Xj 750RH Compression, valve clearance, timing.

Hello guys, after screwing up big time installing new boots(thanks to @Roast644 for sending some to me ) and forgetting a piece of towel into my #3 intake, engine would not start, made the stupid move to keep trying, removing airbox and spraying starter fluid, even that would not start the engine (and I cranked it a lot...)

Next morning gave another try and engine started, very rough untill I heard 2 loud bang bang before stopping it.

Decided to do a compression test so I rented one from oreilly... after noticing a 5psi on cylinder #3 I took the carbs off, inserted boroscope and realised my misstake...

Anyway. Managed to remove what I could see with pliers, and sending some air into the spark plug hole with the valve halfway of the seat.

Next morning unplugged tci, jumped a fully charged car battery onto the bike, and started a full compression test.
Engine mileage :41886 (my dumb brain didn't noticed before, trusted seller saying it was 4100)

From left to right sitting on bike :
92;110;87;110
After adding 1teaspoon of oil:
135;155;145;165

Decided to check valve clearance
Noticed timing not looking right...


Noticed damage on cam lobes


Took valve clearance 90degree from shim bucket

Intake :
0.10mm, 0.04 ; 0.25mm, 0.10 ; 0.08mm, 0.03 ; 0.15mm, 0.06.

Exhaust :
0.05mm, 0.02 ; 0.20mm 0.08 (tight) ; 0.13mm, 0.05 ; 0.18mm, 0.07.


I haven't taken the shims out yet, I'm wondering what I should do... seing the compression, damage on the lobes and the timing being wrong...

Should I take the cams off and get the timing right? Recheck clearance and check/adjust shims?

Or does the head needs to come off?

It's my first bike and I really want to ride it, I won't give up on it no.matter how long it takes but I'm not very experienced and I need some advice and directions!

Thanks a lot!

 

Also does anyone know if it's possible to remove the head and piston housing without getting the whole engine out of the bike?

 

That's some bad luck about the towel, but I'm not sure anything is damaged. It does appear to have jumped time.

Your cam lobes look normal. They didn't machine the castings any more than necessary, so I think you are just seeing some rough machining on the sides there. I don't see damage on the cam surface. The bearing caps in the center that are not the thrust bearings are normal. These are just a spot for the valve cover to bolt to. There is not bearing journal on the camshaft here. Unless I'm missing something, I don't see any issues other than the timing is out.

Fix the timing, shim the valves and do your compression test again just as a double check. If you had bent valves you would see worse numbers on #3. And your lowest compression on #1 is the one with the tightest valves. I think you are still in good shape here.

 

Ok great insight! Thank you, good to know there is no damage. I have the haynes manual and been watching a few videos about taking the heads off and back on, but didn't see about just changing timing.
Could you tell me the process for just the timing?
I mean the order of the process, i will figure out the how to

 

Or could anyone confirmz it's my first time doing anything like this, even tho I read and watched probably every video about taking the heads off on YouTube.

If I just want to set the timing properly without removing the head, would the correct order be:
Remove head cover -> slaken belt tensioner Allen bolts (or remove?) -> set crankshaft on TDC -> move back a bit to expose camshaft belt sprocket hidden bolts and remove them -> back to TDC and remove the other ones -> remove cam caps in diagonal sequence.

Then once cams are free of the chains should I just move them to correct timing?

 

Sounds like you understand the process, other than you don't need to remove the camshaft or bearing caps. Yes, remove the cam chain tensioner. You also should have enough slack by removing just one sprocket. Then jump a tooth on the other sprocket to align that cam. Then align the remaining cam and reinstall sprocket.

As you are reinstalling the sprocket, keep the chain tight on the front of the motor. After completion, with the tensioner installed, rotate crankshaft by hand a few times counter-clockwise and recheck all timing marks.

 

Just noticed the sprockets are completely in wrong order... from left to right sitting on bike

Intake : I4 -> E4
Exhaust I2 (looks like it's been manually engraved) -> E1.

Should I leave it like that or put them back the way it should?

 

Wow, that's interesting. A couple thoughts here...yes, they should be returned to their correct spots. But who knows how long they have run in their current location and did they "self clearance" to their new location? And why did they even get pulled in the past?

You could pull the cams, put the bearing caps back on by themselves, and feel the inside bearing surface with your fingers at the split. Is the transition smooth, or offset at all? Since you are already this deep into it, might as well.

