When rebuilding a Nytro engine remember this!?

[kimoajaj]

Hi guys!

Dimebag and I will soon be starting to assemble his Nytro engine after a rodbearing went bad.
2008 engine with 12.000km on it, 10.000 of them with MCX 180 turbo kit installed.
In that matter I want to make sure that we don`t forget anything, I do work as an engine mechanic and have worked many types of engines but have never had a Nytro engine apart. I have worked at the local Yamaha dealer for a year and have done lots of valve jobs on bikes so I am familiar with the topend of these engines. Now I wrench on larger marine diesel engines.

I hope that this thread can help someone in the future and the reason for me posting this is that I want to make sure we are not forgetting something so all of you guru`s out there please tell us if we are overlooking something.

-All rod bolts has to be replaced (stretch bolts)
-All main head bolts has to be replaced (stretch bolts)
-8 bolts that holds the lower part of the block (the ones closest to the main bearings) are also stretch bolts and has to be replaced
-If a rod bearing has gone bad the best option would be to replace the rod (we are, another option is to have it checked for ovality)
-If minor scores or scratches have appeared on crankshaft journals - replace crank (we are)
-We are going to check both rod and main bearing clearances with plastigauge. Rembemer to use your old bolts when plastigauging since you dont want to stretch and reuse your new stretch bolts.
-Do not hone cylinders if you don`t know what you are doing, they are nicasil coated. I spoke to Erik Marklund and he said that he used some fine grit and gave it a few spins with his hand inside the cylinders just to give it a little more coarse surface to give it some of the benefits of honing.

We are also replacing all the valve springs (Dimebag wanted this), I will be lapping the valves carefully and I hope no re-shimming will be necessary. We are also replacing the oilpump, oilcooler and camchain tensioner. The reason for changing the oil-parts are that Dimebag felt this would be the best way to be 100% sure that no bearing particles could be left in the system. I agree, but I do believe that if you are on a tighter budget cleaning the oilpump should be possible, not sure about the oil cooler.

We are not replacing:
-Camchain
-Oilpump chain
-chain guides

I can`t see any wear that is worth mentioning on the guides. The chains feels really snug/tight with no loose or rattling links.
The same type of chains last from 50-100.000 on bikes so I cant see why it should be replaced.

I have read about some issues regarding setting up the camshaft timing on these engines, that the chain skips on the cams when turning the engine without the headcover installed. ? I hope it wount be giving us trouble when measuring the valve clearances.


Does anyone have some tips/tricks when it comes to putting this engine back together?
I do feel that we have things under control but I really want to make sure we are doing everything correct.


Joakim

 

[mike3577]

Ck valve guides for wear,replace valve seals and lube seals with grease,lube valve stems with never seize it stays there longer than you would think,re ring pistons and do a quick hone even on the nickle just enough to put in a fresh crosshatch for the rings to seat,lap valves like you said make sure the valves seat by putting a flashlight down the intake and exaust port in a dark room so you see if any light is getting past the valve face,u can also ck this by putting water in the ports to see if they are sealing 100%,if they arent water will leak past valve seat then new valves and cutting the seats would be required hope this helps lol

 

[Mtnviper]

Looks like you guys summed it up pretty good
About the only thing that I can think of off the top of my head is you may want to chuck the valves in a lathe or drill press. Then slowly rotate them and check for runout (bent) with a dial indicator.

Bill

 

[Dimebag]

re ring pistons

We will be replacing all pistons and rings.

 

[1975FA]

I check valve seal by flipping the head over and filling the combustion chamber with parts cleaning fluid, kerosene or diesil. It will run through a leaking valve quicker than water and can't cause rust. Just curious what kind of money is this job costing? More than a small block chevy?

 

[BADSLED]

Nice post!! Thanks for sharing your knowledge and experience. Can you elaborate, or give some useful tips on those removing and reinstalling heads for thicker head gaskets with higher boost turbos?

 

[Dimebag]

Just curious what kind of money is this job costing? More than a small block chevy?

That depends how much a small block chevy costs..
I believe were gonna end somewhere around 3000-3200 USD + taxes, and about 500 USD in shipping costs.

 

[kimoajaj]

Thanks for the replies!

I will be replacing the valve stem seals, I was also thinking about putting the valves in a lathe to check for runout and now that you guys mention it I will do it for sure. I don`t now the runout-limits but I hope this is written in the manual.
Removing the valve springs will be somewhat difficult cause the compressor-tool I have is made for car-heads but I had a machinist at work make me a more suitable collar-cap-tool (dunno the correct word) to push the springs down to remove the retainers. One thing that is very important is not do damage the areas around the springs that support the valves spring caps (that touches the camshaft) when you compress the springs.

My plan is to get the head done on Saturday and also change the bearing and seal on the PTO shaft, I will also be doing some cleaning so that the cases are ready to be assembled. On Monday Dimebag and I plan to start putting it back together.

When we are done I will tell you all about it!

When removing the head to install a thicker gasket you do it as per manual except the fact that the cam sprockets has to be removed and the screw holes in them has to be modified (larger/oval) to get the thiming correct.

