Top end question
07-25-2005, 12:28 PM
#1
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Top end question
Hate to admit it, but I screwed up my top end last summer when on a trip the CCT went kaput. I replaced the valves and guide seals, but not the guides (Why, you ask? I guess cause I'm just dumb 
.
Anyway, looks like I'm getting some oil leakage there and I'm looking at another rebuild. Questions for you experienced gear heads out there: Should I rebuild what I've got (replacement part running around $400) or buy some used heads and simply bolt them on (costing around $150)?
If I go the rebuild route, can I just replace the guides or should the valves also be replaced (keep in mind the valves have about 8K on them). Same question for the guide seals - should they be replaced too, even though they are relatively new?
Thanks for the input.
.Anyway, looks like I'm getting some oil leakage there and I'm looking at another rebuild. Questions for you experienced gear heads out there: Should I rebuild what I've got (replacement part running around $400) or buy some used heads and simply bolt them on (costing around $150)?
If I go the rebuild route, can I just replace the guides or should the valves also be replaced (keep in mind the valves have about 8K on them). Same question for the guide seals - should they be replaced too, even though they are relatively new?
Thanks for the input.
07-25-2005, 02:30 PM
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You always replace the seals. You measure the guide bores to determine whether to replace them. Valves are replaced when they are burnt, cracked or can't be refaced.
Do you mean there is oil draining into the cylinders?
Do you mean there is oil draining into the cylinders?
07-25-2005, 03:33 PM
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This past weekend I was on a group ride and the rider behind me mentioned he saw smoke when I was downshifting, an indication that oil was getting in via the guides (as opposed to the rings).
I don't know about his assessment, but it makes sense to me since I did top end work last year. (I figure I should have replaced the guides. No, I didn't measure them, both because I didn't think of it and because I was in a bit of a predicament.)
On the other hand, the motor has about 41k on it - any possiblitiy that the cylinders are out-of-round? My next step was going to be checking the compression.
Thanks
07-25-2005, 04:25 PM
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That oil usage would be considered normal by Honda.
I don't know of much experience with higher mileage VTRs, but it could be any of the ideas you've had.
A compression check will answer your question about rings, but not if just the oil-control side rail is bad. The idea that oil on downshifting indicates guide seals is not correct.
Top end oil drip shows as blue smoke on startup (since the oil has had all night to leak down.) Blue smoke while running could be either but is more probably rings.
BTW, to measure the guides, you'll use ball gauges and a micrometer. Neither is too expensive. To measure cylinder round you'll need the proper bore guage. Its usually a more expensive tool. Wall damage will be obvious.
I don't know of much experience with higher mileage VTRs, but it could be any of the ideas you've had.
A compression check will answer your question about rings, but not if just the oil-control side rail is bad. The idea that oil on downshifting indicates guide seals is not correct.
Top end oil drip shows as blue smoke on startup (since the oil has had all night to leak down.) Blue smoke while running could be either but is more probably rings.
BTW, to measure the guides, you'll use ball gauges and a micrometer. Neither is too expensive. To measure cylinder round you'll need the proper bore guage. Its usually a more expensive tool. Wall damage will be obvious.
07-25-2005, 04:43 PM
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Re: Top end question
Thanks
Yeah, unfortunately it's not due to overfilling.
I'm surprised Honda would consider losing a qrt at that rate to be "normal."
I'm not sure about the downshifting symptom. Maybe it's more of a deceleration thing? I'm wondering if it could be smoking then because the throttle is closed but the pistons are creating a vacumm which ends up drawing oil down through the guides??
I'd really rather not have tear the engine down to do a cylinder job - please say it ain't that.
Your analysis about smoke at start-up is right, though.
Yeah, unfortunately it's not due to overfilling.
I'm surprised Honda would consider losing a qrt at that rate to be "normal."
I'm not sure about the downshifting symptom. Maybe it's more of a deceleration thing? I'm wondering if it could be smoking then because the throttle is closed but the pistons are creating a vacumm which ends up drawing oil down through the guides??
