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Discussion Starter · #1 ·
Good day all.. well just not for me.. just did compression test for my rd07a
First cyl.
Gauge Motor vehicle Measuring instrument Font Auto part

Second
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? Did you have the throttle grip twisted right open to let the air in ?..If it's really that low ? it should be pumping blue smoke out the back..
 

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Discussion Starter · #4 ·
Ok, did test again yesterday, just forgot to twist the throttle :)
Now looks a bit better
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Gauge Motor vehicle Measuring instrument Gas Font
 

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Discussion Starter · #6 ·
Yes, its fully charged battery, in good nick, but i do have oil consumption 250-300km I should add not less than 1liter
 

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Have you had the bike long..what oil is in it ? Is it due an oil change ? If it got a really thin grade oil in it will use more. Needs a proper bike oil of at least 10/40..could try a 15/50 if your in hot climate.
 

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Discussion Starter · #11 ·
Ok, I decided to do engine work. Will get first of all both heads to check, bottom will go after ill be sorted with heads.
After bottom end will be checked i will decide what to do. To get oem pistons or to go oversize project
 

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Discussion Starter · #12 ·
Have you had the bike long..what oil is in it ? Is it due an oil change ? If it got a really thin grade oil in it will use more. Needs a proper bike oil of at least 10/40..could try a 15/50 if your in hot climate.
Ok, i have bike for 2-3 years, year ago it was underwater. But i'm not quite sure oil consumption got worse from that day’s. I use 10w40, owner before me, used to use 20w50
 

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Oil consumption with reasonable cylinder compression in high millage (or Km) can also be the top rings moving up and down in the ring grooves, which tend to pump a small amount of oil up to the combustion chamber with each stroke. If you remove the barrel, squeeze the ring all the way into the groove with your fingers and see if the ring can still move up and down noticeably in the groove. If it does, you need new pistons as the ring has hammered the groove wider. This is why high revving engines have thinner rings to reduce the effect of inertia at the top and bottom of each stroke.
If you remove the head and look at the piston top, if there is a clean area on the thrust and opposite side, with carbon in between, then oil is being passed up into the cylinder by the rings fluttering in the grooves, which removes the carbon.
This cylinder can still give good compression if the rings to bore clearance is still good.
The cylinder that is showing only just over 105 psi is probably leaking past one or more of the valves (seats). Although it is not bad yet, it will only cause a slight power loss at lower RPM only, but if you have the head off, it is worth re cutting the valve seats and valve faces etc. Also check the valve to guide clearance. A certain amount of wiggle is acceptable, but too much will allow oil down the inlet guides under high vacuum, but not so the exhaust. To check this before dismantling, with the engine hot, go down a hill with the throttle closed for some distance. Then blip open up throttle and looking in your mirror, if you see a puff of blue smoke (not black! too much fuel!) then the inlet guides/ valves/ seal are worn. This is best observed by someone following you and filming if possible.
If you replace the pistons and go oversize, depending how big you go, weigh the original piston complete with rings circlips and importantly the piston pin and try to make the new on the same weight as accurately as possible.
This is to prevent upsetting the engine dynamic balance, which can cause problems.
As the new piston is likely to be heavier, equalizing the weight is best done by removing material from the piston pin, as steel is heavier than aluminium. Do this not by boring out the inner bore as this will weaken the pin, but tapering from each inner bore end so as to create a small cone appearance. This as long as it is done in moderation will not affect the pin strength and is often how the manufacturers do it.
Do NOT remove metal from the pin ends as this will allow too much pin end float which will be catastrophic!
Lastly, if fitting new piston/rings, run the engine in for 250/500 miles on mineral oil, NOT synthetic or part sythetic, as the qualities of synthetic oil will prevent the rings from ever sealing with the bore and it will always burn oil!
After running in fully, then use Synthetic oil !
Hope this helps.
PS, If you do change the pistons i would be interested in knowing the standard weight, as i may do a big bore engine
in the future.
 

