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Discussion Starter #1
Started overhaul a few days ago. 36236 miles from new. Original pistons, rings, valves. I lapped valves, refinished valve stem tips & adjusters & resealed tappet blocks at 12416 miles 7/4/14.

Motor rattled bad & odd knocking at top of cyl. I think carbon on pistons was hitting head?? I was shocked at the carbon build up. Started & ran fine. Used very little oil. Compression after the valve lap with .080" thick head gasket was 150 & 152# hot. Pre teardown compression test showed L 170, R 160. Obviously due to carbon as I now see. Will get full overhaul with sludge trap clean, 7.4 pistons, C630 guides, black diamond valves. All bearings, probably crank balance.

Here's photos of carbon...

Don
 

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Discussion Starter #3
Hi DU75389, No the 2nd time. I took off first time to reseal tappet blocks 12416 miles. So this time motor covered 23820 miles from then.

Crazy thing it still ran fine. Just the top end noise was so bad. I'll measure piston clearance etc when I get motor out of frame & in the workshop stand. I'm sure pistons are worn or collapsed. I'll see how bore is then too. I'm Hoping small end of rods are still ok. I'll have to get new rods if not. T140 rods are not bushed. I have no idea how long they usually last.
Don
 

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That is spectacular carbon Don. Quite a high mileage without a decoke i suppose. Last time i had the head off it had a fair bit of carbon but mostly soft due to the 2T oil i put in with the fuel. Of course, we have the higher octane fuel which runs much better here. Interesting to see the sludge trap which should be under half full judging by the amount i had in my crank used with no filter.
 

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Don, you could use that carbon to make some garden steps. The California fuel is certainly not very good for old bikes. I wonder what modern car and bike pistons look like.
 

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Discussion Starter #10
Hi All, I’m sure piston slap is very much part of the noises.
I’m going to to Torco TBO 40w for break in. Should it be winter I’ll consider 30w. I hope to be running in 4 months. I’m an optimist... or idiot?? I have little free time right now.
At work we saw very thin dark brown coating of carbon on motors that didn’t use oil. Customer was supposed to run premium 91. Some didn’t. Knock sensor backs off timing, but we saw cracked pistons. We had batch of burned valves from factory not machining seats concentric. So lots of heads off. I used to see lots of carbon in 90s from valve stem seals. Not quite this bad. Viton seals was cure.

I don’t know what rings yet. The oil ring will be 3 piece. That is pretty much settled.
Don
 

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Is this an argument for an octane additives, regardless of compression rating?

What would be the purpose/value of adding oil to the fuel? Would that not only make the engine smoke?
 

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Maybe my 2T oil i add to the fuel is doing some good. The carbon is always soft when i dismantle. Having used upper cylinder lubricants to all my old style engines since i was 17, i have never replaced valves, guides, or needed a rebore. On my current barrels, i have had new Harris rings but no noticeable bore wear yet.
 

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Discussion Starter #13
Hi, What part does pinging, pre detonation, light detonation which generates much heat have to play in this??? I don't know.

I can say I've tried every octane booster on the market in USA. None do any noticeable help other than Torco fuel accelerator. It indeed turns 91 into 100 octane. However pretty much needs to used at full mix ratio for 100. I found even small dilution from full strength results in ping. Brings $4.00 gallon fuel to $15+ gal. Then you have to bring several cans for all day ride.

Using 110 leaded race gas. Even 1 quart 91 per gallon of 110 will greatly lower the effective octane & bring on ping. The 110 leaded is off road use only in USA. It works fantastic!! Smells very different. Evaporates instantly like most modern fuels. Leaves decided grey residue down side of carb from tickler. I simply couldn't be happy riding with 100 mile leash. I wanted to do 300+ mile days. Only sold in my area in a few automotive speed shops. $15+ gallon. Could be way more now.

Only 3 places that sells California street legal 100 in San Francisco bay area I know of. None close to me anymore. $7+ gallon. It's not perfect, but works very good.
Don
 

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Hi Don,
Interesting pictures.
The machining on your cylinder head is terrible. The feed on the mill was much too fast for the tool tip diameter, the grooves are so deep they even left an impression in the head gasket.

Is the head flat? The gasket almost looks breached between the cylinders from the carbon build up between them.
The RH cylinder looks like it has been blowing into the exhaust side bolt, there is a lot of carbon in there, the inlet side looks clean.
It might be a trick of the camera but the gasket looks like it has had combustion gasses under it about half way across, you can see a-ring of discolouration around the bore, as though the metal has got very hot, there is a corresponding deposit of carbon on the cylinder head.
The valves don’t look pocketed. Yippee😊
Is the shiny edge on the RH Inlet valve evidence of contact, or is it just fuel washed.
The same with the RH piston outer edge showing metal, fuel wash or detonation- I suspect detonation has pinged the carbon off.
The high deposit build up when compared to cars, I suspect that it has something to do with the car engines running much cooler.
I would always get the crank balanced if it is out, the engine runs smoother for many years after the cost is forgotten😊

If I might be bold enough to suggest:

Koyo 3 piece roller timing side bearing from the late engine, to replace the weak standard ball bearing.