I'd really rather not have tear the engine down to do a cylinder job - please say it ain't that.
Your analysis about smoke at start-up is right, though.
07-25-2005, 05:15 PM
#8
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Re: Top end question
High oil consumption in the big Honda twins is common, due in part to low ring pressure (the rings are thin, light and not very stiff). The other characteristic of these engines that contributes is that the cylinders are unsupported at the top, where the heat is highest and they tend to go out of round. the good news is, they run fine in this condition. Apparently, even the race engines tolerate a higher than usual out of round condition, because of the big bore.
Black deposit on the back sides of the valves is due more to crappy fuel and not necessarily oil coming down the guides.
Valve guides do not necessarily need replacement. their main function is to guide the valve in to the seat. Worn valve guides tend to wear the valve seats more quickly. the valve stem seals meter the amount of oil getting to the valve stems.
If the valve guides are replaced, you must recut the valve seats as they will no longer be concentric with the guides. The main shortcut you took in replacing the vavles is not recutting the seats. High RPM engines require high valve seat pressures because stiff springs are required to prevent the valves from floating off the cams (one of the main factors in determining engine redline). The exhaust seats will show signs of pitting after 12k miles or so. Pitting continues at an increasing rate at higher mileage due to less heat transfer. I recut my valve seats after 2 seasons.
40k miles is a lot. I agree with jschmidt, it sounds like rings to me. You may get away with honing and new rings. You'll have to measure the cylinders to know for sure. If it was me, I'd run it for the season and make it fresh over the winter.
If you buy another engine, you'll pay a lot for an unknown quantity, then pay to have it shipped.
Good Luck.
RC
Black deposit on the back sides of the valves is due more to crappy fuel and not necessarily oil coming down the guides.
Valve guides do not necessarily need replacement. their main function is to guide the valve in to the seat. Worn valve guides tend to wear the valve seats more quickly. the valve stem seals meter the amount of oil getting to the valve stems.
If the valve guides are replaced, you must recut the valve seats as they will no longer be concentric with the guides. The main shortcut you took in replacing the vavles is not recutting the seats. High RPM engines require high valve seat pressures because stiff springs are required to prevent the valves from floating off the cams (one of the main factors in determining engine redline). The exhaust seats will show signs of pitting after 12k miles or so. Pitting continues at an increasing rate at higher mileage due to less heat transfer. I recut my valve seats after 2 seasons.
40k miles is a lot. I agree with jschmidt, it sounds like rings to me. You may get away with honing and new rings. You'll have to measure the cylinders to know for sure. If it was me, I'd run it for the season and make it fresh over the winter.
If you buy another engine, you'll pay a lot for an unknown quantity, then pay to have it shipped.
Good Luck.
RC
07-25-2005, 05:34 PM
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Thanks for the thorough reply rc996.
Although I didn't re-cut the valve seats, I did lap the seats using lapping compound and gingerly spinning the valve with a drill.
Yeah, the valves and seats were pitted (that was at about 32K). I figured it was due to a dirty air filter making for a rich mix.
Although I didn't re-cut the valve seats, I did lap the seats using lapping compound and gingerly spinning the valve with a drill.
Yeah, the valves and seats were pitted (that was at about 32K). I figured it was due to a dirty air filter making for a rich mix.
07-28-2005, 10:34 AM
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Re: Top end question
gadjet ,
I bought a new 2003 SuperHawk in late 2004 . I put 580 easy miles on it then pulled it out and put a race motor in the bike .
It's complete from starter to airbox and guaranteed perfect .
You cannot rebuild your engine for the $950.00 I'll take for this one . If interested , give me a PM .
I bought a new 2003 SuperHawk in late 2004 . I put 580 easy miles on it then pulled it out and put a race motor in the bike .
It's complete from starter to airbox and guaranteed perfect .
You cannot rebuild your engine for the $950.00 I'll take for this one . If interested , give me a PM .
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