What to do with a detonated top end

FreeRide · 01-04-2015, 03:04 AM

Hi Folks,
Really enjoying the forum. Ive torn my friends 02 gz250 (19k miles) down to find the source of a horrible sound, and after finding most everything fine, i pulled the head.

An exhaust valve seat chipped off, so the piston has some dents in it, and the bottom of the head as well. These all seem repairable, as does the bore, but my question is what to do with the head.

Can new valve seats be found and installed? On ronayers i can get whats called the valve spring seat (12933-38200), is this the broken part that is seen in the photo, to the right of the upper valve? It almost seems like this is a cylinder pressed into the head. If i can find the parts, i think i can do the work, or find somebody id like to give money to regrind the seats and valves, if thats something doable on these puny things. The valves look fine (surprisingly) but perhaps i should replace them altogether?

Or do i just buy one of these gz250 top ends on ebay for $360?

Anybody have good leads on finding these parts? Id like to keep the head running, seeing as everything but one seat seems fine, but i just havnt had any luck finding parts? Thanks guys!

Jordan_Ciaramitaro · 01-16-2015, 12:34 AM

Unfortunately, the valve spring seat and valve seat are not the same. Any good machine shop should be able to source and install new valve seats for you. Looks like there is quite a bit of damage. Do you know what caused this? Maybe valves severely out of adjustment? Not sure if these are adjustable.

FreeRide · 01-21-2015, 05:50 PM

Hi jordan,
I took the head to a shop and he said though its easy to bore out the valve seat and install a new one, it is unlikely to be cost effective. He expects to have to remove both exhaust valves seats, as the non-chipped one has had the aluminum of the head swedged up tight against it, so he's worried about it being cracked. Then theres the question if the valves are still sound, given the beating they got. All in all, his cost to fix it up and still leave be worried if i left a ticking time bomb in there was damn close to the $360 cost of a brand new head. So... thats in the mail currently. Surprisingly, the cylinder was still totally fine.

Replacing the piston, rings, and the head. So.. now ive got a spare cam cover, cam and rocker arms, perfectly fine. Anybody need em?

FreeRide · 01-21-2015, 05:54 PM

Oh, and the cause...

PO said he was riding along at 50 and heard a death rattle. Bike would crank and make a horrible noise. Then at some point the starter would click, and nothing moved. When i tore into it the piston was at TDC with a chunk of valve seat pinned between the piston and head, preventing full rotation.

The guy at the head shop assumes unadjusted exhaust valves overheating, which i believe. There was a bit of an exhaust leak between the cylinder head and head, which makes me think the thing was running with wicked tight/overheating exhaust valves for a bit before detonation.

Jordan_Ciaramitaro · 01-26-2015, 02:25 PM

Ouch, have you checked to make sure the rod isn't bent? Is the piston damaged?

I would clean that piston really good and look for hairline cracks.

FreeRide · 02-04-2015, 10:41 PM

SOOOO CLOSE.. But stuck now.Help?

I bought a new psiton, as the old one had been crunched by that chunk of valve seat enough that the rings were stuck. Crankshaft measures within spec though, luckily.

So, im at the step of installing the piston on the crankshaft in the cylinder...

I can get the new piston and rings into the cylinder on the bench jsut fine with a can-type ring compressor. Slides in easy, moves around nice, great.

But, then i want to push the piston out the bottom of the cylinder enough to get the wrist pin installed to the crankarm, but this is far enough down to have the lowest ring pop off. The manual gives no advice how to do the assembly of the piston into the cylinder. Id install the piston onto the crank, then drop the cylinder down onto the piston using a ring compressor, but the taper at the bottom of the cylinder liner makes the band type compressors useless. Is this taper meant to guide the rings in as you tap the cylinder down from the top? Seems like a great way to trash some rings.

What is the order of operations on installing a piston onto the crank, and getting it into the cylinder? Cant find any info anywhere. If only the damned ring was a sixteenth higher up the piston, you could insert the piston into the cylinder, then simple slide the wrist pin in, jsut like in this video.

FreeRide · 02-05-2015, 03:49 AM

Progress.

Engine back together.

Work flow for getting the piston installed, since i cant find it anywhere on the site.

I took the starter out to do this, easy, 2 bolts. Rotated the crankshaft from the generator bolt until it was just below TDC with the crank on the rear side of the bike. Then put the starter back in. Now the starter is resisting the engine backdriving, so you can put a bit of downard force of the crank arm and it wont jut plunge down into the crankcase.

