Take a gamble, get valves re-cut/lapped or cheap ... *FIXED*

[mike-s]

See my newest post if you are even slightly curious about the fix.

This is mostly me thinking out loud and getting some second opinions in the process here. Basically my GSX250 has valve problems again. When i bought the bike the problem was the past owner had let the valves go unadjusted and promptly burnt the shit out of one of the exhaust valves & seat and from memory didn't do much in the way of kindness to the other exhaust valve seats, hence i got it for a song as they bought it with the intention of fixing up, but it sat in their shed for 3 years before they sold it to me.

I replaced the shot valve, lapped it (probably should have gotten it cut at an auto-mech's down the road in the first place) and it "looked" like it was getting a good seal despite this damaged exhaust seat. Fast forward 4kkm or so to now and i did a compression check yesterday and got a grand total of 90Psi left & right. Compression check shows that it is likely valves again as squirting a few ml of 30w oil in there did nothing to improve compression. Aside from some headaches with tuning, the rest of the engine is in pretty good nick (new camchain, cams and followers are in great condition with no marks whatsoever, piston/rings/barrel seem good too).

I have found a engine at a wreckers about 200km away that is in an "unknown" state as it was sitting in the past owners back yard (in the bike) for 5-6 years before he sold it to the wreckers to get rid of it. I have been told i can get the entire engine as-is for $150 as they genuinely do *not* know the state of it. It could be a gem of a head but with worn barrels, or could be perfectly ok all around. Now I know it's a bit of a gamble in buying this engine just for the head and I'm looking at some other wreckers to try and just find a head, but thus far none seem to be quite as cheap as this one. For example one of the wreckers i called was after over $250 for a head that was on a bike that got all of 60/65 psi . I'm going to call another one of the wreckers back to see if he has another head for around the same price.

If i can't get a half reasonable head a lot closer than this one, would it be worth just getting this donk for the bits i need and parting out / keeping the rest for spares/ the bin? I am asking as i suspect that the seats in the current engine are too far gone to be of any use, and despite only getting an engine reconditioner to only cut the seats, I imagine with the cost of labour and parts (likely new valves as well as the seats) i would be up for a small fortune pretty quickly.

So yeah, failing finding another alternative head for cheap, think it's worth the gamle?

[edit]Just for further info i have taken the head off the current engine and there doesn't appear to be any damage to the face of the valves this time around, unlike the last time, doesn't mean the seats arent totally ratshit though[/edit]

[mike-s]

Current status is i'm postponing taking the gamble until i take the springs off and take the head / valves down to L.W. Parry engineering which are two minutes down the road from here to see what they have got to say. Hopefully i can do this tomorrow.

[mike-s]

Took the valves out, exhaust ones were a piece of cake, but the intake ones had the spring cap catching quite nastily on the valve collets and nearly bent the valvespring compressor in the process, but i got them out. (p.s. the valve collets are tricky little bastards to remove , i read somewhere to put a rag over them when compressing to remove in case, as i nearly lost one as it shot right out when the spring cap came loose.)

After a good clean of the combustion chamber and everything else, it appears that the valve surfaces look alright, though i am 100% sure that getting it professionally re-cut will go a long way for reliability/longevity. Either tonight or tomorrow morning I am going to take the barrel off and check for disproportionate/oval wear at the bottom end (i.e. if there's a gap for blowby at the end of the stroke).

If there is none then I'm going to take the head to the reconditioner and see what they have got to say regarding cutting the valve seat to spec. I might just bring the barrel too while i'm at it to see if they've got any suggestions they can give me, even if i can't find any sideways wear.

So at this stage it looks i might not need the mystery engine, at least not yet.

[Sulli]

check for valve guide wear while you have it stripped down many years ago had work done by parrys and all good work they bored a 250 crank case to accept 350 heads and barrels if you want head rework if waggots are still at greenacre they were the best imho

[mike-s]

Hmm, will check for guide wear shortly, as to over-boring, don't give me ideas.

[Jonno]

Mate, buy the old motor, recon that head of that and change over.
Depending on budget that would be the way I would go.

Looks to me ya keeping that shitter so you might as well have all the spares you can get

[mike-s]

I was thinking that as well. I might just go for a wander up to Newcastle sometime soon and get it when convenient.

As to progress, today i took the head to the engine rebuild specialists in search of some advice. One of the guys there had a bit of a poke & prod at the head and took it out the back to test the quality of the seal provided by the valves on some special testing gizmo out the back.

He hooked them up and came back and told me that the exhaust valves were "ok" in that they were retaining approximately 80% of their seal, which is within acceptable limits. The intake valves on the other hand were only retaining 60% of the vacuum seal, which he said was a borderline pass to fail, meaning they are basically leaking like a mofo. The guy was pretty confident that that would be the cause of my headaches and that cutting the seats wasn't required and all i would need to do was to give the valves a good lapping with a cutting compound.

