Logo
FULL SITE MENU

1964 Speeditwin / rebuild too tight?

K

Kdiddle

New member
Hi all. Quick background - dug out my grandad's old Speeditwin 28hp and went through it pretty thoroughly. Replaced bearings / resealed lower unit, bored out block, new pistons/rings (.40 over), new fuel pump/lines, replaced all electrical components, rebuilt the carb and put everything back together with new gaskets.

I understand there is a pretty specific break in procedure and am currently running 24:1 (non-ethanol) mix through my engine. I have so far ran roughly 6gal through my engine, initially running it at fast idle, keeping the speed varied and eventually taking it out on the water to get the engine speed a little higher.

Problem is it doesn't seem to run 'well', regardless of where I set my high speed setting. Towards the end of my tank I was finally able to get it on plane for a few brief seconds, but a couple of times the engine would slow down and basically seize up when it was under power. Which leads me to my question - it is possible my pistons/rings are too tight and it just needs to be broken in more? I verified the ring gap was within tolerance before installing the pistons, but it feels like they're getting hot under load and making the engine stop. Once the engine cools for a sec, its able to run again, but I stopped running it for fear of doing further damage.
 
You did install a new pump impeller ?------You did line up the bearings and dowel pins when you installed the crankshaft ??-----After the finish honing what was the clearance between the piston and bore ?-=--Piston is measured at bottom of the skirt.
 
racerone said:
You did install a new pump impeller ?------You did line up the bearings and dowel pins when you installed the crankshaft ??-----After the finish honing what was the clearance between the piston and bore ?-=--Piston is measured at bottom of the skirt.
Click to expand...

Thanks for the reply, racerone.

Yep, new impeller and its spitting warm water when its running. Bearings/pins were lined up carefully (it was a total pain in the neck). I don't remember the exact #, but the piston gap was well within the gap provided in the service manual. I had it checked by the machine shop that performed the bore and even sent him my new pistons when I had it bored.
 
You adjusted the airgap on the coils ?----Are coils possibly rubbing on the flywheel ?-----You lined up the connecting rod caps ?----If engine locks up solid then you need to find out why before running it again !!
 
Coils were adjusted and when its not running, there is no drag on the engine at all. The flywheel spins freely (up to compression stroke obviously). Yep, connecting rods were carefully aligned and put back like they came off (since the service manual said that was important). The pistons (and rings) I installed were original OMC brand purchased from this site.

Let me ask it this way - how long should it be before my engine runs at anything close to full power? Should it take some time to get engine fully broken in before it should pull at full power? I understand I have to adjust the high speed needle first, but it seems that no matter where I put the needle that it is still not pulling what I think it should (lending credence to maybe things still being too tight).

I don't mind keeping the mix super rich and continuing to run it a lower speed to get things broken in as it only seemed to 'seize up' when it was running at full throttle when it was producing a fair amount of power...
 
When you say "basically seize up"....... Are you saying that, in actuality, the power-head is locked up solid, that the flywheel cannot be turned by hand..... and that you must let it sit 1/2 hour or so for it to cool off in order for it to turn over again?
 
Last edited:
It was a very low speed 'seize' but it was much faster than just turning the engine off and letting it spin down (like it was out of gas). However, it wasn't a hard lock up. More of a fast deceleration accompanied by some knocking noise. I only let it happened a couple of times. The first time it cranked immediately after the seize, the second time it was so tight the starter wouldn't spin it but after 15 mins or so it was able to spin again with the starter. I only spun it to see if it was still locked and put it back on the trailer as I was worried I was going to ruin all my hard work.

It never had any issue when running at a fast idle/mid throttle, it was just kind anemic, which is why I wanted to get it opened up so I could get it broken in correctly.
 
BTW - thank you all for your feedback/questions. Its a tremendous help to hear from folks that are used to working on these old timers. Its just discouraging as I don't want to find out that I'm blown up all my hard work....

One question about the high speed needle - the service manual is vague about tuning during break in, only that you should adjust high speed to 'best power'. Is that safe to do now? Or do I have to wait a while to lean it out for best power?
 
Could this be a lean seizure? I've had this issue with jet skis, the cylinder doesn't get enough fuel causing the piston to overheat and swell in the bore.

KJ
 
You should be able to get full throttle 2 minutes or less after you first start it !!-----Now that may not be a good procedure but it does not take 10 hrs before the motor can go to full throttle !!-----Find out what is wrong here.----Mabe take bypass covers off for a look see.-----And check for piston clearance with those covers off.
 
Last edited:
racerone said:
You should be able to get full throttle 2 minutes or less after you first start it !!-----Now that may not be a good procedure but it does not take 10 hrs before the motor can go to full throttle !!-----Find out what is wrong here.----Mabe take bypass covers off for a look see.-----And check for piston clearance with those covers off.
Click to expand...

