yours - I know, I had one as well.

That's really what I was as asking in a vague way. Would the gasket almost immediately leaked? Or rather, could it settle okay, but eventually 1,000 miles later succumb to any curvature?

I'll check the electrics another day, spent allocated time on it today, thanks.

 

[Flicker]

I think what we're all saying in a vague way is that it probably is not the head gasket given they symptoms and tests you've described
The one test you did not mention was ignition and that can easily make the engine sound like it is coming unglued
Timing, intermittent connections, componentry, etc.
Somebody once said 90% of carburetter problems are electrical and whoever it was deserves a medal
Now I'm sure somebody way more qualified to give advice than me will be along shortly so hang in there

 

[thefledgling]

Vague's the new... something...

 

[Flicker]

Flicker, i just sent my complete top end to Frank Deihl Classic Cycles in SC. Ive heard that name in good standing with Triumphs as long as i can remember and when I asked Bonneville Shop for referral to a good head shop thats where they sent me. Talking with Frank he indicated that they would straighten the head before any skimming. I feel good about them having my parts and will post back with results. They received my parts yesterday.
I sent the barrels with guide blocks, prt’s, old head gasket, pistons with rings in bores and head all bolted together so they would have indicators to go with any wear measurements. Hoping ill get back a bolt on assembly in a few weeks and be riding soon.

Slofut, I'm glad you got that resolved and it's a good name for me to remember.
I'm doing a top end on my 72 Daytona now and all the parts and services I had to chase around took a significant amount of time and money
To have somebody just take the whole bundle and make it right is probably well worth whatever they charge
Never occurred to me that I could just ship it somewhere instead of casting about for service providers locally
Thanks for the tip!

 

[rambo]

A low voltage battery will often make electronic ignition go to full advance. Especially Boyer.

 

[thefledgling]

Full charged kept. 12.7v. This happened after a 130 miles run in daylight. I have a handlebars voltmeter, bike charges from 2100 revs. Three phase alternator.
Couple weeks before this problem, I accidentally parked and left my two eagle-eye running lights on for several hours! Bike fired on first kick. Wassel.

 

[slofut]

Slofut, I'm glad you got that resolved and it's a good name for me to remember.
I'm doing a top end on my 72 Daytona now and all the parts and services I had to chase around took a significant amount of time and money
To have somebody just take the whole bundle and make it right is probably well worth whatever they charge
Never occurred to me that I could just ship it somewhere instead of casting about for service providers locally
Thanks for the tip!

Yea ive learned that at this point i have more money than time, and it aint because i have a lot of money. 😅 Ive always thought i had to do everything myself, but as many projects as i have its best to farm out all i can.

 

[rambo]

Full charged kept. 12.7v. This happened after a 130 miles run in daylight. I have a handlebars voltmeter, bike charges from 2100 revs. Three phase alternator.
Couple weeks before this problem, I accidentally parked and left my two eagle-eye running lights on for several hours! Bike fired on first kick. Wassel.

It is most likely that gasket again.

 

[Snakeoil]

Personally, I prefer a copper head gasket. If your head is curved, my guess is the pushrod tube set up was wrong and the head was bent during the torquing process by your or a previous owner. Failure to check flatness cannot be justified regardless of the reasons. Others are being nice. You need a good kick in the pants for that move. The heads are relatively soft, hence the ease of bending them and I have seen threads, probably hear or maybe on YouTube (to long ago to remember exactly) on how to straighten them. Personally, I would think that if you can bend them with the head bolts, you can straighten them with the head bolts. If this were my problem, first, I'd get a new copper gasket and then I'd try torquing the center bolts first and then work to the outside and see how that works out. You really have nothing to lose. A couple of heat cycles and your problem may be fixed.

 

[HayMike]

Plugs, wires, connections, look at the spark. If it's good, check the carbs. I don't think the gasket goes bad sitting.