The other thought is, just leave it alone and run it with the caps in the wrong spot. Whatever will happen has already happened. Might get another 50k miles out of it. Might blow up in a month. There isn't a procedure in the factory manual that covers something like this. Cam bearings are lightly loaded compared to the crank. The bearings are just aluminum. I suspect they will run in pretty awful conditions compared to many other wear points in the motor.

Silver lining, however....education is never free. Just think of how much you will know by the time you get done with this!

 

That's true, I'm learning so much everyday!
I have the plan to really work on this bike, properly paint it, and do some upgrades when I can afford it.
So I'd rather fix it properly and learn than be like YOLO and risk to destroy the engine on the highway, hurt myself or else.

I'm taking the cams off, got everything lose right now, I will check the bearing caps texture.

I noticed the crank moved a little bit off the TDC, is it safe to move the crankshaft once the cams are off and put it back on TDC?

 

When the cams are removed, all valves are closed so you can move the crank wherever you want. Just keep your timing chain pulled up so it doesn't wad up underneath the crankshaft sprocket.

 

Noted, thanks

 

Have you watched @Mezzmo channel on the engine rebuild. It's a 650 with bigger pistons barrels etc well worth a watch.

 

I've watch every single video on the xj650!
I wish I had his skills!!

I don't know if I would be able to dismantle everything like that without f***ing up tbh, but I might take the top end off and do the valves, im thinking about it, never done it, but I want to learn. That would mean I need to buy a head gasket, or a full gasket set will make more sense moneywise

 

I'm stuck, I removed the tensioner before doign anything but there is too much tension on the belts to remove the cams, I don't want to force it because if it rotate I might bend a valve.. any idea?

 

It looks like you have removed the bolts from the sprockets, but you haven't pushed the sprocket sideways off the shoulder on the cam. You have to do this to get the clearance, then you can flop the chain off the sprockets completely.

 

Snap, was I supposed to remove those one too? There's a few videos I watch and people didn't remove them, or at least I don't see it...

Is that my issue?

 

Yes, 2 bolts per sprocket. Remove them both.

 

Ok, I think I have to put everything back togather to remove those first, I f***ed up...

 

If you remove the plugs and use a pencil in each spark plug hole you can check if all four pistons are away from the valves. Or use a torch to see into each cylinder. Don't worry take your time be methodical. We all have been there.

 

Oh well, I was taking my time to remove the bolts, sweating my ass of in this Texas weather, and my freaking small 10mm wrench fell into the gap in the middle of the chain... I'm cursed.

 

I guess I'm attempting the top and bottom end now...

 

Well I think I just broke the crankshaft too. I feel like killing myself now. Wtf am I gonna do

 

Easily done, better than than one of the small bolts holding the sprocket to the camshaft. Do you have a magnet a telescopic one like the ones mechanics use?

 

King Kong could not break a crankshaft. You have not broken it.

 

I have one that goes straight, not spring loaded. Gonna try to put my $20 boroscope real quick. I just removed the cams. Tbh it might be a sign that I need to redo the head, already having all those misplaced caps on the top end doesn't make me really confident about the rest of the engine

 

Can't see it, it's a small one, size of a finger. I heard it fall all the way at the bottom of the engine

Gonna empty oil and take the head off

 

You can get the wrench out with a magnet. It might take a while, but it's a lot less work than tearing down the motor. If you get in too deep, you might find yourself overwhelmed.

It's an old bike. Don't worry about it being perfect. You're going to make other mistakes along the way. Don't sweat it.

Fish that wrench out, check your bearings (in the photos the cam bearings look pretty good), get it slapped back together.

 

Ok, it's about to be dark soon, I have a screwdriver holding the chain right now.

I'm gonna cover a clean plastic bag on the head, secure with rope, and think about what I'll do tomorrow. I think I should check out the valves, maybe change the gasket. I'm already at the point where the hardest is done to remove the top end so why not learn how to do it or even just check for leaky valves. I don't wanna have put it back togather and then realise I have a bad gasket or leaking valves...


But yeah about the lower end you're absolutly right, I'm definitely gonna get overwhelmed so I'll just fish for the wrench tomorrow

 

One question, I noticed when I removed every caps, that all of them had 2 screw with sleeves, with the bigger caps having 2 sleeves for 4 screws. All of them exept the 2 caps on the right side of the engine closest to the cam (only 2 screws).

Is it supposed to be like that or are they missing?

 

What you are describing is correct. Nothing is missing.

 

If you remove the head you must fit a new gasket.