Now, install the rings in the piston, as per manual, and attach piston to crank with wristpin and spring clips. New Gasket on, drop the cylinder jug over the cylinder studs until it rest on top of the piston, which should be well oiled, as well as the cylinder. Now, one by one, squeeze the rings as tight as possible by hand while jiggling the cylinder down onto the piston. This is positioning the crank arm jsut on the rear-tire side of TDC helps, lets you push down on the piston a bit. Didnt take much, as the tapered bottom of the cylinder sleeve does a good job of easing the rings in.

Worked quite well. Then just rotated the crank a bit to make sure the piston moves smooth.

Water Warrior 2 · 02-06-2015, 06:10 PM

A big+ for figuring out the puzzle.

FreeRide · 02-07-2015, 03:15 AM

It lives...

Twitchy Neutral switch. Doesnt like to start with the kickstand down as it doesnt think its fimly in neutral. Gotta figure that out. Cleaned and checked the the little switch guy behind the engine countershaft sprocket, and its first harness connection under the seat. No issues, but its definitely a vibration effected problem. For now, ill keep the sidestand up, (the bike feels like a low-slung feather compared to my KLR anyway). Maybe ill just bypass the switch. Safety third, right?

Also, those little individual motorcycle sized tappet feeler gauges are fantastic.

And of course, after 5 weeks of no rain during what is supposed to be the rainy season here in CA, the afternoon i get her running.... rain. Wont complain wont complain wont complain

FreeRide · 02-07-2015, 03:24 AM

So... for the folks in the future who are considering what to do with a detonated top end...
This may be premature, but the process seems to have worked. Total cost, not worrying too much about staying cheap, somewhere near 550-600. Had the cylinder honed, didnt really need it, but i wanted an excuse to learn from the guy at the shop. Brand spankin new head which came with a cam and rockers and cap i didnt need, new piston and rings. Also, bought all new gaskets, and had to buy some tools.

Overall cost effective? Meh... dunno. But i got the bike for free with its exploded engine, and i got to take a top end down to the crankcase for the first time, which was really neat. So as an educational investment, very much worth it. And now ive got a cheap commuter bike so i can take my beat up KLR off line for some decades deferred maintenance.

Ill let you guys know if there are any developments. Thank you for all your info.

01-21-2015, 05:50 PM	#3
FreeRide Junior Member Join Date: Jan 2015 Posts: 8	Hi jordan, I took the head to a shop and he said though its easy to bore out the valve seat and install a new one, it is unlikely to be cost effective. He expects to have to remove both exhaust valves seats, as the non-chipped one has had the aluminum of the head swedged up tight against it, so he's worried about it being cracked. Then theres the question if the valves are still sound, given the beating they got. All in all, his cost to fix it up and still leave be worried if i left a ticking time bomb in there was damn close to the $360 cost of a brand new head. So... thats in the mail currently. Surprisingly, the cylinder was still totally fine. Replacing the piston, rings, and the head. So.. now ive got a spare cam cover, cam and rocker arms, perfectly fine. Anybody need em? Login or Register to Remove Ads
	0

01-21-2015, 05:54 PM	#4
FreeRide Junior Member Join Date: Jan 2015 Posts: 8	Oh, and the cause... PO said he was riding along at 50 and heard a death rattle. Bike would crank and make a horrible noise. Then at some point the starter would click, and nothing moved. When i tore into it the piston was at TDC with a chunk of valve seat pinned between the piston and head, preventing full rotation. The guy at the head shop assumes unadjusted exhaust valves overheating, which i believe. There was a bit of an exhaust leak between the cylinder head and head, which makes me think the thing was running with wicked tight/overheating exhaust valves for a bit before detonation. Last edited by FreeRide; 02-07-2015 at 03:17 AM.
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01-26-2015, 02:25 PM	#5
Jordan_Ciaramitaro Junior Member Join Date: Jan 2015 Posts: 5	Ouch, have you checked to make sure the rod isn't bent? Is the piston damaged? I would clean that piston really good and look for hairline cracks. Login or Register to Remove Ads
	0

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01-16-2015, 12:34 AM	#2
Jordan_Ciaramitaro Junior Member Join Date: Jan 2015 Posts: 5	Unfortunately, the valve spring seat and valve seat are not the same. Any good machine shop should be able to source and install new valve seats for you. Looks like there is quite a bit of damage. Do you know what caused this? Maybe valves severely out of adjustment? Not sure if these are adjustable.
	0

