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#60
by
Dakotakid
on 16 May, 2017 21:15
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According to Bentley:
Using NEW valve stems: 1.3 mm for exhaust..........1.0 mm for intakes
The exhaust stems are slightly smaller than the intakes.....even though they are both referred to as 8 mm stems. Obviously, the exhausts grow slightly larger with heat.
I use a 0.315 inch reamer for the exhaust followed with slight cleaning hone. I used a 0.3155 inch reamer for intakes followed with slight hone for smoothing. My job turns out slightly larger than the Bentley specs. I lose a little guide wear....but, I KNOW they will not stick in the new engine.
In the future, I will use the 0.315 in both holes and use more lubrication to get slightly tighter clearances.
There are also manufacturer differences in the stems (although (of course) not much). TRW's are slightly larger......Sealed Power and Osvats are a red-one smaller than the TRW's.
Of course, wobbling valves is not "accurate" as the guides wear oblong due to the rotational effect of the cam. But....what the hey............
I GUARANTEE you need at LEAST exhaust guides in virtually any used head.
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#61
by
Tmarkle
on 22 May, 2017 21:17
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Haven't gotten any farther with the car. I've become leery of taking the head to a machinist after reading horror stories of dropped precups. If I could afford a new head I would do that but that's not an option right now either.
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#62
by
Tmarkle
on 23 May, 2017 21:26
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Well I finally got the time and motivation to crack open the motor. Four valves appear to have hit pistons. On the bright side cylinders have virtually no lip (can't catch my nail) no prechamber cracks, and the head surface looked pretty good after some clean up. Is there a way to tell if the valves are bent or should it not even be investigated and just replace them?
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#63
by
Tmarkle
on 23 May, 2017 21:28
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#64
by
Tmarkle
on 23 May, 2017 21:29
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Also what's the best way to clean any debris out of the cylinders? Brake clean and air?
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#65
by
vanbcguy
on 23 May, 2017 22:37
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Valves tend to compress when hit - the stem gets fatigued but the valve stays "straight". The stem will be shortened slightly... There may be some noticeable wobble rolling the stem on a table but it often isn't all that obvious. This is the cause of a lot of trashed engines - people try to get away with just a new belt. The valve still seals so it "seems" like everything is good to go. Then a couple thousand miles later the head drops off the valve and completely DESTROYS the piston, head and possibly the block. If you're really lucky you bend a rod too.
New valves are cheap compared to the rest of the engine - once you have the valves pulled for inspection I'd be tempted to replace any that hit pistons.
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#66
by
libbydiesel
on 23 May, 2017 22:52
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New valves are cheap compared to the rest of the engine - once you have the valves pulled for inspection I'd be tempted to replace any that hit pistons.
Your post is right on except I think you're understating it a bit. If there is any indication
at all that a valve and a piston made contact I wouldn't just be tempted, I'd most certainly replace it.
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#67
by
Dakotakid
on 24 May, 2017 00:39
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If the valves are suspected units due to contact.....the lifters must be considered as well.
This is the first time I have ever seen true "first-over" pistons. I would go ahead and compare piston protrusion among the four. But, I would NOT pull those pistons unless you HAVE to because finding rings for those will be difficult......unless Hastings or some other off-beat. This is why you do not have much of a ridge.
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#68
by
RabbitJockey
on 24 May, 2017 04:47
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pull the lifters and flip them over, you can tell if there is damage
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#69
by
Tmarkle
on 24 May, 2017 05:25
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If the valves are suspected units due to contact.....the lifters must be considered as well.
This is the first time I have ever seen true "first-over" pistons. I would go ahead and compare piston protrusion among the four. But, I would NOT pull those pistons unless you HAVE to because finding rings for those will be difficult......unless Hastings or some other off-beat. This is why you do not have much of a ridge.
What would be a situation were I'd have to replace the pistons? I don't know if I mentioned that every single piston has a valve mark. Most of the marks are pretty much just visible but one has a ridge half way around I can catch my nail on easily (one pictured).
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#70
by
Tmarkle
on 24 May, 2017 05:27
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And what's a "first over" piston?
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#71
by
RabbitJockey
on 24 May, 2017 05:49
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pistons would depend on personal preference, they dont sound too bad, just make sure the rods aren't bent. I would only replaced them based on whether or not the engine needs overbored, which is decided by cylinder bore wear and compression numbers.
First over piston would be the first size over stock piston, so a 77mm piston because 0.50mm over size is the "first over" size piston.
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#72
by
Tmarkle
on 24 May, 2017 05:54
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pistons would depend on personal preference, they dont sound too bad, just make sure the rods aren't bent. I would only replaced them based on whether or not the engine needs overbored, which is decided by cylinder bore wear and compression numbers.
First over piston would be the first size over stock piston, so a 77mm piston because 0.50mm over size is the "first over" size piston.
Cylinders look good so I think that's ok. @dakotakid is saying that my engine has oversized pistons? Like it's been rebuilt once or was I misunderstanding his statement?
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#73
by
RabbitJockey
on 24 May, 2017 09:03
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looking and being are 2 different things haha
you can buy the two tools you need for measuring bores for less than 100 dollars if you're interested in being scientific about it
How ever in my opinion, if it had good cold starts before, didn't have a bunch of piston slap, didn't burn a bunch of oil, and the bores don't have any obvious problems then i wouldn't worry about it.
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#74
by
Dakotakid
on 24 May, 2017 11:20
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Markle: yes, that is exactly what I am saying. Look at the stamp on the top of the piston: "25/D" Indicates first over which is very infrequent and difficult to source those pistons and rings. However, this immediate middle section in the discussion makes me glad this forum still has the ignore feature. Headed there now................
