Seizure?

[Shark]

Went for a ride today ( two up ) and did about 20k's with no problems, pointed it at a fairly steep hill ( 2nd gear for about 1k at 3000 rpm steady throttle ) got to the top ok but soon thereafter it lacked throttle response and pinging badly so I backed off and was in third doing about 60k's and the back wheel locked up so I pulled the clutch and rolled to a stop. It was smokey and crackling as if it were rather hot, so I let it cool for 15 minutes or so and started first kick and got home with no further problems. Plugs looked normal and it was not smoking or crackling when I got home. Suggestions/advice appreciated. ( 61 super rocket )

[Triton Thrasher]

Steady throttle how far open?

3000rpm uphill with a passenger could be labouring it a bit.

How many miles since last rebore?  I'd suspect a too-tight bore if it's recent.  Otherwise a weak mixture on slide cutaway or needle clip position.

You may as well take the barrel off to look for stuck rings now.

[Shark]

Thanks for the quick reply TT, it was about half throttle and not pinging at the start of the hill. Don't know when it was last rebored, the guy I got it from told me he lifted the barrel for a look and the piston to bore was .004 so he honed it lightly and fitted new rings and put it back together, that was about 500k's ago. It has a new monobloc with clip at #2 and #3 cutaway. When it cools right down I will stick a camera down the plug hole and see if there is anything untoward. If it looks ok I will ride it again tomorrow and do a compression check. Thanks again.

[muskrat]

G'day Shark.
I'd agree with TT, she's a bit lean. The timing could be a tad advanced as well. Lift the needle a notch.
What grade of fuel are you using?
Cheers

[Triton Thrasher]

At the same speed in a lower gear, it might have been noisy and shakey, but it probably wouldn't have seized.

[A10Boy]

I wouldn't strip it down yet, put a few miles on it and see if it smokes or uses oil. It'll probably loosen up.

[RichardL]

I wouldn't strip it down yet, put a few miles on it and see if it smokes or uses oil. It'll probably loosen up.

Based on the possibility of bores too small and pistons seizing as the result of high heat, would one really want to test that diagnosis by waiting for another seizure, which might have more serious results? Also, I don't envision the pistons wearing down to size to fit undersized bores while leaving the pistons and bores in decent condition.

As always, open for chastisement if I have spoken right out of my hat. I'm sure someone will correct me about something, as usual.

Richard L.

 

[Shark]

Musky, am running 95 so can drain that and try 98 and if no joy will then go timing and needle.
TT, agreed,
A10Boy, will ride it again today ( after changing to 98 ) and take it from there, fingers crossed as the sinking fund has gone on another machine.
RichardL, it is a dilemma in that I don't want to open it up unless I really must do so but by the same token the old " stitch in time saves nine" keeps bouncing around in my empty head.
Thanks for the advice will keep you informed.

[beezermacc]

Sounds just like a problem we had with a mate's engine after complete rebuild, going up hill the bike lost power and stopped. It restarted straight away but didn't feel right. I had a go on the bike and opened her up on a flat bit of road and eventually it lost power and stopped with no compression. Strip down showed both exhaust valves temporarily seized due to heat. The problem was caused by over-retarded timing which caused too much heat. The pinging is normally associated with over-advanced timing but on this occasion it was just too hot. The lesson....whilst it is advisable to retard the timing to accommodate today's crappy fuel, don't overdo it! I now find, with an iron head, I set the timing according to original spec and I don't have any problems. Of course, if it does ping a bit, you can always retard it a bit. I always use the best fuel available and lead substitute.

[The Artful Bodger]

I had the same sort of problem as Beezermacc describes with my Huntmaster when I first put it back together. Pinking (pinging) every time under even a slight load with the standard ignition timing, I retarded the timing twice to try to cure it and although the pinking lessened the engine was getting very hot and still pinked every hill even solo. Oil leaking and a real hot smell, terrible when two up.
  Out of desperation I found a garage selling leaded 4 star petrol for classics..... at a price! I filled up and two miles down the road the bike totally changed, I couldn't get it to pink no matter how much load I put it under. I re-set the timing to standard and it went like a train, no pinking, no hot smell and no (well almost) more oil leaking.
  I truly feared the engine seizing before this but just the change in petrol was a magical "cure all". I've read many posts on modern fuels and many people seem to have no problems, not so in my case. Some research led me to "Millers VSP" fuel additive, this is an octane booster, lead replacement and ethanol proofer.
  Using premium unleaded (BP Ultimate) and the Millers the bike runs the same as using the leaded 4 star but at a much lower price. I have never had any pinking or overheating issues since ( several years now).
  Retarded ignition will make the engine run very hot, I often use my M21 for commuting to work coming home in the early hours of the morning through a forest, so dark. I set the timing and it was fine for a short while, then early one morning I looked down to see my exhaust header glowing bright red, I do mean bright red!
 I checked the timing the next day to to find it about half way between where it should have been and TDC. A crack in the timing gear allowed it to slip. Even this old thumper gets BP Ultimate and Millers VSP, all my bikes do and I have peace of mind riding them.
Colin

[muskrat]

A few years ago the '51 A7 nipped up (chasing a G15CSR at 80mph). Polished the rough spots of the piston, gave the bore a quick hone, new rings. Put the bad piston in the good bore and the good piston in the bade bore. Haven't had to look at it since.
I use BP 98 and add Nulon pro strength octane boost in all my bikes (even the lawn mower).
Cheers

[Rocket Racer]

I agree with what everyone else has suggested, bad fuel can be a real bugger.
Another avenue is you mentioned spending quite a while in second and third; now those gears put a lot more load on the box than top does and its quite feasible you seized a gearbox bush. -Your sleeve gear and mainshaft is not spinning at the same speeds unless in top and the loads are travelling up the layshaft and coming back via the sleeve gear.
Early roadtests often talked about boxes tightening up (as inadequate running in), but this would be unusual for a well used box with oil in it.
So I'm going out on a limb with that idea.

Not sure where in the continent you are but your region can also be a factor. I lived in Queensland for a while and my OIF lightning hated the heat.
But stick to the highest octane you can get with a super rocket.

[Shark]

Thanks for all the comments gentlemen, I have had a look down the plug holes and could not see anything sinister, no carbon build up on the pistons at all ( stamped numbers legible ) and the bores not gouged. I have octane booster and will run 98, got tomorrow off but I bet it rains all day.I will keep you informed and thanks again.

[Shark]

Well tomorrow took its time in coming!!! I have just taken it for a 50k ride with a few long and steep hills and it ran as it should , pulled very well up the hills with no hesitation and was still accelerating at 130k's on the flat. I have taken Musky's tip and gone 98 with octane booster and will not push it quite so hard two up (thanks TT). Thanks to all those that replied. Cheers.

[East_Coast_BSA]

Never cared for Octane booster and refuse to use it.  The basic problem is it reacts differently every time.  Since fuel blending is like buying cans of paint (the colors are NEVER exactly the same from can to can), octane booster works better or worst depending on the particular blend of fuel.  Even the same grade from the same gas station can vary from delivery to delivery.  It's just too inconsistent in performance and leaves too much to chance.  Lucky for me, my 59' runs fine on 93 octane (with the 10% ethanol).  I keep the jetting on the fat side, which also keeps the "blue" out of the pipes.  The bike is stock timing, .040" flat-tops and never pings.  Maybe I'm just lucky.