Take a gamble, get valves re-cut/lapped or cheap new head?

[mike-s]

This is mostly me thinking out loud and getting some second opinions in the process here. Basically my GSX250E (the twin, cyl,not the 4 cyl/across) 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 **** 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 gamble?

[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 aren't totally r/s though[/edit]

[Agemax]

stick with what you know, refurbish your head properly then you know its all good, dont risk a second hand head and find out that is knackered as well

[mike-s]

That's what the general consensus is, I'm going to take the springs off the valves and take the remainder i have to the auto engine shop down the road to get a rough idea on a "worst case" scenario with regards to what needs to be done to get her ship shape again.

The "break even" point on the cost of that "unknown" motor is about $180, however i am leaning towards the "stick with what you know" which is what you mentioned, which is something i usually do unless I don't have a lot of other options.

However if even a basic rebuild price is starting to get a little silly i'll potentially be doing a bit of a drive to get this mystery motor.

You never know, i might be ridiculously lucky and there is enough original material left that i can get by with just getting the valves seats cut & lapped in.

[BentRod]

stick with your old head, as machining costs generaly are not too high. I have my valve seats ground for 5$ a seat, and got the valves lapped for free (frequent customer) just be sure to get ne vlave guides as well, and before you install, set the head upside down on some paper towel and pour paint thinner into the now upside down head. check the paper towel to see if any fluid is leaking past the valves. while you are in there you can put in some new rings too i suppose.

[mike-s]

Well the rings were only replaced 4 thou km ago when i first stripped the engine down to be honest, and the compression test indicates that they are holding up ok (i.e. wet vs dry test the reading is relatively still the same.

However i am considering taking the barrels off now and measuring the base of them to measure for wear that has made the barrels out-of-round, which i didn't measure with a digital guage the last time, and should have.

As to the valve guides (part # 11115-11470) they don't seem to be made any longer and i may have a bit of fun trying to track them down.
[edit]Correction, the importer has 4 in stock, but at $25 each i am going to go make sure that my current ones are ok before jumping on ordering them[/edit]

I'm getting the wreckers to do a compression check on that mystery motor as well just in case it gives a good wet compression test (if it gives a good dry one as well, that's just a bonus) in case i need to go down that avenue.

[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.

[Graham]

Valve guides maybe?

http://www.cmsnl.com/suzuki-gsx250-1982-ez_model13609/partslist/FIG3.html

[mike-s]

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 as to my past thread regarding idle issues, i found a tear in the side of the carb boot 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).

[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.

[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.

[mike-s]

Studs are out of the engine and pistons are off, now just awaiting parts being sent from overseas (Watertown & Northern Plains/USA as well as Israel) . Also got to pull the finger out and pick up new studs from the local bike shop, will do it on Wednesday.

[mike-s]

Parts have all arrived, new barrel is nice and shiny . New parts were cleaned right up and new pistons/barrel have been fitted. Head studs have been replaced and the nuts on the top will be left to another day.

Unfortunately i'm a goose and bought 0.5mm oversized piston rings for the gsx250, so i'll be doing an ebay sale for them very shortly. On the bright side the rings that were in there were already in great condition, so not that much of a problem (i hope).

[mike-s]

New parts are here and fitted, New studs were $10AU EACH, not so good. But that was made up for the bargain basement price of the barrel and pistons, which are in perfectly in spec. For the oil/no oil during refit debate, yes i used about 15ml of oil (0.5 oz) of oil per cylinder squirted down each barrel to help with fitting the pistons in. I'll be getting her running in very short order

Unfortunately i goofed and bought 0.5mm oversized rings, so re-used the current ones as they are in excellent nick. Will have to ping ebay as a seller methinks.

[mike-s]

Stripped the carbs down again "while i had them out" and gave them a check & compared the jets on the new vs the old. the "old" ones are 116's, the new are 117.5's, unfortunately the idle jets were damnwell impossible to read the markings on with the light i had last night. The difference is the "new" carbs come from a later era bike where it has exactly the same engine, but the exhaust is a must more free-flowing 2-1 compared to the 2-collector-2 that was originally on mine. As i now have a '83~ish 2-1 on my bike i'm willing to give these carbs a good go before feeling i need to resort to the original jets.

[mike-s]

Everything has been put back together, a compression test run successfully with 140psi per cylinder , even with a rather flat battery. Next up i need to check the carb vacuum test screws on the sides of the cylinders "in case" and for the hell of it.

I'm also going to buy a new set of carb boots and boot o-rings as they as well as the test screws are the only things left to finalise the equation, as i can't think of anything else that could be the suspect

But at least the compression headache has been solved and im back to the original problem.