Performance Boats Forum banner

Sizing Guides for Marine Use

11K views 24 replies 12 participants last post by  thatguy 
#1 ·
Okay I'm no professional like several of you guys. I'm just a garage hack and build my own motors. I was not aware that the guides needed sized different for marine use, and I'm not suggesting that they don't need special clearances. However, given the number of engines I have built over the years, without any guide failures, leaves me wondering why they need special sizing, or why I haven't had any guide issues? My latest build (http://www.performanceboats.com/dyno/58837-dyno-results.html) used AFR heads but my head guy supplied the valves and springs. Since the new motor currently has less than an hour of run time, off the dyno, do I need to pull the heads to check the guides?
 
#2 ·
[HR][/HR]AFR specifically says in their tech sheet (included with the heads) that their guides are on the tight side and for blown/Nos or marine use, they advise more guide clearance.
Last year I had to do a complete rebuild on a set of AFR 325 heads for a customer who had someone else build the heads, supplied the ex valves, and didn't check the guide clearances. There were clear signs of the ex valves running hot and dragging in the guides. Fortunately (his was a centrifugal blown engine) he hadn't really stuck his foot in it yet, because from what I was seeing on the ex valve stems, he was one hot-foot run from sticking an ex valve. I tell you this in detail to let you know your engine can be running, but you could still be risking sticking a valve which we all know can be catastrophic. Also note: the valves AFR uses are a few tenths smaller than, say, a REV or a Ferrea, so when you stick an aftermarket valve in the head, like this last case scenario I explained, you end up with even less clearance than what AFR is already telling you is minimum.
As far as other heads, most have generous enough clearance that it's not an issue, but for me, it's always a good idea to check.
HTH
 
#3 ·
pistons need more clearance in marine motors because the block never gets hot enough to expand to size, valve stems only care about guide material & fuel, ex valves that don't have enough clearance stick pretty quick, intake valves need to be on the tight side to keep oil out of the combustion chamber. valve stem seals are suppose to be a controlled oil leak. ski boat motors valve guide seals should be a pc on the intake & umbrella seal on the ex.
 
#6 ·
What valve stem to guide clearance is considered to be "marine spec" for your typical lake ski BBC motor. More Specific, Aluminum heads with bronze guides and Inconel valves? (Darts/Brodix):idea: Does the spec change when we start talking about "GM iron" 990's, 781's?

I'm just a DIY garage hack that builds his own motors for fun and education too. This forum gets read by me every morning over coffee and is chalked full of great info.:)coffee There are a lot of astute individuals that post here and much can be learned if one pays attention.:)hammers Thanks for all the replies and good posts!:D
 
#7 ·
Ashumtoy, couple of reasons you may not have had any problems is, one your lucky. But as much as anything, it could be the way you drive the boat. Not to say you don't hammer the sumbitch. But you do it after its good and warm.

When water cooled 2 stroke bikes first came out, they had a bad problem with sticking the piston big time. What was happening was that the rider would "warm" up the bike, and them hammer it. Well the water wasn't warm, and really, neither was the cylinder. But when it got hammered, the piston would go to temp in a heart beat and the thing would stick. An exhaust valve and guide isn't a whole lot different.
The whole engine has a much better chance of surviving less than ideal clearances if the thing is fully warmed up before the fuel is layed to it.

Your heads may have simply been looser without you knowing it. Steelcomp had an issue with loose guides from Patriot heads, even after returning them.
Also, long overlap cams and high compression helps alittle. Low compression and short overlaps tend to create more exhaust heat combined with less intake cooling during the overlap event. Also, even though the guide doesn't expand as much in a lake cooled engine, a huge part of the exhaust valve's heat is rejected thru the seat and the stem. Both are much cooler in a marine engine. Even though a marine engine generates alot more combustion heat due to load, the exhaust valve is able to reject much more heat due to the cooler seat and guide.

Bottom line, all marine engine should have the guides set accordingly, but blower and NOS marine engines seem to be much more problematic than N/A deals. JMO.

I try not to worry too much about this crap and just let Steel handle it. That way if I stick a valve, I know whos ass needs whooping.:wink2:



 
#13 ·
I bought a set of assembled heads from afr (bbc 325's) and told them i was running marine with a blower. After reading a few threads on here I took them to Tim at Morgans Machine since he is right down the street from me. He said the guides were way too tight and probably wouldn't have lasted long on my application. So again thanks to the guys here on performance boats for the the helpfull advice. So i would also recommend having the heads checked out by a professional.
 
#14 ·
I may take some smack for this, but if you want to buy a set of ready to bolt on AFRs, the best place to get them is thru Teague. He gets them bare, does all prep, and final machining, uses manely Severe intakes, Extreme exhausts, and Isky springs and retainers, and they are only slightly more than getting them from Summit, Jegs or AFR.

HOWEVER...if Steel is up and running yet, getting AFRs thru Cstraub is another excellent place as well. Well Scott, are you doing heads yet???? Are you sitting up Canfields yet?
 
#18 ·
On a related note, I'd like to hear the pros opinion on valve stem seals and guide material.

I quit running positive seals years ago. When I was still doing heads for customers.
I had seat and guide machine and full Winona bronze guide tooling, in conjunction with a Sunnen guide hone to finish size. Those heli-coil type guides needed oil, it seemed, or they would destroy a valve stem.
It seemed that on anything that didn't get tore down every week, I would see stem wear from the seal/ top of guide area.
I just do my junk now, but on my Brodix with SS valve stems I run only an umbrella seal on the intakes and no ex. seal at all.

They were at .002 +- .0002 this winter, after 2 summers (maybe 40 hours actual run time? All hard running). Started at .0018 last head service. (I checked them when changing springs earlier this year.)

when I pull the heads this winter, what type of replacement guide/ insert would the pros run in these Brodix heads? They are Brodix bronze originals now.
I have guide drivers still, and can change solid guides but will have to farm out the finish hone.

Lake jet, 454, Hyd roller, 4000 - 5400 RPM at all times except idling in no wake zones.
 
#24 · (Edited)
The best guides you can buy are from CHE. There are decent guides from PEP and other manufacturers. The biggest difference between them being the concentricity of the ID and OD of the guide and the CHE guides are more accurate and a better material than the others IMO. Assuming you're checking valve stem wear as well o guide clearance. Of course, after replacing guides you're going to need a valve job.
Stem seals...kind of a personal thing. I run them on int and ex, but I know lots of guys don't. Valve stems need to be hard chrome and polished when running bronze guides. The old Winona guide liners were really hard on valves. Anywhere that I have to use liners, I use K Liners.
I would not run inserts in a bronze guide, just replace the guide. DO NOT DRIVE THE GUIDE OUT FROM THE VALVE SIDE! Cut the top of the guide off flush with the head and drive out from the spring side. This is the only way to insure not damaging the guide bore. Otherwise you'll have to re-ream the guide bore and install an oversized guide. You also need to be able to measure the guide bore so you can get a guide with the right amount of press. Bronze guide in aluminum, no less than .0015, no more than .002.

You can get CHE guides direct from CHE. Google is your friend. You can also get replacement guides from Brodix and you can get guides form CV products as well. CHE will want to know all the dimensions of the guides, so be prepared for that.
 
#19 ·
I likes 2 run mine on the loose side of loose. I cans tell just how loose by the tone of the clunk :p:p



And yes, it ran that way....with no obvious problems. Even had decent compression. Best guess it was caused by a poor finish on the valve stems local machine shop missed it twice. All 8 intakes were like that.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top