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Old 08-14-2014, 03:16 AM   #1
jdizon
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Default T120R Engine Build - Sanity Check

Engine Gurus,

Please review my engine build/parts list.

Primary Use: Sunday City ripper for mostly riding around town.

Frame
==============
Frame: Custom Rigid
Wheels: Front/Rear 19,18
Drive Sprocket: 19
Wheel Sprocket: 43

Bottom End ( 1968 T120R Base )
==============
Cams: Megacycle 510-05
Tappet Inlet: "R" PN# 70-3059 R
Tappet Exhaust: "R" PN# 70-8801
Timing Gears: Lightened
Oil pump: Morgo High output
Conn Rods: Map Cycle 6.5" H Beam 4340 steel Part # MAP7061
Crank Balance Factor: 85%
Stator: Wassell 200 watt high output.

Top End
==============
Cylinder: 750 Big bore kit, Triples Rule All alloy Aluminum block with Nikasil plating + Total Seal gapless rings.
Cylinder Head: TR6 single intake with 3 angle valve job
Valve Spring : R/D 506-T kit
Carb: Single Amal 932 Premium with 3.5" slides
Exhaust: High left side exhuast 1-1/2"
Ignition: Ard Timing cover with Morris Magneto (lytedrive)

Transmission
==============
Beltdrive: TBD

Misc
==========
Crank Case breather located to front motor mount.

Picture of the roller engine is going in.


Last edited by jdizon; 08-20-2014 at 02:11 PM.
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Old 08-14-2014, 03:51 AM   #2
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Default Re: T120R Engine Build - Sanity Check

I'd give the lightened timing gears a miss,and even go for the heavier T140 gears if possible. You'll lose power with lightened gears, but it can improve acceleration at low speeds.
The Morgo pump is the same capacity as the '69-onward Triumph pump, and a good replacement if your old pump is worn.

I'd do some intake port work and make the ports square (with about 6mm radius in the corners of the square), just near the valve guide beside the inner 3/8" bolt hole. The rest of the port is more than big enough. It's optional, and will only count at high rpm.

If your points and AAU are no good, I'd go straight to electronic ignition. You'll still have an advance curve that way (less chance of melting pistons from detonation). Magneto will just give you a weaker spark at start up, with no real benefit.
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Old 08-14-2014, 09:00 AM   #3
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Default Re: T120R Engine Build - Sanity Check

that sure seems like a whole lot of go-fast money being put into a motor......with a single carb head.

IMO, for a street bike...

I feel it's wrong to build a motor that is designed to make most of it's power at high rpm and gives up it's low end torque.

most of your riding around town will be below 4000 rpm.
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Old 08-14-2014, 10:17 AM   #4
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Default Re: T120R Engine Build - Sanity Check

Man,that's a 6000 buck engine build ....And probably a crankshaft breaker if you use all the performance...
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Old 08-14-2014, 10:38 AM   #5
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Default Re: T120R Engine Build - Sanity Check

He's in tech, he has a lot of spare cash ;P
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Old 08-14-2014, 10:52 AM   #6
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Default Re: T120R Engine Build - Sanity Check

Quote:
Originally Posted by Truckedup View Post
Man,that's a 6000 buck engine build ....And probably a crankshaft breaker if you use all the performance...
I agree,

typically an expensive full race built antiquated design motor, just makes for an expensive unreliable street motor.


you want a pretty fast reliable old Triumph motorcycle, just do a well built stock motor.

you want to go really fast on a motorcycle ...put that $6K down on a BMW 1000 R/R
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Last edited by Tony the torch; 08-14-2014 at 12:43 PM.
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Old 08-14-2014, 12:55 PM   #7
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Default Re: T120R Engine Build - Sanity Check

I'm not opposed to going back to a dual carb setup, I just preferred the the aesthetics and simplicity of a single carb and tuning. I also thought that performance degraded with a single carb in the Higher RPM/Top end range?

In terms of the cam, This is the mildest cam in the megacycle product line that is similar to the 3134 profile cam. From the specs, best performance can be seen at low to mid range. For my understanding, Where am I sacrificing low end torque?

Appreciate your feedback.

Quote:
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I feel it's wrong to build a motor that is designed to make most of it's power at high rpm and gives up it's low end torque.

most of your riding around town will be below 4000 rpm.
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Old 08-14-2014, 03:13 PM   #8
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Default Re: T120R Engine Build - Sanity Check

If you are doing all of that, why not go with a short rod 750? It's a much better set up.
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Old 08-14-2014, 03:34 PM   #9
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Default Re: T120R Engine Build - Sanity Check

Already purchased the Big Bore kit. What is required to work with it? What do you recommend?

Quote:
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If you are doing all of that, why not go with a short rod 750? It's a much better set up.
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Old 08-14-2014, 04:01 PM   #10
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Default Re: T120R Engine Build - Sanity Check

Quote:
Originally Posted by jdizon View Post
Already purchased the Big Bore kit. What is required to work with it? What do you recommend?
My opinion...The big bore kit will go nicely with the stock "3134" cams. Spend your money on a good electronic ignition,new carbs, good valve work , balancing and a proper exhaust...Then spend a few hundred on dyno time to get it sorted out.
The engine will make great power from 3000-6000 rpm and you'll be able to run 4.5 ish overall gearing so it won't be a paint mixer when you go fast...
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Old 08-14-2014, 04:02 PM   #11
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Default Re: T120R Engine Build - Sanity Check

750 rods, and the regular 750 cylinders, it's what Triumph went with in '73 ish. The issue with the 750 "big bore" is that the piston speed is too high, so the shorter rods slow that down. I have also noticed no real difference between a 650 and a 750 with a big bore, but have noticed a difference between a 650 and a short rod 750. This could just be my imagination, since I haven't dyno'd either one.
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Old 08-14-2014, 04:24 PM   #12
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Default Re: T120R Engine Build - Sanity Check

The cam # I found in my engine was the "K" 3134, Not sure if it's a particular one I'm looking for? I recall the one to get was the cam from a 1970 which I believe is the Q?

