M620 Worn Valve Guides

[Vishwacorp]

Hello all,

I have a rather significant issue with my 2005 Monster 620 Dark (30,500 miles) and I would appreciate your advice on what I should do. During its last service approx. 5000 miles ago, I was informed that all 4 of my valves are excessively worn and that is what was causing the stalling and lurching at lower RPMs. At the time, the valve clearances were adjusted to make the bike run better and I figured I'll get the guides replaced at a later time.

Now once again, my bike is stalling and lurching badly. The quote for all 4 valve guide replacement was around $1500, which I don't want to invest in the bike. So, should I -

1) Find a used engine and replace it? If so, what engines other than injected 620 and 695 engines would work?
2) Find used cylinder heads that would work with my bike and buy those? The advantage of this is that I wouldn't need to drop the engine out of the frame. Once again - what heads should fit?
3) Sell the bike for chump change and get something newer? Not sure how much it'll be worth but maybe someone else will be more eager to fix it than I am.

Thank you.

[thorn14]

1. 620,750,695,800 fi engines all fit drop in replacement with only ecu, maybe tps, and (unsure about 695) wiring harness. 900 and up require different headers. Expect to drop 1000 on a swap without even doing the valve adjustment/belts/oil. There have been swap so a search should yield results. (I went from a 620 to an 800.)

2. 620 heads fit and 750 heads fit I believe but I'm not sure whether you need the cylinder as well. Wait on someone smarter or do a search on the 750 upgrade. (I have 620 heads sitting in the garage if you decide to stay stock and cheap. Fully disassembled but with one valve guide that's loose.)

3. Likely not worth selling but someone may pay more than I would.

[Howie]

The issue, IMO, is what are you getting for your money.  A used engine will still use a bunch of the $1,500 plus install labor unless you do it yourself.  The engine need to do more than fit or computer modifications will be needed, not so bad if the ECU is compatible, but still more $.  And, after all that, you still have a used engine which may need repair down the road.  $1500 invested in your engine?  You know what you have.  Just food for thought.

[brad black]

a few points without prejudice, lest i be labelled grumpy.

is the person who told you the guides are worn familiar with how they would have felt when new?  it's a comparative thing, and they're surprisingly loose ex factory ime.

i wouldn't replace the guides unless they were loose in the heads.  i get them k-lined, which oddly enough for an american product appears to be hard to find in the usa.  any normal head shop should have them i'd have thought.

1500 is, imo, quite a lot to do a pair of easily removable heads.  get another quote.

given the base gaskets will have grey goop on them, i'd say you could just pull the heads carefully so you don't move the cylinders and refit without worrying about resealing the base gasket.  pop them off and get them done.

[Howie]

Yep, Brad has a really great point about a second opinion. I also should have asked more about your symptoms, like blue smoke on deceleration.  I didn't consider which shop gave you the bad news.  You will be getting an PM from me since I don't like talking anything but positive about shops on the internet.

[Vishwacorp]

I read through a lot of engine swap threads and it does seem like a lot of work if I change the engine size. Issues of all kinds from the ECU to fitment of various bits and pieces make it seem like a serious project. So I think I'll be dropping that idea.

Brad, the shop that gave me the news is probably the most trustworthy place around, so I really have no reason to doubt them. I'm going to speak to them about using k-lines vs putting in new guides. I had no idea such a product existed.

I did find a pair of 620 heads on eBay but they are with an "unknown" number of miles on them and of course, there's no guarantee that they don't have issues of their own so I'm a bit wary about going that route as well.

At the end of the day, the bike is already at 30k and I'm sure I'll enjoy getting it fixed and riding it past 50k. 

[Vishwacorp]

Update!

The shop ended up swapping the heads from a good 620 engine they had in their possession. The end result was a little cheaper than repairing the heads. The good news is the bike is running better than it has in a long time. The engine is more responsive than ever, idles perfectly, and seems to pull stronger past 6k, at least to my butt dyno.

Now the engine is ready for at least the next 31k miles. 

[koko64]

Glad that worked out.