 

Yep, I'm aware, but seing my compression test difference dry vs wet, I might have either valves leaking, piston ring, or head gasket. I have to work on other parts of the bike, paint and polish, fix break master cylinder, break line. Some parts I bought a long time ago but didn't get into it.

So I'm gonna check out valves try to fish for my wrench, and save up to buy a full gasket set!

 

Yes better checking everything.

 

Yep, I just hope no bent valves, especially exhausts, I was able to see some intake valve for sale new for about $10 each, but no exhaust valves :x will know soon

 

I'm stuck, I removed everything, exhaust, all front and rear nuts, and head bolts, in sequence, half turn each... some of the bolts were loose, and the last person who worked on the engine probably never heard of a torque wrench.

Anyway got everything off exept the cam chain front guide, at first i forgot and started using rubber mallet on the sides of the head, but nothing moved so after checking again I noticed it. Tried to remove by pressing on it and pulling it up, but it's not really working.

Is it necessary for it to be removed before taking the head off? I don't see any instructions about it in the haynes manual

 

Chain guides don't hold the head on. Did you remove the nuts from the 6 studs on the bottom? (4) M6 and (2) M8.

 

Got it off!

Not sure of how it looks it's the first time I'm doing this.

Seems like there is a lot of oil around one of the valve (where gasket material is) maybe it was leaking?

I'm gonna look up and do a leak test with gas and air, I saw that in a video

 

3/4 intake leaking, one is really bad.
Exhaust valves seems to be fine

 

There is a bolt and locknut below the cam chain tensioner housing opening in the barrels. Slacken the locknut and back off the bolt, that will allow you to remove the inlet cam guide if you want. You don't need to if you are not dismantling the engine further.

 

Do I need to do that to remove the piston housing? I'm not going further than piston housing and pistons, I just wanna clean up, check the rings and walls, I can feel some scratches on the piston walls I removed the front nut and washer but housing isn't budging.

I've sealed everything with plastic bags and tape, I'll probably try to remove it tomorrow, I'll have my wife vacum the gunk when I lift it off. Still have to get my wrench, been fishing but it's not biting!

 

If you want to examine the pistons and rings you will need to remove the piston housing meaning cylinder juggs or barrels. There is a nut holding the barrels to the crankcase at the front of the engine in the centre between cylinders 2 & 3. Yamaha also put tubing around the cylinder studs at the front of the engine to protect them from road dirt. They can be seen through the fins. That can bunch up and make it more difficult to get the barrels off, also you don't want that dirt falling into your crankcases.

 

Yes, ive already took that nut off, ive read on the manual about the issue of that dirt, since my engine is still on the bike, I'm gonna have my wife vacuuming while I'm lifting the housing, hoping dirt can be vacum before falling in the crankase!

What is the process if there is severe scratching on piston sleeves? Can it be high grit sanded?

Noticed a few scratches, nothing crazy but I can't see much of the sleeves right now, I can inspect it more tomorrow

 

I would not sand the pistons they are aluminum. Wait and see what they are like first. Post some pictures for everyone to see.

 

Don't use abrasives on the pistons or bores.

 

Ok I got the housing and piston out. Some of the stud hose are cracked and broken, not sure what to do with those.

Here are the pictures. 2 of the piston sleeves have almost no wear feel, 2 of them do, one of them feeling very worn(last pic)

 

I think I need a new cylinder block, there is too much damage on cylinder 1 and 2. I'm not sure about pistons. I found cheap blocks in much better condition on ebay, I think I'll mix and match the cylinders with the best sleeves I will have when I buy a new block.

As for piston, since I can clearly see someone was in the engine and didn't put it back togather properly, is there a way to tell what piston goes where? I've labeled them the way they came out, but I'm not sure it was the original order.

I see on the inside on the piston there are different markings, two of them have T3 one T1 one T4.

Is anyone aware of the meaning of those marks?

 

If you buy a replacement block buy pistons with it. Don't know if @chacal or @hogfiddles have any.

 

Are each piston different from factory? I seen in @Mezzmo videos the new oversized one he bought were also numbered.

 

No, new pistons are all interchangeable between bores. Used pistons should go back in the bore they came out of (ideally), since the piston/rings/cylinders have "worn into" each other. However, it's not an end-of-the-world issue if used pistons gets swapped between bores, just make sure all the measurements (clearances, etc.) are within spec if swapping is done.

Most likely those are mold cavity indicators, pistons are poured in multi-cavity molds, and each cavity has a specific indicator so that if problems arise, it's easy to isolate which cavity is having an issue.

 

So knowledgeable, thank you!