HELP PLease: GS650G valve clearance HUGE!!! 3.00 shim and has 14 thou clearance

[prichmon]

My son and I swapped a topend from 1 engine too another. When we pulled the buckets out of the head they all got rearranged. We slid them into the head and have 2 valves I can't get within spec. #3 and #1 exhaust vales are out; one measures 34 and other measured 25 thou over a 2.65 or so shim. All other valves I could bring within spec.

I tried swapping buckets from another head. No dice. The readings were off by a thou of two.

I have never seen this before. Only thing I can think of is we have a bent valve?

Anyone have any ideas?

Thanks

Rich

[Steve]

Yep, that much extra clearance sounds like bent valves or something is stuck on the seats, holding them open.

.

[Nessism]

Bent valve sound right.

Before installing a head in unknown condition it's advised to service it first. At minimum: remove valves, inspect all parts, lap the valves, and install new valve stem seals.

[Big T]

Any reason you can't go back to the original head?

[prichmon]

Orginal head

Any reason you can't go back to the original head?

I pulled the top end off the "black" engine due to a bad #2 rod knocking. The engine ran well with consistent compression across all 4 cylinders 155-165psi.

I pulled the silver topend due to bad rings on #2 cylinder and air leaking into the intake of #4 during a leak down test. When I pulled the head I filled the combustion chambers with water expecting #4 to poor out due to a bad valve or poor sealing. I had no loss out of any of the chambers. I don't trust the silver head since I have not found where the leak may be coming from..

My son is out of work due to covid so we are scraping pennies to get his bike running.

Thanks for the replies GSR team. I appreciate the guidance.

[bwringer]

See if you can manage some sort of leakdown test to see if that valve is leaking. As noted above, a bent valve or a little chunk of carbon on the seat are the usual suspects.

[prichmon]

Put air in the cylinders tonight and both blew hard out the exhaust. I ordered a valve spring compressor tonight. It looks like 1 and 3 exhaust are bent. I'll make sure once I disassemble.

[prichmon]

We opened it a couple days ago. I found both valves bent. The questionable head we are robbing parts from to fix the known decent one. As I was pulling seals since we had the head apart I had 2 snap off at the circlip line.

Now i'm replacing valve guides we are checking all the specs on the current parts.

Thanks GS team.

RR

[Nessism]

Realize that when replacing valve guides the valve seats will have to be cut too.

Sorry for the run of bad luck.

[prichmon]

No I didn't. Thanks for the heads up. POOP.

[prichmon]

Could you explain why?

[Nessism]

When the new guide is installed it will be every so slightly out of concentric with the old guide. And the guide is the datum for cutting the seats.

[prichmon]

So can they be lapped in or do I need to take it to a machine shop?

[Steve]

I would think that if they are non-concentric, no amount of lapping would get the valves to seat properly.

If the hole in the guide is off by 0.05mm, your lapping would just clean off a small portion of the seat.

And, ... if they DO have to address the seats, be sure to check valve clearance BEFORE putting the head on the engine. You might have to trim a bit off the tip of the valve if the seat is a bit deeper than before.

.

[prichmon]

OK. Thanks. Looks like we will make a trip to the machine shop.