Inlet valve guides with machined groove for guide seals, even if you don’t fit them on this build, you might decide to try them later, then you have an easy option.

NOS Vandervell Tri Metal big end bearings, if you can find them.
I have heard that Clevite is making Tri Metal Bearings again, finally after 30 years of bi-metal only. Although I’m not sure that they make them our old engines.

regards
Peg.
 

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Look forward to your updates Don on this engine freshen up !!!

Col
 

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This is already a great thread!
Maybe Don, you can just remove the carbon and that'll take care of the noise. Put the head back on and away you go. However, might be a good idea to at least pull the cylinders off and check the pistons and the small end of the piston rods since you've gone this far. You've taken such good care of that engine that I'll bet that lower end is in pretty good condition considering the mileage.
 

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Discussion Starter #17
Hi Peg, The head was skimmed .009" back at about 4k miles when gasket blew across front center bolt eroding a groove in head. I know it was rough. Shop said they found the rough gripped head gasket better & reduced blowing. I used K&W Copper Cote in spray can. I stayed on top of head torque after that. No oil leaking at all. I did not remove or touch valves. Just cleaned carefully. I taped up ports & springs carefully durning machining. I didn't recheck flatness after head job, but cyl top was flat & undamaged.

At 12K mile interval exhaust tappet o-ring split & leaked oil fast. A cup per 1/2 mile! I couldn't believe it could leak that fast, but it did. I was only a mile from home. It started suddenly. Since motor was apart I decided to lap valves & refinish stem tips & adjuster screws. Very little metal removed during lap. The valves have always stayed in adjustment very well. Seldom needed any adjustment at all. I check head torque & valves 3-4k miles after this repair. Again valves just don't seem to change. I cleaned everything well. Rounded all sharp edges in combustion chamber, head gasket etc. Checking head I could pinch .0015" feeler gauge anywhere on head with straight edge. Same with cly top. Since I've got .00005 & .001" feelers, so can be more accurate. I have Starett 18" straight edge ground to .0005".

I installed the .080" thick head gasket to lower compression, which lowered from 170 to 150#. Huge improvement. This time used Mercedes sealant on head gasket. You can see a streak on head where it ran back as it stays soft where not pinched. Again no oil leaks at all. No compression coming up any head bolts. All 4 3/8 head studs have oil around them as I've seen 100% of these heads I've had off. This oil from around studs runs down as well as oil from front PRT. Rear PRT pulled loose at bottom & stayed on head. I got busy with life & stopped for a few days. I haven't removed head gasket from cly or checked head. I expect the valves are not pocketed due to they only had the light lap at 12k miles.

The clean intake valve is puzzling... I don't know why it's clean, other isn't. The absence of carbon in places is puzzling as well. The difference in carbon left & right is puzzling. The left piston top has always been this odd solid grey. The left plug always looks slightly leaner. The left intake guide is worn more than right. Why?? Back at 12K the left piston top looked pocked then also like detonation?? I really just don't know.

From new the pistons on cold start makes a little ringing bell sound. As you ride away you can hear it fade as motor warms. As miles racked up the ringing got louder & longer. Finally the clacking started as well as ringing. Maybe 24-25K miles. Slowly getting worse. Dealer said it was normal. Didn't matter. I bought new Dec. '73. Here in USA we had no idea of problems at factory. Pretty much everything was on back order at dealers. Had to call all around just to find clutch cable. Basically not aftermarket parts for 750 twins yet in mid 70s. Few Triumph dealers left, fewer new bikes on showroom floor. They sold out. I got last Tiger ever sold in my area so far as I could tell. They had 2 Bonnies left. Never again to see them. They dropped Triumph & just sold Honda then. Local dealer couldn't get new twins. They survived from repairs on older bikes. Still lots around. But mostly selling Suzuki. They sold well, but not like Hondas. Owner passed & shop closed. 2 miles from me. Very bad for getting parts. No internet then.

I'll clean up head & cyl top. I won't get motor out rest of way until next week. I'll need help. I get 2nd covid shot next Thursday. So laying low & no friends over until after shot. 1st shot threw me for a loop physically. So who knows this time. I'll pull cyl on bench as my motor lifting handle bolts to cyl top. So need to get motor out first.

I'll give detailed report on head, cyl flatness etc then. Will clean & look over valves & head.

I've thought about intake seals. I've never used them. I'll talk it over with Michael at machine shop. He's an older English gentleman. I believe he worked at Triumph Meriden back in the day. Very knowledgeable & skilled. He has machinist on staff as well. He's knowledgeable & skilled as well. I've only done original type work. Even then I really don't have true long term observation of several bikes. The old dealer guys learned a lot after 30 years in the shop.

I've thought of you & 3 piece main every time I ride. I'll get back to you when I get crank out. Got too much on my plate with real life & getting cyl, head work done at this time.

I'm 100% & them some going to use 7.4 Harris pistons. They have proven to work so well. After a 200 mile road test on '73 Bonnie in every type riding condition I am 100% convinced how well it makes bike run on California fuel. I wager you cannot feel power loss with 91 fuel.

