Just discovered that the engine I need to rebuild has been rebuilt before - Honda Motorcycles - FireBlades.org
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post #1 of 27 Old 09-07-2009, 3:39 AM Thread Starter
 
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Just discovered that the engine I need to rebuild has been rebuilt before

Started to spec out the cylinders for the rebuild and discovered they were waaay over the 71.000 to 71.015 for a stock 900RR. I checked and rechecked and sure enough the cylinders had already been overbored to 72mm, well a shade less actually. Took one of the pistons and cleaned the carbon off with a dremel and wire wheel for polishing and the numbers match the same part numbers used at Wiseco for they're overbore kit.

Well guess I don't have to spend that $755.00 on the piston kit now. Now I know why the valve didn't hurt the piston when it struck it and broke, the pistons are forged. So does anyone have any idea what 945cc with a 12:1 CR (vs 919 with 11:1(?) CR) was putting out HP wise?

Also, can anyone approximate how much material honing removes from the cylinder? I'm hoping not very much or I'll be forced to resleeve and overbore to 73mm.

Last edited by unfetteredmight; 09-07-2009 at 3:56 AM.
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post #2 of 27 Old 09-07-2009, 4:58 AM
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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Started to spec out the cylinders for the rebuild and discovered they were waaay over the 71.000 to 71.015 for a stock 900RR. I checked and rechecked and sure enough the cylinders had already been overbored to 72mm, well a shade less actually. Took one of the pistons and cleaned the carbon off with a dremel and wire wheel for polishing and the numbers match the same part numbers used at Wiseco for they're overbore kit.

Well guess I don't have to spend that $755.00 on the piston kit now. Now I know why the valve didn't hurt the piston when it struck it and broke, the pistons are forged. So does anyone have any idea what 945cc with a 12:1 CR (vs 919 with 11:1(?) CR) was putting out HP wise?

Also, can anyone approximate how much material honing removes from the cylinder? I'm hoping not very much or I'll be forced to resleeve and overbore to 73mm.
Nice find :-)
I'm building a car engine that's been bored +1mm as well but pistons are just stock over-size junk :-(
You can probably work on roughly equal percentages so probably 2-3% over stock. The compression is probably worth 1-2% so you might be up 5% over stock if everything else is good.
If it's already been opened up I'd suggest measuring the cams to see if they're stock as well.
You will have to measure the pistons and ring grooves to know if they're still usable but I'd expect them to be okay. Piston-to-bore clearances will tell you if you need to bore it. I wouldn't have thought you'd have to resleeve to go +2mm in iron bores though.
Honing is normally only a few thou. Normally you would give your block and pistons to the guy doing the boring and he'll bore just under and then hone to the required finished size.

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post #3 of 27 Old 09-07-2009, 12:08 PM Thread Starter
 
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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Nice find :-)
I'm building a car engine that's been bored +1mm as well but pistons are just stock over-size junk :-(
You can probably work on roughly equal percentages so probably 2-3% over stock. The compression is probably worth 1-2% so you might be up 5% over stock if everything else is good.
If it's already been opened up I'd suggest measuring the cams to see if they're stock as well.
You will have to measure the pistons and ring grooves to know if they're still usable but I'd expect them to be okay. Piston-to-bore clearances will tell you if you need to bore it. I wouldn't have thought you'd have to resleeve to go +2mm in iron bores though.
Honing is normally only a few thou. Normally you would give your block and pistons to the guy doing the boring and he'll bore just under and then hone to the required finished size.
Yeah I was kinda excited when I found out they were forged pistons, bummer on the car man. Just checked the intake cam and the lobe height was 36.0680mm, so stock cams according to the specs in my shop manual. Maybe I should fix that "problem"

Any suggestions on a cam I should step up to?

Wouldn't my volumetric efficiency have dropped because of the increase in bore size without increasing air flow?

What would you do?

I haven't checked the pistons yet, hopefully your right and they'll be fine. I just went through all the bores at three points (top,middle,bottom) on two axis, and the largest was 71.9886, so I'm golden there on a hone. The only thing I'm going by on saying I would have had to resleeve was the info on Wiseco's site, so I assume it's accurate. I'm just glad I don't have to.
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post #4 of 27 Old 09-07-2009, 12:18 PM Thread Starter
 
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

Any idea what the stock valve sizes are on a 919? I can't seem to find the spec in my shop manual.
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post #5 of 27 Old 09-07-2009, 12:31 PM
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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Yeah I was kinda excited when I found out they were forged pistons, bummer on the car man. Just checked the intake cam and the lobe height was 36.0680mm, so stock cams according to the specs in my shop manual. Maybe I should fix that "problem"

Any suggestions on a cam I should step up to?

Wouldn't my volumetric efficiency have dropped because of the increase in bore size without increasing air flow?

What would you do?