02-04-2015, 10:41 PM	#6
FreeRide Junior Member Join Date: Jan 2015 Posts: 8	SOOOO CLOSE.. But stuck now.Help? I bought a new psiton, as the old one had been crunched by that chunk of valve seat enough that the rings were stuck. Crankshaft measures within spec though, luckily. So, im at the step of installing the piston on the crankshaft in the cylinder... I can get the new piston and rings into the cylinder on the bench jsut fine with a can-type ring compressor. Slides in easy, moves around nice, great. But, then i want to push the piston out the bottom of the cylinder enough to get the wrist pin installed to the crankarm, but this is far enough down to have the lowest ring pop off. The manual gives no advice how to do the assembly of the piston into the cylinder. Id install the piston onto the crank, then drop the cylinder down onto the piston using a ring compressor, but the taper at the bottom of the cylinder liner makes the band type compressors useless. Is this taper meant to guide the rings in as you tap the cylinder down from the top? Seems like a great way to trash some rings. What is the order of operations on installing a piston onto the crank, and getting it into the cylinder? Cant find any info anywhere. If only the damned ring was a sixteenth higher up the piston, you could insert the piston into the cylinder, then simple slide the wrist pin in, jsut like in this video.
	0

02-05-2015, 03:49 AM	#7
FreeRide Junior Member Join Date: Jan 2015 Posts: 8	Progress. Engine back together. Work flow for getting the piston installed, since i cant find it anywhere on the site. I took the starter out to do this, easy, 2 bolts. Rotated the crankshaft from the generator bolt until it was just below TDC with the crank on the rear side of the bike. Then put the starter back in. Now the starter is resisting the engine backdriving, so you can put a bit of downard force of the crank arm and it wont jut plunge down into the crankcase. Now, install the rings in the piston, as per manual, and attach piston to crank with wristpin and spring clips. New Gasket on, drop the cylinder jug over the cylinder studs until it rest on top of the piston, which should be well oiled, as well as the cylinder. Now, one by one, squeeze the rings as tight as possible by hand while jiggling the cylinder down onto the piston. This is positioning the crank arm jsut on the rear-tire side of TDC helps, lets you push down on the piston a bit. Didnt take much, as the tapered bottom of the cylinder sleeve does a good job of easing the rings in. Worked quite well. Then just rotated the crank a bit to make sure the piston moves smooth.
	0

02-06-2015, 06:10 PM	#8
Water Warrior 2 Senior Member Join Date: Dec 2006 Location: Squamish B.C Canada Posts: 11,409	A big+ for figuring out the puzzle.
	0

02-07-2015, 03:15 AM	#9
FreeRide Junior Member Join Date: Jan 2015 Posts: 8	It lives... Twitchy Neutral switch. Doesnt like to start with the kickstand down as it doesnt think its fimly in neutral. Gotta figure that out. Cleaned and checked the the little switch guy behind the engine countershaft sprocket, and its first harness connection under the seat. No issues, but its definitely a vibration effected problem. For now, ill keep the sidestand up, (the bike feels like a low-slung feather compared to my KLR anyway). Maybe ill just bypass the switch. Safety third, right? Also, those little individual motorcycle sized tappet feeler gauges are fantastic. And of course, after 5 weeks of no rain during what is supposed to be the rainy season here in CA, the afternoon i get her running.... rain. Wont complain wont complain wont complain
	0

02-07-2015, 03:24 AM	#10
FreeRide Junior Member Join Date: Jan 2015 Posts: 8	So... for the folks in the future who are considering what to do with a detonated top end... This may be premature, but the process seems to have worked. Total cost, not worrying too much about staying cheap, somewhere near 550-600. Had the cylinder honed, didnt really need it, but i wanted an excuse to learn from the guy at the shop. Brand spankin new head which came with a cam and rockers and cap i didnt need, new piston and rings. Also, bought all new gaskets, and had to buy some tools. Overall cost effective? Meh... dunno. But i got the bike for free with its exploded engine, and i got to take a top end down to the crankcase for the first time, which was really neat. So as an educational investment, very much worth it. And now ive got a cheap commuter bike so i can take my beat up KLR off line for some decades deferred maintenance. Ill let you guys know if there are any developments. Thank you for all your info.
	0