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Discussion Starter · #14 ·
Hi. Weighting piston sets is a good idea, but I am still struggling with myself .. should I go with big pistons ... or OEM pistons ... or stop investing money in this bike ...
 

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It depends on a few things, how good is the condition of the rest of your bike, how much money you are you prepared to put into engine rebuild. How much knowledge you have to rebuild. My first engine rebuild I needed help which I got from a friend so hopefully someone can help you. Its good fun when it goes right. Africa twins in the uk seem to keep a good price so factor that in. Another factor is time how much have you got to rebuild. Is your bike running. Last option is to drop it off at a good bike garage and let them rebuild it.
 

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Discussion Starter · #16 ·
Its giod enought, last year spent a fortune on the bike
Tire Wheel Vehicle Automotive tire Motor vehicle

Full frame paint, all OEM bearings, even swingarm, full body paint, rear side panels kevlar composite, etc.

I just thinking, should I spend 1k eur on the top or just leave it in a corner. Nobody wants to pay me 4500 euros for the bike at the moment.

all work should only be done by me, no other workshop. I do not trust anybody..

or maybe there is simply a lack of inspiration at this time ..
 

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I remember reading your thread now and you have a very nice Africa twin. I would definitely repair because you will get very little with a engine burning oil. My opinion you don't have much choice. Fix it up and start another thread showing rebuild. Use Honda gaskets for cylinder block and head. Good luck on your decision.
 

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Going with the largest OEM pistons would be the easiest and probably the most practical solution. It would give a slightly higher compression ratio which would be a good thing if running on E10 fuel especially if you alter the ignition map as discussed elsewhere on this forum. The slight increase in capacity would also be no bad thing.
The only non OEM pistons i know of are made by Hordpower in America but these are Honda Hawk racing pistons which i was considering. However using these would be anything but straightforward as they have raised crowns, so things like valve to piston clearance would need to be checked and possibly adjusted. I have a history of building race engines so this work and other such pitfalls are second nature, but should not be undertaken by anyone without this experience or an expensive calamity is very likely!
I am not sure whether these pistons would be feasible to use as i would need detail information about piston pin diameter, compression height and overall weight in comparison with the XRV piston. I am not going to strip my engine now as it is running beautifully, but if you do decide to rebuild your engine, i would be interested in obtaining one of your old pistons complete, so i can do the various measurements and compare it to the Hordpower piston.
Of course if anyone else has an old piston preferably std size that they dont want or would lend me, i would like it to take the necessary dimensions etc.
 

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Ah, i hadn't seen those, but i was looking some time ago!. These are probably the pistons that Hordpower use as they are for a Honda Hornet (600cc?), so no guarantee that they are the same critical dimensions as a 750 XRV.
JE (USA) pistons are good quality forged items as they are for racing, but can be used in road applications. This company is not to be confused with JE pistons UK who also produce forged pistons but in much greater quantities ( min order in the region of 2000 sets!).
Motorsport is so huge in America that it is not difficult to get pistons custom made, as i have done from the likes of Arias, (min order 2 pistons!!) but other good makes are Wiseco etc.
From memory the Hordpower (JE) pistons would give a capacity increase to 780 cc (in an XRV application) which may not sound much, but any increase in capacity will give extra torque. I was interested mainly to increase the Compression Ratio to over 10:1 for more efficient combustion with E10 fuel, but as i stated before as these are designed for the Hornet 600, using them may not be a straightforward job. JE can supply the relative dimensions for their piston ( probably as specked by Hord) but would not necessarily know the AT 750 dimension to compare to. You would definitely have to alter the ignition profile to get the best out of them, but i think you already have that option.
The valve to piston clearance may be ok as the Hordpower engine would undoubtedly have race cams which would have the necessary clearance, but still cannot be taken for granted and would require a dummy build check.
Dammit you are getting me interested in doing this again !!
What mileage / KM has your engine done ?
 
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