Quote:
Originally Posted by Truckedup View Post
My opinion...The big bore kit will go nicely with the stock "3134" cams. Spend your money on a good electronic ignition,new carbs, good valve work , balancing and a proper exhaust...Then spend a few hundred on dyno time to get it sorted out.
The engine will make great power from 3000-6000 rpm and you'll be able to run 4.5 ish overall gearing so it won't be a paint mixer when you go fast...
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Old 08-14-2014, 04:25 PM   #13
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Default Re: T120R Engine Build - Sanity Check

Thanks for the info. I've already purchased the big bore kit so I guess I need to find that noticeable gain in other upgrades.

Quote:
Originally Posted by HCC View Post
750 rods, and the regular 750 cylinders, it's what Triumph went with in '73 ish. The issue with the 750 "big bore" is that the piston speed is too high, so the shorter rods slow that down. I have also noticed no real difference between a 650 and a 750 with a big bore, but have noticed a difference between a 650 and a short rod 750. This could just be my imagination, since I haven't dyno'd either one.
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Old 08-14-2014, 05:05 PM   #14
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Default Re: T120R Engine Build - Sanity Check

Quote:
Originally Posted by HCC View Post
750 rods, and the regular 750 cylinders, it's what Triumph went with in '73 ish. The issue with the 750 "big bore" is that the piston speed is too high, so the shorter rods slow that down. I have also noticed no real difference between a 650 and a 750 with a big bore, but have noticed a difference between a 650 and a short rod 750. This could just be my imagination, since I haven't dyno'd either one.
Shorter rods do not change piston speed
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Old 08-14-2014, 07:16 PM   #15
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Default Re: T120R Engine Build - Sanity Check

Quote:
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Shorter rods do not change piston speed
With a shorter rod, piston speed will be slightly higher near the top of the stroke and slightly less toward BDC. Not much in it.
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Old 08-15-2014, 05:04 AM   #16
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Default Re: T120R Engine Build - Sanity Check

Hey man, I have had the same bike 30 yrs. A 68 which started as a Bonny 650.
Last rebuild I did the big bore kit, 750 IN cam/late 650 EX cam, ported inlet, 32mm amal single and much more. Really, I cant feel a big difference for what it all costs to sort out in the tuning department. I'm very happy with how it goes but in hindsight, all the extra power I thought it would have beforehand was great expectations. Triumph got the 650 just right! Also, I must say, Mr Pete and I (helped), did a CC test on a big bore barrel and found 8.4:1 comp ratio which had a skimmed to the fin head with no head gasket. So with all the go fast shit a person buys he's only lookin at 7.5ish comp ratio with an unmachined head and gasket. And it aint a matter of machining the top of your new BB Jugs to gain suitable comp to suit all your goodies because you'll stuff up the push rod tube height as the machined head does, yes, there's different size white square rings but hey,,this is what TUNING is all about, it's endless once you start, just to get it a bit better than a stock factory tuned 650. Most times it's worse, I'm still lookin for more but it's a matter of machining around the BOTTOM of the barrels so the comp ratio suits the cams and their timing, the larger inlet ports, pipes etc etc.
The makers of BB barrels make the comp ratio lower for a reason.
Cheers mate
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Old 08-15-2014, 06:06 AM   #17
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With a shorter rod, piston speed will be slightly higher near the top of the stroke and slightly less toward BDC. Not much in it.
Yes,but the distance travelled by the piston in one rotation of the crank is the same ,short or long rod...
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Old 08-15-2014, 09:49 PM   #18
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Default Re: T120R Engine Build - Sanity Check

...I think like Daddy Boy; in my opinion tuning these engines is for people that loves tweak here and there and prefer to be a mechanic than a rider...or to really ride the motorcycle.
For pennies the only change that you need to change performance is to change the sprocket and use a mid range camshaft; you see lot more with this only change than filing, tweaking, modifying, etc; lot of money, many more wshop hours...and never really a long ride.
I never ever meet a guy with a tuned bike that have a reliable daily ride or a ride to take the open road...but they love to put their hands on...then ride the bike couple of blocks or for a race...then drive a car or a new bike.

Also, the T140 s have all the factory mods if you compare them with the early Bonnies.
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Old 08-16-2014, 03:07 PM   #19
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Thank you all for the constructive criticism. Your feedback is much appreciated and valued. There is a lot of information to soak in but I think I have a better idea of what I have in mind for the initial final parts selection/combination.
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Old 08-16-2014, 03:30 PM   #20
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Default Re: T120R Engine Build - Sanity Check

If there was one thing I knew I would run for certain, It was a magneto. I've researched quite a few. I wasn't a big fan of the Hunt primarily because of the aesthetics and have heard of more than one negative feedback from various shops/people. From all the people and shops I've spoken to, it was the Morris that received the best reviews. I also liked the manual advance/retard features. The only thing I didn't like about it was it's orientation on the bike. My first choice has always been the ARD but finding one in decent condition was like the holy grail.

After much searching, I came across a member on IG who I was following. He was running a new production Ard cover fitted with a modern Morris Mag on his race bike.After further research I found out they were being built and sold in Australia by a shop called LyteDrive Engineering. I was able to get an email and received a call from John Scerri who was very helpful in answering my questions on this product. To be honest, I was a little nervous sending a bunch of cash oversees but to my surprise my Magneto arrived at my door step in less than a week. This is the crown jewel on my motor and can't wait to SPARK IT UP! Here is a pic

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