Top end rebuild. stuck

[Lamin Sambou]

it was all going so well untill I put the head on

Have I got a different barrel????

they both say 34K00 Y1 and look like this


but it seems the holes for the 4 bolts that hold the head on are a different depth

on the old barrel, all 4 holes are about 43mm deep

on the replacement barrel, the two holes on cam chain side measure 30mm deep, other two measure 40mm.

all 4 bolts are the same length

whats going on? can anyone throw some light on this, thanks

[aukeboss]

I do seem to recall there has been a modification ... Recommend either to get the correct bolts (some digging in old parts manuals required) or to drill & tap the holes in the new cilinder.

rgds
Auke

[Lamin Sambou]

Originally Posted by aukeboss

I do seem to recall there has been a modification ... Recommend either to get the correct bolts (some digging in old parts manuals required) or to drill & tap the holes in the new cilinder.

rgds
Auke

Hi Auke, thanks for reply, I took the option of making my original bolts shorter. also the 2 long M6 bolts that go from the head cover right through to the barrrel had to be shortened a bit. looks like yamaha made the holes deeper on later 34K00 barrels?

I found this info on later barrels in the archive from a chap called Klaus

as far as i now there is no barrel with code 1VJ.
34K01 barrel was used in 1VJ 1986 together with cylinder head coded 1VJ. the head gasket has 5 bolt holes.
because of the well-known overheat troubles in 1VJ engines, yamaha came up with the 34K02 barrel in 1987 (which made troubles even worser than before), again with 1VJ head.
than, in late 1987, yamaha introduced the 34K03 (also with 1VJ head). this one was o.k. because of longer threads for head bolts.
the xt600 2KF model which came on market in 1987 was also equipped with 34Kxx / 1VJ.
then in 1988 both tenere 3AJ and 2KF where equipped with the advanced 3AJ00 barrel and the 2KF head. from that day on untill nowadays every xt600 is equipped with this barrel and head.
it must be stated that every barrel fits every bottom end, you only have to take care about the barrel / head combination. so, 2KF head will fit only on 3AJ00 barrel while 1VJ or 34L head both will fit on 34Kxx.
the difference between 1VJ and 34L head is the smaller valve diameter of the latter.
the difference between 1VJ and 2KF head is the 6 bolt fixing of the latter plus the bigger distance between the two downwards facing fixing M8 bolts (in cylinder head).

cheers

[XT GIRL]

Is it also likely that a previous owner could have made the modification?

I have three 1VJ engines - all 34k00 y1 barrels - two of them have 30mm holes on cam side and 40mm holes on other side. All bolts are 105mm

The other engine -- holes are all 5mm deeper - bolts longer.

PS::: Is that the STANDARD original piston???

[Lamin Sambou]

Originally Posted by XT GIRL

Is that the STANDARD original piston???

no its a new replacement oem spec .75 oversize





the old one


the worn bore and piston was letting loads of oil past

cheers

[XT GIRL]

Oh HA HA!

I recognise that old piston!! (from your other post!)

How has it all gone, by the way??

[Lamin Sambou]

Originally Posted by XT GIRL

Oh HA HA!

I recognise that old piston!! (from your other post!)

How has it all gone, by the way??

all back together and no smoke now

not sure what sort of running in is recomended on a rebore & new piston?

next on the list of things to do is

sort out carbs - i've got another pair to try out and fiddle with.

sort out excessive vibes (really bad over 50mph) - not sure where to start with this, can anyone can give me a list of things to check engine wise?

and when its all running right I'll look at cosmetic stuff

[bacardi23]

For the excessive vibes you have to go cosmetic! lol

Replace the XT's stock front fender with one of those from the YZ or WR!

makes a humongous difference on the vibes at higher speed!


Vando

[wolfzero]

when running in use cheaper oil don't use synthetic try and keep the revs down short shift when possible when you have done 250 to 300 miles change the oil and filter then ride pretty much as normal but try and avoid sustained high rpm's though until you have covered at least 500 to 650 miles since the rebuild do another oil and filter change if you want to.
i'd do an oil and filter change at 1000 miles if you don't do one at the 650 mile mark after that your done with running in these big singles don't need that much running in.

