Valve guide install?

[TownsendsFJR1300]

Not a Yamaha but a Stihl, commercial, BR600 back pack blower "4 mix".

Customers blower that locked up. It uses pre-mix BUT is a 4 stroke engine (premix lubes the entire engine).

Customers workers are using the machine, WOT (about 8K RPMs) and it STOPS.

It has over head valves, head IS part of the cylinder.

Engine turns 180 degree's, stops SOLIDLY. A peek with a borescope shows the exhaust valve SITTING, intact, atop the piston. No damage can be seen to the walls, piston etc.

Get to the valve cover and find the valve guide PUSHED OUT of the head, apparently by the valve. The valve retainer FAILED(about 1/3 separated but everything still under the valve cover. Fish the valve back up into the head. Do a leak down test both at TDC (valves closed) and at BDC (checking for potential damage at the lower end of the stroke).

Leak down is 98- 95% with the exhaust valve in (NO VALVE GUIDE) no matter how I rotate the valve back and forth. The valve stem appears to be straight (just looking and putting a straight edge to what I can access. ( to remove the valve, the engine / unit needs a complete tear down ((more expensive than the unit is worth)).

I already have the correct sized aluminum "collar" that slips over the valve stem and just enough covering the guide.


*Now the question, I'll be trying to install a new guide WITH the valve installed. (Piston at TDC with rope inside the combustion chamber holding valves closed-and crank locked up).

Is it best to freeze the guide and most importantly, tap in with a hammer (and some lube), OR very light impacts with the air hammer set super light so I don't destroy the guide?

Note. as the head is part of the cylinder, I'm sure guides were initially installed from the top..


Thoughts?

[walleye1]

Pack the guide in dry ice for a hour. Wear gloves.

[99yam40]

98% leak down is bad, or am I looking at that wrong.
head of valve is bent/not seating properly?

[TownsendsFJR1300]

98% leak down is bad, or am I looking at that wrong.
head of valve is bent/not seating properly?

Worded incorrectly on my part.

Leak down @100 PSI is 2-5% depending on how I rotate the valve. IE, it's 98-95% TIGHT, (darn new new!!). That's tested with the piston at TDC and at BDC (valves closed).


That valve is just about perpendicular to the piston and when it dropped, and came back up, it apparently popped the valve guide out W/O any other damage...

Just cleaned up the valve stem with some emery cloth, thru the exhaust port (PIA).


The broke spring retainer:





Close up under the valve cover:






Overall machine partially apart:

[rodbolt17]

me? if I am not doing it correctly anyway I would just pound in a new one and go have a cold one.
typically when we replace a guide or knurl one we use the guide to set up the pilot to cut the valve seat concentric to the guide.

[TownsendsFJR1300]

Thanks...

He's super cheap, the machines run hard (as you can see) and to cut the seat, the case splits at the crankshaft (so you have to reach down thru the cylinder to get to the "head").

Stihl is way worse than Yamaha, everythings buried beneath something else.

With the valve currently sticking out of the head, the valve is pretty much being used as a guide (it is seated).
With about 1.5' of rope inside the combustion chamber, it keeps the valve from dropping inside the combustion chamber...

[99yam40]

That could be a problem if the new guide is not holding the valve in the same exact center as the old one,
all you can do is try and see if the valve still seals off OKI.

I was thinking the valve seized onto the guide and pushed it out.
But sounds like you are saying the keeper came off and valve dropped down far enough( completely out of guide) to catch on the bottom edge of guide to push it. I did not think that would be possible for the valve to drop that far especially with it running any RPM

[TownsendsFJR1300]

That could be a problem if the new guide is not holding the valve in the same exact center as the old one,
all you can do is try and see if the valve still seals off OKI.

I was thinking the valve seized onto the guide and pushed it out.
But sounds like you are saying the keeper came off and valve dropped down far enough( completely out of guide) to catch on the bottom edge of guide to push it. I did not think that would be possible for the valve to drop that far especially with it running any RPM

Yep, that's exactly what happened... The valve pushed the guide out of the head. The guide was loose under the valve cover. The head of the valve, fit into the now, larger hole (stem had lots of room now) and locked up the piston from rotating (not enough clearance).

I did try re-installing the guide and did get it started (it did NOT drop in easily) and needed hammering, however, the valve was stuck in the guide (think the guide ID got damaged) and I had to pull it back out (with heat) and the guide cracked apart once vise grips got on it.