I told him basically what i've said here, the compresison test dry & wet and how the rings were done 4000km ago and everything else in the engine was quite healthy to the best of my knowledge. I queried him about the possibility that slop in the lower end of the bore from side-on wear would be a cause of loss of compression. He was pretty doubtful about this being a cause of loss of compression, even if there was a little bit of wear, but from memory it was as tight as a nun's proverbial at the bottom of the stroke when i was refitting everything 4000km ago. Given that there was less than a 3psi difference between wet and dry runs and my concerns regarding the bottom of the stroke have been averted, I am pretty confident that there's little to no problem with the rings/bore, thank God.

An hour later I was in the garage at home and had a blister on the side of my right index finger 1/8 an inch across and the "rough cut" with the corse cutting compound was done on the intakes and i was starting on the fine cut. I'll give it another fine cut tomorrow morning and then give the exhausts a rough & fine cut, but i won't need to be anywhere near quite as thorough as on the intakes if what the engine guru has to say is true.

Oh and I previously had a problem with idling etc, which was driving me freaking screwy, with the head off i i found a tear in the side of the carb boots that i am doubtful made it all the way through, but in the meantime i filled/sealed it with petrol/gasoline resistant silicone and am going to see if that makes any difference. I am also going to compare the idle & main jets as was suggested earlier.

If i'm lucky i might have this sonovabitch working by nightfall tomorrow.

The super awesome bit was the guy was happy to just give me a bit of advice as i made it clear i was only seeking guidance as to what my next step should be, which i thought was a fantastic bit of customer service (it also goes a long way to explain why the company had been operating for over 56 years in the one location! and quite successfully too i might add).

[JonW]

Quick tip for those starting out with head work for valve removal.
If the head is on the bench, get some rags or foam rubber and place under the valve head you are releasing from the spring/s. Make sure the valve head is cushioned otherwise bent valves will result.
Take a socket the same OD as the valve spring retainer and place some rag over the valve stem and tuck into the head. This will catch the colletts should they decide to fly. Put the socket onto the spring retainer cup and give the socket a solid tap with a hammer. It might require several taps but the colletts will be released with no stress. Pick all the bits off the head and stack on some clean rag. I use a handy take away food tray, nicely large enough for 16 valves.

Using this method I can strip my GPZ900r head in about 20 minutes.

Actually used a spring compressor the first time around. took me a day to get the head apart.

[mike-s]

Or you could just buy/beg/borrow a valve spring removal tool like i went and did (bought) the only problem is it's for bigger mtors so i had to rejig it to work with the smaller motor by jbwelding in a socket to sort things out.

and yes the rag is something i should have done

[mike-s]

Well that was fun, spend a little while watching the world go by, lapping the valves in the appropriate manner (handy hint, a 7+cm length of neoprene tubing over the stem of the valve makes for a lot easier task than those daft suction cups on a stick or using fingertips on the valve stems themselves).
Was satisfied with the task and the outcome, the sealing ability of the head is looking a lot better. stuffed about putting the collets on, they can be a right bastard to put on if you don't find an easy way to do it (wasted a good hour just there).

Then started doing the heads up in the right zig-zaggy manner. EVerything was going well, then i recognised the feeling of a head stud starting to give way, then *SNAP* it sheered through. This is the second time this happened to me with ths engine, the first was about 4 years ago.

*sigh* time to go order 8 more head studs and replace the bastards whenever they come in.

On the bright side i took the barrel off and had a look at the rings, plenty of meat left there, will measure the barrel wear when i can handle looking at this monstrosity again.

[Jonno]

Good thing is you learnt something and so did I, whats even better you did it yourself

[mike-s]

Had a look at measuring the bores and the lateral (side to side) wear is about 0.1mm compared to the top of the bore and the fore/aft wear is 0.2 on average (unfortunately my digital verniers only goes in 0.1 increments, not 0.01mm, I might get one that does to be precise), so at the very least wear is over the wear limit of 0.1mm according to the manual even using my relatively inaccurate tools. From what i can tell by measuring in-place, the piston is u/s as well, being 0.1mm undersize at the bottom of the skirt due to wear

Fortunately i've found a set of barrels, rings and matched pistons with 8000miles on them for a pretty cheap price, will go about arranging for them i guess. Go figure, it's turning out it will be cheaper to buy these from the US than just buy the barrel from a wreckers down the road.

[Sulli]

mike I usually use a cordless drill to lap the valves set to low speed beats blisters any time

[mike-s]

I tried to do that, work smarter not harder, etc. Unfortunately the drill wasn't able to reach in due to the small space in the 250's head.

[Jonno]

Had a look at measuring the bores and the lateral (side to side) wear is about 0.1mm compared to the top of the bore and the fore/aft wear is 0.2 on average (unfortunately my digital verniers only goes in 0.1 increments, not 0.01mm, I might get one that does to be precise), so at the very least wear is over the wear limit of 0.1mm according to the manual even using my relatively inaccurate tools. From what i can tell by measuring in-place, the piston is u/s as well, being 0.1mm undersize at the bottom of the skirt due to wear
.

You need an internal micrometer.

(and no it isnt a reference to anything but measuring tools as I am sure there are plenty of external or outdoors mikes here)