[bacardi23]

If you say to put cheap oil just because it is expensive as you need to change it on the first few couple hundred miles you make a good monetary point...

BUT in terms of engine reliability, USE THE SYNTHETIC OIL and try to always use the same oil as changes in different oils will lead to a decrease in reliability!

In the first few hundred miles do as wolfzero said, when changing the oil also change the oil filter!

Don't sit on the throttle in the same position for too much time and go easy on the engine, use all your gearbox up to a little over mid range. Do not rev the engine too high.

Try to avoid speedways..bad bad bad for the break in when done wrong!

When you get 175-200 miles on the clock do push the bike from once in a while with a minimum of 50-100 miles difference!
Make a stop, engage 1st and juice it all up till 5th without revving the gears too much.
When you're just a little below top speed start slowing down but not too harshly! (AND DON'T engage the clutch while on top speed and go down from 5th to 1st like I've seen some dumbarses doing!) Use gearbox braking and the brakes!!!!

I am tho a little more carefull as between oil changes especially during break in...
When I replaced the Piston, piston rings with some wider ones, camshaft and chamshaft bearings on my 2002 DT125R I changed the oil at 300 miles, 600miles, 1200miles, 3000miles and finally at 7000 miles and every other 4000 miles!
It now has almost 70000 KM on the clock from which 40000 have been done with the recent engine work.... And I'm everything but gentle with that bike!

Vando

[Lamin Sambou]

Originally Posted by wolfzero

when running in use cheaper oil don't use synthetic try and keep the revs down short shift when possible when you have done 250 to 300 miles change the oil and filter then ride pretty much as normal but try and avoid sustained high rpm's though until you have covered at least 500 to 650 miles since the rebuild do another oil and filter change if you want to.
i'd do an oil and filter change at 1000 miles if you don't do one at the 650 mile mark after that your done with running in these big singles don't need that much running in.

Thanks, I'll stock up on a few oil filters and I'll have to guess on the mileage as my speedo works but not the mileage... (stuck on 54,000 not sure how long its been like that)

I dont want to start an oil debate but I'm using the semi synthetic from Heine Gerrick as its cheap. some have said fully synthetic messes up the clutch, not sure on that one.

any idea's on the stuff to check on engine regarding the vibes?

nice supermoto by the way, I'm amazed at corner speed & turn in on my 25yr old XT with Scorpion & Distanzia, yours must be a lot of fun.

cheers

[wolfzero]

DO NOT USE SYNTHETIC OIL WHEN RUNNING IN ANY RE BUILT ENGINE YOU HAVE BEEN WARNED!!
the semi synthetic is fine these engines dont need to be run on fully synthetic anyway as the oil spec for these motors was written a very long time ago in oil spec terms.

thanks for the compliment it handles very well i got it so far over it ground out the foot pegs.

these engines are vibey but double check all nuts and bolts are tight especially things like crank balance shaft and flywheel/magneto.

[aukeboss]

A few things that could be checked:
- Carb settings -wrong settings make it run harshly. Start with standard factory and change from that depending on modifications in exhaust and air intake
- Check that all engine to frame connections are at the proper torque

Good luck A

[Lamin Sambou]

Originally Posted by wolfzero

it handles very well i got it so far over it ground out the foot pegs.

these engines are vibey but double check all nuts and bolts are tight especially things like crank balance shaft and flywheel/magneto.

thanks, where do I find the nuts to check on the balance shaft?

and top marks for getting the pegs down thats a long way over

[wolfzero]

the balance shaft nut i mentioned is the one where the timing gear to the crank fits on it should have a tab washer on it too its situated under the clutch cover.
i put some dunlop d207's on it and at first thought i'd not put the wheels back on properly as i heard a scraping noise then i went round a rounderbout with my foot on the peg and felt it lift the peg and squash my foot