As posted earlier, I went thru the exhaust port (like a 4 stroke), saw a little of an "edge" and was able to sneak a thin strip of sandpaper(forgot the name, it's re-enforced), thru there and clean up the questionable edge. What's left of the old guide NOW slides over that area and doesn't hang up..

[panasonic]

Scott,

Correct me if I am wrong, you have a NEW guide to go in?

If so, once it is pressed into the head the ID may close up slightly and nip on the valve stem. Typically you have to ream the guide after it is installed to fit the valve stem.

I don't know if this would be the case on this engine but that has been what I seen doing other small engine heads.

Hopefully it will work out for you.

[TownsendsFJR1300]

Scott,

Correct me if I am wrong, you have a NEW guide to go in?

If so, once it is pressed into the head the ID may close up slightly and nip on the valve stem. Typically you have to ream the guide after it is installed to fit the valve stem.

I don't know if this would be the case on this engine but that has been what I seen doing other small engine heads.

Hopefully it will work out for you.

I don't have the guide yet. The block is aluminum, the guide steel. If it does need to be reamed, that would be an issue.

I don't have a ream, could obviously get one. I guess two ways to go.. drop the valve fully into the combustion chamber (but it'd be VERY DIFFICULT W/O a FULL tear down) to get it re-inserted..

If that was the case, it wouldn't be worth repairing, labor wise, etc.

**Do all / most new guides need to be reamed??

[TownsendsFJR1300]

Scott,

Correct me if I am wrong, you have a NEW guide to go in?

If so, once it is pressed into the head the ID may close up slightly and nip on the valve stem. Typically you have to ream the guide after it is installed to fit the valve stem.

I don't know if this would be the case on this engine but that has been what I seen doing other small engine heads.

I just looked at the inside of what's left of the old guide.

It's definitly NOT machined internally (NO hone marks, etc) and has the same darkish finish as the outside of the guide, so I think I'm good there (I hope).

It's a cheap investment in a guide and retainer vs the machine goes to the "parts pile" in any event...

[TownsendsFJR1300]

Update. Stihl does NOT sell the valve guides. It's part of the head/cylinder.


The Stihl mechanic has never changed one (the engine is considered trash at that point) and it took some time to convey what was needed.

My customer reached out and found 3 blown machines (at another dealership), and hopefully we can snag one for the part(s)…

The cylinder / piston / valve are usually trashed but the guides, away from all the action, should be fine...

[99yam40]

Good luck getting an old one out and back in the one you are working on without damaging it

[TownsendsFJR1300]

Good luck getting an old one out and back in the one you are working on without damaging it[/QUOTE]

Getting a guide out of a broke block, piece of cake.

As the block is junk anyway, drill / Dremel the aluminum around the guide and it'll about fall out...

I already have a small piece of aluminum that fits over the valve stem, nice and flat which will be used to hammer the "new" guide in.
The aluminum should prevent any damage to the steel guide and mushroom (if it's going to happen-shouldn't).

*When I did start to re-insert the old guide into the block, it wasn't difficult. The valve stem apparently had a nick on the end which jammed up with the guide.
Of course that wouldn't work and I had to remove it (that's when it got damaged with heat and a vise grip).

I've since cleaned up the end of the valve with emery cloth and what's left of the old guide, slips over the valve NOW, easily...

Just need a guide!

My customer (has a friend at a Stihl shop), found a PILE of engines dropped off at a shop to see about what's repairable. Obviously, many won't and I should be able to snag a block for cheap.. Heck, I can sell a good coil on Flea Bay and break even right there..

[TownsendsFJR1300]

Just an update.

Got a junk engine and cut the valve guide out of the head. Tapped it into the original head fairly easy but the valve kept hanging up once installed.

The valve stem was bent slightly so ended up doing a full tear down.

Installed the 2nd parts machine EXHAUST VALVE in the head. No more binding but leaks fluid (when held upside down) pretty bad...

Crank bearings had a lot of wear, lower seals leaking, some damage to the crank gear teeth (mesh's with composite cam gear)..

One bolt (engine to housing) seized bad but welding a nut to it popped it off real quick..



BTW, leak down test on the parts machine at 80 PSI showed about 20 PSI (no compression). I believe there's a small hole in the piston(kind of hard to see even with the bore scope)