Back to crank, I need to get new pistons & weigh them. Compare to what I had. Study & pray... for best balance factor.
I'll looking to find factory balance tool & weights. See what factory did. Then pay for balance check, just to see where dynamic is currently. Only then will I have crank dynamic balanced. This means several 100 mile trips to different shops. My fear is shop will say we'll balance to your factor, then they do what they like....

Peg, do you have figures or print out of factor you used with what weights?

Shop manual states 85%. Triumph factory prepping T140 for racing booklet states 85%. Some say T140 type crank is lower 74 or 76%, But what is weights of parts?? Does a light piston want same factor as heavier piston?

I did 2 "farewell" rides first of nearly 90 miles, 2nd of 55 miles. Different speeds up to 75mph. Felt power different speeds, flat & on hills. Attempted to memorize how each felt & vibration of each condition. Really very comfortable regarding vibration up to 62mph. Then vibration comes on 64 is worst. Faster it begins turning into a buzz. At 70+ it feels like an old Honda 305. Just a buzz. More comfortable than 65, but not very comfortable. I generally ride 62 on freeway, faster when needed to keep up with traffic. 70 motor pulls very easily & freely. Trending downhill or tail wind of course vibration is less. 70 feels better then, 65 is just a rough place. Tach tends to increase in error as rpm increases. 70 mph reads 5-5200. But... after some hours riding non stop it will go close to correct. Stay correct for many miles. If you stop motor, it reverts back to error. Can't figure that one out... So I go by MPH & calculate rpm. But 2-3000 is pretty close all the time. Again I can't figure that out. Measuring axle center to street sitting on bike, doing math, workshop manual figures are very close. Odometer is nearly spot on in the odometer test miles & with google maps over 100 mile highway ride on same straight highway.

So I have lots of puzzles & mysteries. The main bearings sound ok, but timing gears whine some cold. Much quieter hot. At least I think timing gears?? Or is it right main bearing?? Listening with ear, screw driver, stethoscope, bearing sounds quiet. All bearings will get replaced. High gear bearing is early version.... I'd think as trans has never been apart. If I can get new, I will. If gear race is worn I'll have to get high gear set I guess. If it's perfect it will stay. Always kept fresh trans oil in it.

I hope no bearings loose on crank or in case... One never knows until you teardown.

I hope to not grind crank. I checked oil pressure smoking hot recently in preparation for tear down. Was very good hot idle. So pump & clearance should be good.

Last 2 sets of Hepolite shells I was involved with had .00025. .0005 more clearance than old bearing removed! This is putting clearance near .002". I want .00125 to .0015" if possible. I've been looking at inserts. Cleavite is recommended by some. Federal Mogal by others. I have no clue. NOS would be ideal. They are long gone. I'm all ears for best bearings. I'll plastigauge old bearings to verify clearance & use same stick of plastigauge for new bearings. If I have to buy double on parts so be it. I'd rather not compromise. Rod small ends?? If worn, which new rods?? I don't want to increase vibration. I don't use high rpm.

Thanks for the patience with 3 piece main bearing. I'll most certainly get back to you on this.
Don
 

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Discussion Starter #18
Hi Gary, I was looking at bore very closely this morning. Honing is 100% gone in upper ring area. I can see witness marks on walls where rings reverse direction as piston rises & falls. I can see a small ring of original honing above the top ring run.

You know how in the old days, you get worn American car motors with a ridge. Get a ridge reamer & cut it out. Then push piston up & out. Hone cylinder. Get new rings. Grant seemed to work best on worn bores, followed by Hastings. TRW was my favorite on rebores. It worked. We seldom measured bores. Just check ring gap. Actually had high success rate.

I find for some reason Triumphs are different. They don't get the deep ring ridge wear. Maybe because lower miles on bores before overhaul?? I found the cars would be successful with surprising amounts of taper & out of round. But Triumphs seem rather sensitive to taper & out of round. Maybe it's because bore is smaller?? I don't know.

Looking at my bores, you'd think you could hone & ring them, It'd be fine. However I've seen so many failures doing so. I'll have detailed measurements by next week.

I'm committed to lower compression pistons. I'll go .020 over 7.4. If bore wear proves too much, I'll go .040 over 7.4. I have too much bad experience with Triumphs to re ring this motor.

One problem is so many of the failures owners did not use break in oil.... Now we have 2 problems to think about. I don't know why there is such resistance to use break in oil.

One thing I've seen is these motors seem to work their hearts out. They don't seem to last long. I felt getting 36k on original motor was pretty good. Modern bikes often go over 100000 miles.

I'd like to hear from old Triumph dealer mechanics & hear how long the average Triumph Twin lasted between overhauls.
Don
 

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Did the machinist use a plough, you could sow agriculture in those furrows?

I look forward to your progress, Don. Will be an interesting read. Be careful not to let it turn into an oil thread.
 

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Don, just wondering, did you occasionally run the engine at full throttle throught the gears at 6000 rpm to let's say 70 mph?
 
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