Before I remove a timing chain wether its a belt or chain I use a good degreaser and clean an area on all sprockets/chain/crank and use a paintmarker to make some marks just to be 100% sure that the timing gets correct. It is basically not necessary but when in doubt wether the factory marks/notches are 100% lined up, the paintmarker marks can confirm that everything is correct. (as long as the crankshaft is in the correct position).

If you look at the distance between two teeths on the cam sprocket you can imagine how far off the timing marks would be if the chain is a tooth off so in my world I find it hard not getting it correct.

When loosening the camshaft caps it is important to loosen them evenly, same goes for putting them back. If you screw all screws down by hand you might get the caps all the way down on one side but not on the other because the camshaft is pushing on the valves, therefor it is important to screw them down evenly. As you tighten the screws the cams will often want to rotate cause the cams will gradually put more and more pressure on the springs and the cam wants to rotate to an area where the cam has less lift. To prevent this, zip tie the chain to the camshaft sprockets with some small zip ties, pay attention to the crankshaft timing marks wilst doing this. After having engaged the chain tensioner and having rotated the engine a couple of turns, check the timing marks. This works on motorcycle engines but I know the Nytro engine is known for being tricky to time up so I will get back to you on this.

Cheers

 

[jaydaniels]

I recently rebuilt a nytro motor and the chain skipping while adjusting timming was a real problem for me. In the end what I found is that the spring in the tensioner is not strong enough to keep chain from skipping. What I did was back the bolts out allowing the tensioner to move away from the motor which allowed it to go to the next notch. Then tightened the bolts and that tightened everything up. Once the motor is running the tensioner is hydraulic. Hard to explain but hopefully this made some sense.

 

[kimoajaj]

Hi there jaydaniels!

Thanks for sharing your experience.
One thing I wonder is if it is possible to overtighten the chain by using your method?
In another thread I read the the valvecover has a chain guide that prevents the chain from skipping. But when you check the valve clearance and have to turn the engine it shouldnt be necessary to install and remove the valve cover everytime you turn the crankshaft.
Did you check your valve clearance afterwards?

We now have everything we need in order to start assembling the engine. I replaced all the valve springs and stem seals. The valves and seats looked very nice so I only lapped them with the finest compound. There was absolutely NO leakage from any of the valves, I doubt that there was some before the valves were lapped but.. atleast we know that they are all sealing good.

I also replaced the bearing and oil seal on the PTO shaft so now everything is ready to assemble.

Hopefully we will have it upn running before the weekend

 

[Tarzan]

Keep up the good work and trow in some pictures as well

 

[jaydaniels]

I also had some concerns with the chain being too tight. I installed everything and turned engine over by hand using zip ties to keep the chain on. Once the tensioner was as tight as it was going to get I backed out the bolts very slowly listening for the tensioner to clink to next notch. Chain still was not extremely tight buy no longer skipped. As for the cover you are correct, there is a guide on the inside and I tried turning over with cover on and still had issues with the chain being too loose. I can't say with 100 percent certainty that what I did will always work but was the only thing that seemed to work for me. I just couldn't chance starting the motor with the chain slapping around hoping it would be okay.

 

[Beenba]

Lap your valves while your in there. Checking them for run out is mandatory IMO.

When rebuilding my boosted honda this summer I checked for valve run out but never lapped them to the head. Lets just say the head came right back off after about 100km.
The valves were straight but they didn't seal well against the valve seats..I have stiffer springs too. The valve seats were just worn a bit.
For the 20 minutes it took me to lap them, I should have just done it in the first place, plus it guarantees a nice fresh seal!

 

[kimoajaj]

I must say that the chain skipping issue sounds scary, it`s just like theres a 50/50 chance that you will ruin your rebuilt engine on the first startup.. how can this be??

Following the service manual normally always keeps you on the safe side but there`s clearly a first time for everything? If the chain skips when firing her up for the first time then I think it`s best to go for a walk down to the harbour and then take one step further when you have reach the edge of the harbour, then stay there.
Maybe I should give Erik Marklund a call and ask him, he has rebuilt many many Nytro engines.

As for the valves they were all lapped and checked for runout, all were OK. I really doubt that any of the valves were leaking before lapping cause both the valves and the valve seats looked pretty much new, atleast that is my opinion.

Sadly I have to work overtime at work all week so Dimebag and I wount be wrencing on the Nytro engine this week, it was a huge disappointment not being able to put it together before Dimebag goes on vacation so that it would be ready for his return but that is just the way it is.

Will keep you posted.

 

[ShootToThrill]

The valve clearance can be set before the head is installed. The cams can be held in place with a large clamp (I forget the name but it was from home depot with the plastic pads on the faces). Clamp it in place with the lobe tips up on the valves you are checking. Measure it up and select the right shims and then put it together. Then when we did the final assembly we only had to roll it over a couple times to double check it. That saved us from removing the cam caps many times to change shims and saved on how many times you roll it over to set it up . On final check all was perfect and didn't have to change a shim. We set up a brand new head, valves, shims etc this way. I would replace the oil pump chain also, it's not expensive at all.