Agreed, it should not seize. In fact, I think the manual probably says to run full throttle to get it up on plane, then back off a bit. It is almost impossible to sit here and tell what you did wrong. Wild guess: You say you have the manual, so did you install the wrist pins from the correct side, as the book says?
 
The exhaust relief outlet hole... about halfway down the rear portion of the long exhaust housing... water should be shooting out that hole like water blasting out of a garden hose at full blast at "all" rpms. Does it?

Wondering if that engine has been overheating (water pump) instead of a mechanical problem (bore/rings/whatever).
 
No, the water coming out of the exhaust port is merely a fast trickle, but it doesn't seem particularly hot. I've been able to touch the outside of the engine but it doesn't seem like its overly hot. I installed a new impeller and made sure it was oriented correctly and on the keyway before installation. Any idea how it could be working partially and not putting out full water pressure?

Now that you mention it, when the engine was running and warm it was producing white smoke that appeared to be steam and not oil smoke...

Dang. I hope I haven't fubared my engine...
 
BTW - I spoke with the machine shop yesterday. He confirmed that my piston/bore clearance was .0040 and the service manual says .003-.0045 is acceptable, so it sounds like that shouldn't be the issue.
 
You might try running a 50 to 1 mixture at idle to see if the 24 to 1 may have anything to do with the "low speed seize". I agree that at full speed, the water coming out the back of the motor should be a lot more than a trickle. As I remember, it should be more like about 1/2 of what comes out of garden hose when the spigot is fully open.
 
Its definitely less than even half a garden hose worth, but its definitely moving some water. Guess I'll take the foot off and see if the grommet isn't seated well in the water pump housing or something. I can't think of what else could be causing it to have reduced water flow. I checked all the water jacket galleys while I had it apart and they were perfectly clean, unless there's a partially blocked passage somewhere...
 
64 was the first year for 50:1 mix.------Break in would be done with double the oil at 24:1 mix.------Time to do the simple stuff !!-----Remove bypass covers to inspect for damage !
 
Racerone - looks like that'll be my next step. Do you know if its possible to pull the bypass covers without removing the powerhead? I seem to recall some of those screws might sit down in the engine housing pretty low.
 
??----Just look at your motor !----The 2 intake bypass covers are easy to remove without removing the powerhead.-----Ignore the exhaust cover for now !
 
Kdiddle said:
No, the water coming out of the exhaust port is merely a fast trickle, but it doesn't seem particularly hot. I've been able to touch the outside of the engine but it doesn't seem like its overly hot. I installed a new impeller and made sure it was oriented correctly and on the keyway before installation. Any idea how it could be working partially and not putting out full water pressure? Now that you mention it, when the engine was running and warm it was producing white smoke that appeared to be steam and not oil smoke...
Click to expand...

Too bad you failed to mention that in your first post. Perhaps you hit the edge of the water pump grommet and folded it over with the copper water tube, something of that nature. At any rate, you have a water supply problem it appears. Drop the lower unit and inspect your work.

On that model, the impeller can be installed either side up... and it doesn't matter which way it's turned to install as the rotation of the engine will correct the direction of the vanes immediately upon cranking over.

The "white smoke" indicates water being boiled... keeping it simple. This is usually caused by a failed head gasket or some other problem in the head gasket sealing area. Do a compression check and let us know what the psi readings are on the individual cylinders.

If the head gasket or sealing area is flawed for any reason, a "stalemate" occurs! Water is trying to come up from the pump, combustion from the cylinder is going down, the two meet... stalemate... the water just sits there and boils!

If indeed that engine has seized due to overheating, the power-head bolts "all", especially the head bolts will need to be tightened/torqued. The head bolt torque is 18 to 20 foot pounds in the following sequence whereas each number is a bolt.

9...10
5....6
1....2
4....3
8....7
 
Welp, I haven't even begun to troubleshoot the cooling issue but it may not matter anyway. Take a gander at that brand new piston/rings from the intake port. :-(

It it even worth checking the compression at this point? Or could I potentially damage my cylinder walls doing that?
 
You made mistakes !!!-----The motor is junk and needs to come apart to see what went wrong.-----No point in doing a compression test on that at all !----Your location ?
 
Yeah, that's where I was headed. I'm in GA, near Atlanta. Know of any good antique engine mechanics? The few I called wouldn't even look at it...

Teardown 2.0, here I come...
 
Well, I am a 1000 miles away so can not help.-----There must be folks from the ----aomci ----in your area.----Often they can help with parts and a tutorial for you
 
What diameter did they bore and finish hone to ?----Where on the piston did they measure the diameter ?----What clearance was there between piston and bore.----Answers will help YOU determine what may have gone wrong !!
 
Back
Top