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Discussion Starter #21
Are you measuring piston to bore clearance at the right part of the piston?

Perpendicular to the pin, a little distance up from the bottom edge of the skirt.
Yep, approximately 3/8" from the bottom of the skirts.

I'm now puzzled, those bore dimensions are standard size Morgo, so have not been rebored. On the piston clearances you have, things would have to be really hot for the pistons to tighten, as it appears they have. What fuel were you using? The "standard" compression ratio with a 0.039" head gasket is 9.5:1, very high indeed for US fuels
I almost exclusively run 100LL AVGAS, or 100 sunoco unleaded from a local station. Though with 9.5:1 when it was a 650 I never had any preignition issues even with standard 93 octane.

Unless the pistons were overly tapered to begin with. Perhaps poor ring bedding and loose clearance prevented adequate heat transfer. I'm at a loss.
 

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Yep, approximately 3/8" from the bottom of the skirts.


I almost exclusively run 100LL AVGAS, or 100 sunoco unleaded from a local station. Though with 9.5:1 when it was a 650 I never had any preignition issues even with standard 93 octane.

Unless the pistons were overly tapered to begin with. Perhaps poor ring bedding and loose clearance prevented adequate heat transfer. I'm at a loss.
I'm not really seeing wear on the lower skirt perpendicular to the pin, where you were measuring, and if the cross-hatching is still visible, it's hard do see where the clearance could have gone from 0.005" to around 0.011+. Maybe you can see it! I really would send the gist of this to Morgo and see what they say - it beats me too.
HTH
 

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Hi BMF, I'm high jacking thread. I didn't go with anything yet. I just started taking motor out today. Full overhaul. The shop said they would not install manganese bronze as they felt they wore out too quickly.

I could install & ream manganese on my own & cut seats with Neway cutters. I really considered that. But I want maximum service life, so I'll go with C630.

They recommend 3 piece oil rings. Generally Hastings or Grant, 3 piece. I didn't know they made Triumph 3 piece sets. I was leaning towards Riken from MAP Cycles. I will use what they recommend. They & me are on same page. I want longest service life, performance be what it may. They do what customer wants. They can do very high performance if that's what you desire. I like to ride long distances so that's what I hope to achieve. I expect that will happen. Best part is they are only about 50 miles from me, so I don't need to ship anything. Gas will be be less than shipping.

I covered 36232 miles on original pistons, rings, valves, guides. I resurfaced valve stem tips, adjuster screw tips & lapped valves at 12k miles when I did tappet block reseal. Didn't hone or tough rings. Valves, pistons rattle like mad. I don't hear main bearing noise, but... Pistons rattle so loud, it may mask other noises. Doesn't use oil & runs great. Who knows what real cause of noises are from. On 100f+ day when working hard fully heat soaked motor is it's quietest. So I'm thinking piston rattles?? Valve clearance is good. Who knows what I'll find on tear down?? I learned long time ago, tear down is often full of surprises... Leave no stone unturned during inspection. Maybe rod small ends are worn? Big ends good. Oil pressure near 35# at idle heat soaked. 70#+ 3000. But... who knows? Plastigauge will tell.

I'm far from rich, but I don't have a dollar limit for overhaul. At least not yet... I'll only sublet what I can't do.

If I could get Genuine NOS Triumph rings +.020, I'd be inclined to use them. Sure have worked well for me so far. I ran my '70 TR6C 30k miles, never a teardown. Not even clutch replace. Like an idiot sold it. Best bike I ever owned. Mostly commute miles though.

Balance factor... that's another question. I'll compare weight of new
Don
 

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Discussion Starter #24
I'm not really seeing wear on the lower skirt perpendicular to the pin, where you were measuring, and if the cross-hatching is still visible, it's hard do see where the clearance could have gone from 0.005" to around 0.011+. Maybe you can see it! I really would send the gist of this to Morgo and see what they say - it beats me too.
HTH
Well my conclusion after talking with some people is that the pistons have a messed up profile. That’s the only way we could explain the wear ring below the ring grooves. So, even though the bore seems ok, I’m going to bore .020 over and use a good set of pistons (probably MAP billets)
 

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Well my conclusion after talking with some people is that the pistons have a messed up profile. That’s the only way we could explain the wear ring below the ring grooves. So, even though the bore seems ok, I’m going to bore .020 over and use a good set of pistons (probably MAP billets)
Make sure that the MAP's have the correct gudgeon (wrist) pin height, the pistons for big bore kits are for long rod engines, the T140 short rod pistons will be the wrong height. Also the crown profile is different, the T140 head has a chamfer to clear the piston, the 650 head does not. Been there, done all that!
HTH
 

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I just had a look at the MAP big bore pistons, things of great beauty! You can spec these at 76mm a la Aerco and bore to that
 

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Discussion Starter #27
They are pretty. As I’m sure you saw, they have them for aftermarket big bores. For what they are, not too horribly priced since they come with a decent ring set.

Im still a bit conflicted though. Should I bore these, or buy a UK reproduction 650 barrel and go with std JCC pistons and good rings.

Decisions.
 

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i am somewhat bemused about the morgo pistons. i put one on 30 somethibf years ago and its been fine evee since
 

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Discussion Starter #30
The pistons 30 years ago may have been from a different manufacturer. I’m guessing that the pistons were tight up top, and likely were damaged in the first few minutes of running. In my experience, detonation eroded the piston around the top ring groove, and leaves black death galling marks on the thrust faces. I guess I’ll never really know for sure. Timing was dead nuts on when I put it together, and I haven’t touched it since. I don’t have any evidence to blame Morgo. In the end it was my responsibility.

I have the time right now, so I may pull the crank and clean The crap trap. It’s been many miles and moons since I did that. Maybe.
 

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The pistons 30 years ago may have been from a different manufacturer. I’m guessing that the pistons were tight up top, and likely were damaged in the first few minutes of running. In my experience, detonation eroded the piston around the top ring groove, and leaves black death galling marks on the thrust faces. I guess I’ll never really know for sure. Timing was dead nuts on when I put it together, and I haven’t touched it since. I don’t have any evidence to blame Morgo. In the end it was my responsibility.

I have the time right now, so I may pull the crank and clean The crap trap. It’s been many miles and moons since I did that. Maybe.
You’re just trying to have too much fun!
 

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I'd agree that there is something else wrong, be it ignition timing or whatever - those piston got HOT.
i hope that's the only issue, because it means it's fixable at our end.

The pistons 30 years ago may have been from a different manufacturer.
that's the question. im sure i have mentioned this before, but these guys are maintaining a very small industry supplying an ever-decreasing market. 30 years back the stuff was profitable. now that everybody who has a 650 and wants a morgo has one, th e market is much smaller and is likelier to see QC problems

such is the way of the world
 
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