I haven't checked the pistons yet, hopefully your right and they'll be fine. I just went through all the bores at three points (top,middle,bottom) on two axis, and the largest was 71.9886, so I'm golden there on a hone. The only thing I'm going by on saying I would have had to resleeve was the info on Wiseco's site, so I assume it's accurate. I'm just glad I don't have to.
I can't suggest a cam as it depends on what other modifications you have and what results you want. I'd probably suggest something that's not so wild you'd need new springs or lifters though.
I'm very surprised but you're right, 2mm requires resleeving according to Wiseco. Even the aluminium 929 bores can go +2mm. Can you measure the wall thickness of the liners?
VE is complicated. Keeping the ports smaller can boost midrange. Hogging them out tends to push the power up the tach. Can you get a stock head for comparison to see if yours has been ported? Maybe photos of the intake and exhaust ports and bowls? It might be worth comfirming the valves are stock sizes as well.
Because the engine I'm doing has been bored already, I'm measuring everything as you never know what may have been done before. I know mine has blown up at least once as the pickup was still full of bits of bearing shells. I'm bolting the crank in dry to plasti-gauge the clearances and then I'll do the same with the rods and bolt the head down to measure piston-to-valve clearances.
I'd recommend doing the same with yours.
If it's been bored because it blew up at some point then it may also have had the head milled if it was warped. Unless you can find the stock head thickness measurement the best way to be sure is to measure it yourself. Also measure your crank journals accurately before ordering shells as a journal may have been machined down from what's stamped on the crank.

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post #6 of 27 Old 09-07-2009, 12:39 PM
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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Any idea what the stock valve sizes are on a 919? I can't seem to find the spec in my shop manual.
I've got a _very_ vague idea they're 23mm and 27.5mm but I'd have to confirm.

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post #7 of 27 Old 09-07-2009, 12:46 PM
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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I've got a _very_ vague idea they're 23mm and 27.5mm but I'd have to confirm.
Just checked Ferrea and it looks like 23mm and 27.5mm are stock.
Ferrea Racing Components

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post #8 of 27 Old 09-07-2009, 12:49 PM Thread Starter
 
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

These were taken kinda fast, i have my little ones. That's why I posted that first message so early in the morning, it's the only time I can work on it without distraction, lol.

Liner thickness to water jacket is 6.4770mm
Liner thickness in between liners is 7.2390mm
They were the smallest amounts found.
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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Just checked Ferrea and it looks like 23mm and 27.5mm are stock.
Ferrea Racing Components
Good memory. Cool, thanks. Now once I disassemble the head I can measure the valve sizes and see if they are stock. I tried with the valves still in the head......not gonna happen.
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

Larry.. i see you got your membership renewed

IM OLD GREEEEEEG!!!
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post #11 of 27 Old 09-07-2009, 12:56 PM Thread Starter
 
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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Larry.. i see you got your membership renewed
I actually like this site enough to become a supporting member myself in a couple days. That's really saying something because of all the forums I've ever been a part of in my 34 years, it would be the first time I paid for a membership.
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post #12 of 27 Old 09-07-2009, 12:59 PM
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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These were taken kinda fast, i have my little ones. That's why I posted that first message so early in the morning, it's the only time I can work on it without distraction, lol.

Liner thickness to water jacket is 6.4770mm
Liner thickness in between liners is 7.2390mm
They were the smallest amounts found.
6.5mm is huge so I'm guessing that's the liner and the aluminium jacket around it? You should be able to see the bottom of the liner to measure just the sleeve.
7.25mm with 72mm bores is 79.25mm bore spacing which seems on the tight side. The 929/954 are 81mm.

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post #13 of 27 Old 09-07-2009, 1:01 PM
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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Larry.. i see you got your membership renewed
Took me a while to work out what was happening :-)
It kept telling me I had 600 messages over my storage limit so I had to cull those to get PM working again. Then I realised I couldn't see who repped me and that my picture was missing.
Eventually I worked it out :-)

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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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Good memory.
Actually, I have a _hopeless_ memory :-)
Really there aren't that many options for 900cc four-valve heads so they were likely to be 23-25mm and 27-30mm and I remembered the 900RR has very small valves - even smaller than the GSXR750.

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post #15 of 27 Old 09-07-2009, 1:19 PM
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Re: Just discovered that the engine I need to rebuild has been rebuilt before

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I actually like this site enough to become a supporting member myself in a couple days. That's really saying something because of all the forums I've ever been a part of in my 34 years, it would be the first time I paid for a membership.
I've been on lots of forums over the years and I regularly sign up to new ones when I'm chasing obscure infomation like rod lengths or bore spacing.
Like Fireblades, XS650Garage and TeamSwift are great forums with lots of good information and lots of good helpful members but generally I haven't been impressed with most people that like to hang out online.
There is a very large local riders forum here but it's so full of dickheads I very rarely log-in. Really the only times I do are when some idiot rider makes the news for doing dumb stuff or a rider gets killed doing dumb stuff as it's a given they'll be members there.
Spending five minutes at Stuntlife is enough to remind me why I stay with a select few forums :-)
I think the first forum I joined would have been Peter Parker's GSXR Mailing List in the late nineties.

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